SERV1830_TXT

SERV1830January 2007

TECHNICAL PRESENTATION

773F (EED), 775F (DLS)OFF-HIGHWAY TRUCKS

INTRODUCTION

Service Training Meeting Guide(STMG)

GLOBAL SERVICE LEARNING

773F (EED), 775F (DLS) OFF-HIGHWAYTRUCKS - INTRODUCTION

MEETING GUIDE 830 VISUALS AND SCRIPT

AUDIENCE

Level II - Service personnel who understand the principles of machine system operation,diagnostic equipment, and procedures for testing and adjusting.

CONTENT

This presentation provides basic maintenance information and describes the systems operationof the monitoring system, engine, power train, steering, hoist and brakes for the 773F/775F Off-highway Trucks. The Automatic Retarder Control (ARC) and the Traction Control System(TCS) are also discussed.

OBJECTIVES

After learning the information in this meeting guide, the serviceman will be able to:1. locate and identify the major components in the engine, power train, steering, and

brakes;

2. explain the operation of the major components in the systems; and

3. trace the flow of oil through the systems.

REFERENCES

773F/775F Operation and Maintenance Manual SEBU7794773F/775F Parts Manual SEBP4306

PREREQUISITES

"Fundamentals of Engines Self Study Course" TEMV3001"Fundamentals of Mobile Hydraulics Self Study Course" TEMV3002"Fundamentals of Power Trains Self Study Course" TEMV3003"Fundamentals of Electrical Systems Self Study Course" TEMV3004STMG546 "Graphic Fluid Power Symbols" SESV1546

Estimated Time: 24 HoursVisuals: 213Handouts: 24Form: SERV1830Date: 1/07

© 2007 Caterpillar Inc.

SUPPLEMENTAL MATERIAL

Reference Manuals

Fluid Power Graphic Symbols User's Guide SENR3981Cold Weather Recommendations for Caterpillar Machines SEBU5898Caterpillar Machine Fluids Recommendations SEBU6250

Salesgrams and Product Bulletins

Training Bulletin "Caterpillar Transmission/Drive Train Oil" TEJB1002Product Bulletin "Reporting Particle Count By ISO Code" PEJT5025Salesgram "Caterpillar Extended Life Coolant" TEKQ0072Product Data Sheet "Caterpillar Extended Life Coolant" PEHP4036

Technical Instruction Modules on Legacy DVDs SERV1000-01(These materials CANNOT be ordered separately.)

Automatic Retarder Control System SEGV2593Automatic Electronic Traction Aid SEGV2585769C - 793B Off-highway Trucks--Suspension System SEGV2599Truck Payload Measurement System SEGV2579

Service Training Meeting Guides

STMG 713 "769D/771D/773D/775D Off-highway Trucks" SERV1713

Video Tapes

Suspension Cylinder Charging TEVN2155TPMS Management/Technical Information AEVN2211TPMS Operating Tips AEVN2212Introduction to the Automatic Electronic Traction Aid SEVN9187Mining Trucks--Cleanliness and Component Life SEVN4142Oil Sampling--The Right Way PEVN4638

Booklets

Know Your Cooling System SEBD0518Diesel Fuels and Your Engine SEBD0717Oil and Your Engine SEBD0640Understanding The S•O•S Report TEJB1015

SERV1830 - 3 - Text Reference01/07

SUPPLEMENTAL MATERIAL (Continued)

Special Instructions

Accessing Flash Software for Machines REHS0494Caterpillar Electronic Controls Service Code Information Description List REHS0126Using the 7X1700 Communication Adapter Group SEHS9264Using the 261-3363 Wireless Communications Adapter NEHS0926Use of CE Connector Tools SEHS9065Servicing DT Connectors SEHS9615Parts Listing Of The Deutsch Connectors And Components REHS0148Use of 6V3000 Sure-Seal Repair Kit SMHS7531Use of 8T5200 Signal Generator/Counter Group SEHS8579Suspension Cylinder Servicing SEHS9411773F/775F Assembly Procedure REHS2704

Brochures

Caterpillar Electronic Technician NEHP5614Caterpillar DataView NEHP5622Diesel Engine Oil (CH4) Product Data Sheet PEHP8038How to Take a Good Oil Sample PEHP6001S•O•S Coolant Analysis PEHP5033Air Filter Service Indicator PEHP9013Cat Oil Cooled, Multiple Disc Brakes AECQ5980Caterpillar Automatic Retarder Control AEDK0075Caterpillar Truck Frames AEDK0707Mining Truck Bodies: Selecting The Right Body System For Your Job AEDK0083Caterpillar Truck Production Management System: Answering yourquestions about TPMS AEDK2953

Miscellaneous

Pocket Card "Electronic Diagnostic Codes" NEEG2500Chart "Practical Pressure Conversions" SEES5677"Cleaning Rear Axle Housing Assemblies (785/789)" SEBF8366Training CD-ROM "Caterpillar Electronic Technician (ET)for Off-highway Trucks" SERV7003Training CD-ROM "Truck Production Management System (TPMS)for Off-highway Trucks" SERV7004


TABLE OF CONTENTS

INTRODUCTION ........................................................................................................................7

MAINTENANCE .......................................................................................................................12

OPERATOR'S STATION............................................................................................................40

MONITORING SYSTEM..........................................................................................................49Messenger Display Module ..................................................................................................53Advisor/VIMS Display .........................................................................................................64

ENGINE......................................................................................................................................84Engine Electronic Control System .......................................................................................85Engine Derates......................................................................................................................95Engine Compression Brake ................................................................................................101Cooling System...................................................................................................................106Lubrication System.............................................................................................................108Fuel System.........................................................................................................................109Air Intake and Exhaust System ..........................................................................................117

POWER TRAIN .......................................................................................................................125Power Train Hydraulic System...........................................................................................127Transmission Hydraulic System .........................................................................................134Rear Axle ............................................................................................................................145Transmission/Chassis Electronic Control System ..............................................................148

STEERING SYSTEM ..............................................................................................................158

HOIST SYSTEM......................................................................................................................173

BRAKE SYSTEM ....................................................................................................................193Brake Electronic Control System .......................................................................................221Automatic Retarder Control System...................................................................................226Traction Control System.....................................................................................................228

CONCLUSION.........................................................................................................................235

VISUAL LIST ..........................................................................................................................236

HYDRAULIC SCHEMATIC COLOR CODE.........................................................................239

HANDOUTS.............................................................................................................................240

POSTTEST ...............................................................................................................................265

POSTTEST ANSWER SHEET................................................................................................269


NOTES


INTRODUCTION

Shown is the right side of a 775F Truck. The hydraulic tank is located on the right side of thetruck.

The 773F/775F Trucks come standard with oil-cooled multiple disc brakes in the rear andcaliper type disc brakes in the front.

The major features added to the 773F/775F Trucks are: the new cab, the Messenger or VIMSAdvisor monitoring system, the Tier 2 compliant C27 ACERT™ engine and cooling system, theECPC transmission, and the hydraulic brakes.

The Individual Clutch Modulation (ICM) transmission has been replaced with Electronic ClutchPressure Control (ECPC) transmission. The Chassis/Transmission Electronic Control Systemcontrols most of the same functions as on the 773D/775D Trucks.

The air system has been eliminated on the 773F/775F Trucks. The brakes are completelyhydraulic.

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773F (EED)/775F (DLS)OFF-HIGHWAY TRUCKS

INTRODUCTION

© 2007 Caterpillar Inc.

Some of the specifications of the 773F Truck are:

- Serial No. Prefix: EED - Empty weight: 45200 kg (99650 lb)- Load carrying capacity: 54.4 tonnes (60 tons)- Gross Machine Weight (GMW): 100700 kg (222000 lb)- Length: 10.33 m (33.9 ft) - Width: 5.43 m (17.8 ft)- Height: 4.5 m (14.8 ft)- Gross Power 536 kW (719 hp)- Top speed, loaded: 63.6 km/h (39.5 mph)

Some of the specifications of the 775F Truck are:

- Serial No. Prefix: DLS - Empty weight: 46198 kg (101850 lb)- Load carrying capacity: 63.5 tonnes (70 tons)- Gross Machine Weight (GMW): 109770 kg (242000 lb)- Length: 10.33 m (33.9 ft) - Width: 5.43 m (17.8 ft)- Height: 4.5 m (14.8 ft)- Gross Power 582 kW (787 hp)- Top speed, loaded: 67.5 km/h (41.9 mph)


Shown is the left side of a 775F Truck. The fuel tank is located on the left side of the truck.

2


Shown is the front of a 775F Truck. The 773F/775F Trucks use a Next Generation ModularRadiator (NGMR). Its modular design, similar to the previous folded core radiator, permitseasy removal of a single core without having to remove the entire radiator.

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Shown is the rear of a 775F Truck. The following two body options are available for the773F/775F Trucks:

- A dual-slope steel design with a "V" bottom main floor to reduce shock loading, centerthe load and reduce spills.

- The dual-slope steel body above, with the addition of a rubber liner for increasedresistance to impact and wear.

All internal wear surfaces of the truck body are made with 400 Brinell hardness steel. The steelattachment body liner is also made with 400 Brinell hardness steel. The external components ofthe body are made of steel with a yield strength of 6205 bar (90000 psi). The rubber liner isone-fifth the density of steel, but absorbs impact four times better. The rear suspensioncylinders absorb bending and twisting stresses rather than transmitting them to the main frame.

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5

MAINTENANCE

Before working on or operating the truck, read the Operation and Maintenance Manualthoroughly for information on safety, maintenance and operating techniques.

Safety precautions and Warnings are provided in the manual and on the truck. Be sure toidentify and understand all symbols before starting the truck.

The first step to perform when approaching the truck is to make a thorough walk aroundinspection. Look around and under the truck for loose or missing bolts, for trash build-up andfor coolant, fuel, or oil leaks. Look for indications of cracks. Pay close attention to high stressareas as shown in the Operation and Maintenance Manual.


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The following list identifies the items that must be serviced every 10 Hours or Daily.

- Walk-Around Inspection: Check for loose or missing bolts, leaks, trash build-up, andcracks in frame structures and body support pads.

- Back-up alarm: test- Brakes, indicators, gauges: test- Braking system: test- Coolant level- Engine air filter service indicator- Engine oil level- Fuel filter: drain water separator


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- Fuel tank: drain water/sediment- Hoist and brake oil level- Seat belt: inspect- Secondary steering: test- Steering system oil level- Transmission and torque converter oil level

The front wheel bearing oil level is checked and filled by removing the plug (1) in the center ofthe wheel bearing cover. The oil should be level with the bottom of the plug hole. The fill plugis a magnetic plug. Inspect the fill plug weekly for metal particles. If any metal particles arefound, remove the wheel cover and inspect the bearings for wear. When draining the oil, rotatethe wheel so the drain plug (2) is at its lowest position.

The service interval for changing the front wheel bearing oil is 500 hours.

Use Final Drive and Axle Oil (FDAO) or commercial FD-1. As a substitute, TransmissionDrive Train Oil (TDTO) with a commercial TO-4 may be used.

Check the tire inflation pressure. Operating the truck with the wrong tire inflation pressure cancause heat build-up in the tire and accelerate tire wear. Caterpillar recommends inflating tireswith dry nitrogen instead of air to reduce heat build-up and potential combustion. Nitrogen alsoslows rubber deterioration and rim corrosion.

NOTE: Care must be taken to ensure that fluids are contained while performing anyinspection, maintenance, testing, adjusting, and repair of the machine. Be prepared tocollect the fluid in suitable containers before opening any compartment ordisassembling any component containing fluids. Refer to the "Tools and Shop ProductsGuide" (Form NENG2500) for tools and supplies suitable to collect and contain fluidsin Caterpillar machines. Dispose of fluids according to local regulations and mandates.

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Check the front suspension cylinders for leaks or structural damage. Check the chargecondition of the front suspension cylinders when the truck is empty and on level ground.Measure the charge height of the suspension cylinders and compare the dimension with thedimension that was recorded the last time the cylinders were charged. Recharge the cylinderswith oil and nitrogen if necessary.

A grease outlet fitting (arrow) is located on one side of each front suspension cylinder. Thegrease supply fitting is located on the opposite side of the suspension cylinder. No grease outletfittings should be located on the same side of the suspension cylinder as the grease fill location.Having an outlet fitting on the same side of the suspension cylinder as the grease fill locationwill prevent proper lubrication of the cylinder.

Make sure that grease is flowing from the outlet fittings to verify that the suspension cylindersare being lubricated and that the pressure in the cylinders is not excessive.

NOTE: For more detailed information on servicing the suspension system, refer to theSpecial Instruction "Suspension Cylinder Servicing" (Form SEHS9411).

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Inspect the brake linings (1) for wear. The thickness of the brake linings (not including carrier)must not be less than 3.15 mm (.125 in). Measure the lining at both ends because one end canwear more than the other.

The clearance between the brake carrier guide pins (2) and the brake disc (3) must not be lessthan 1.5 ± 0.5 mm (.06 ± .02 in.).

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The primary fuel filter (1) is mounted between the right front wheel and the engine cooling fan.A reusable fuel/water separator mounts directly to the filter element. Periodically open thevalve (2) under the separator bowl and drain any water into an approved container.

After changing fuel filters, hold the switch (3) upward to activate the electric fuel primingpump to refill the fuel lines and filters with fuel.

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Dual engine oil filters (1) are located on the right front of the engine. Engine oil samples canbe taken at the Scheduled Oil Sampling (S•O•S) tap (2) located on the front of the oil filterbase.

The secondary fuel filter (3) is located at the right front of the engine, in front of the engine oilfilters.

A fuel filter bypass switch (4) is located on the filter base. The bypass switch provides an inputsignal to the Engine ECM indicating if the filters are restricted.

Jacket water coolant samples can be taken at the S•O•S coolant analysis tap (5). The coolanttap is located behind the engine oil filters.

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Shown are the hoist and brake hydraulic tank (1) and the torque converter and transmissionhydraulic tank (2). Both tanks are equipped with oil level sight gauges.

The oil level of both hydraulic tanks should first be checked with cold oil and the enginestopped. The level should again be checked with warm oil and the engine running.

The lower sight gauge (3) on the hoist and brake hydraulic tank can be used to check the tanklevel when the hoist cylinders are in the RAISED position. When the hoist cylinders arelowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check thehydraulic tank oil level with the upper sight gauge (4).

Check the lower converter and transmission oil sight gauge (5) with the engine off and the oilcold. Use the upper gauge (6) with the engine at idle and the oil warm.

Inspect the hoist and brake hydraulic tank breather for plugging. Remove the breather cover (7)to access the hoist and brake tank breather. The converter and transmission breather (notshown) is located at the rear of the transmission.

Inspect the condition of both hydraulic tank fill cap vents (located on top of the tanks) atregular intervals.

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When filling the hydraulic tanks after an oil change, fill the tanks with oil to the FULL COLDmark on the sight gauge. Turn on the engine manual shutdown switch so the engine will notstart. Crank the engine for approximately 15 seconds. The oil level will decrease as oil fillsthe hydraulic systems. Add more oil to the tanks to raise the oil level to the FULL COLDmark. Crank the engine for an additional 15 seconds. Repeat this step as required until the oillevel stabilizes at the FULL COLD mark.

Turn off the engine manual shutdown switch and start the engine. Warm the hydraulic oil. Addmore oil to the tank as required to raise the oil level to the FULL WARM mark.

In both tanks, use only Transmission Drive Train Oil (TDTO) with a specification of TO-4 ornewer.

The following features are provided by TDTO TO-4 oil:

- Provides maximum frictional capability required for clutch discs used in the transmission,torque converter, and brakes.

- Increases rimpull because of reduced slippage.

- Increases brake holding capability by reducing brake slippage.

- Controls brake chatter.

- Provides maximum frictional capability required for gears.


The rear axles are equipped with planetary-type final drives. Rotate the final drive until thedrain plug (1) is at the lowest position, as shown. The final drive oil level is checked and filledby removing the magnetic plug (2). The oil should be level with the bottom of the plug hole.Fill the rear axle housing with oil before filling the final drives with oil. Allow enough time forthe oil to settle in all of the compartments. This can be as much as 20 minutes during coldtemperatures. The oil is drained by removing the drain plug.

The magnetic inspection plugs should be removed weekly from the final drives and checked formetal particles. For some conditions, checking the magnetic plugs is the only way to identify aproblem which may exist.

Use FDAO (Final Drive and Axle Oil) or Transmission Drive Train Oil (TDTO) with aspecification of TO-4 or newer. These oils provide:

- Maximum frictional capability required for gears- Increased lubrication capability for bearings

NOTE: The rear axle is a common sump for the differential and both final drives. If afinal drive or the differential fails, the other final drive components must also bechecked for contamination and then flushed. Failure to completely flush the rear axleafter a failure can cause a repeat failure within a short time.

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Check the differential oil level by removing the magnetic inspection plug (1). The oil should belevel with the bottom of the fill plug opening.

Inspect the rear suspension cylinders for leaks or structural damage. Check the chargecondition of the rear suspension cylinders when the truck is empty and on level ground.Measure the charge height of the suspension cylinders, and compare the dimension with thedimension that was recorded the last time the cylinders were charged. Recharge the cylinders ifnecessary.

Inspect the condition of the rear axle breather (2) at regular intervals. The breather preventspressure from building up in the axle housing. Excessive pressure in the axle housing cancause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies.

NOTE: For more detailed information on servicing the suspension system, refer to theSpecial Instruction "Suspension Cylinder Servicing" (Form SEHS9411).

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The body up retaining pins are stored inside a cross-tube (1) in a body support beam directlyabove the retaining bracket (2). When work is to be performed while the body is raised, thebody up retaining pins must be installed through the holes in the body retaining bracket and therear frame support (3) to hold the body in the raised position. The body is shown in thelowered position.

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The fuel tank is located on the left side of the truck. The fuel level sight gauge (1) is used tocheck the fuel level during the walk around inspection. A fuel level sender is located on thefuel level sight gauge. The fuel level sender provides input signals to the monitoring system,which informs the operator of the fuel level.

Open the drain valve below the tank to remove condensation and sediment from the fuel tank.

Inspect the condition of the fuel tank breather (above tank) and the fuel fill cap (2) at regularintervals.

Fuel can be added at the attachment quick service fuel fill connector (3).

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The torque converter and transmission charging filter (1) is mounted to a bracket on the outsideof the left frame rail in front of the fuel tank.

Torque converter and transmission oil samples can be taken at the S•O•S tap (2).

The oil filter bypass switch (3) provides input signals to the Transmission/Chassis ECM. TheECM sends a signal to the monitoring system in the cab to warn the operator when the filter isrestricted.

A pressure test port (4) is available for monitoring charge pressure for the torque converter andtransmission circuits.

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The brake oil filter (1) is mounted to a bracket on the inside of the left frame rail. The brakefilter includes an oil filter bypass switch (2) which provides input signals to the Brake ECM.An S•O•S port (3) can be accessed from below the machine.

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Before climbing the truck ladder, make sure that the manual engine shutdown switch (1) isOFF. The switch is located below the cab at the base of the left stairway.

The engine will not start if the manual shutdown switch is ON. If necessary, the switch can beused to stop the engine from the ground level.

The access light switch (2) is used to turn on or turn off the lighting in the area around thestairs. There is a second access light switch on the left side of the dash in the cab.

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While climbing the ladder, make a thorough inspection of the radiator. Be sure that no debrisor dirt is trapped in the radiator cores.

The battery disconnect switch is located under a cover (1) at the bottom of the right accessladder. If the machine is being parked for an extended period (overnight, etc.) turn off thedisconnect switch and remove the key.

The machine lockout and engine lockout switches are located behind an access cover (2)between the radiator cowling and the right stairway.

The batteries are located inside the front bumper (3), at the base of the radiator cowling.Inspect the battery connections for corrosion or damage. Keep the battery terminals clean andcoated with petroleum jelly.

Inspect the electrolyte level in each battery cell, except maintenance free. Maintain the level tothe bottom of the fill openings with distilled water.

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This illustration shows the engine disconnect switch (1) and the auxiliary start receptacle (2).

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The engine lockout control switch (1) allows the engine to be safely locked out while service isperformed. The engine must be stopped to activate the engine lockout mode. When the enginelockout mode is activated, the following conditions exist:

- The engine starter is disabled.

- The secondary steering is disabled.

- The prelube function is disabled.

The following conditions must be met before the engine lockout mode will activate:

- The transmission control must be in the PARK position.

- The engine must be OFF.

When the switch is activated, one of the following results will occur:

- The indicator lamp (2) will illuminate continuously to indicate that the machine is in theengine lockout mode.

- The indicator lamp will flash to indicate that the engine lockout mode will not activateuntil the transmission control is in the PARK position and the engine is OFF.

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The machine lockout control switch (3) allows the machine to be safely locked out whileservice is performed. When the machine lockout mode is activated, the following conditionsexist:

- The engine will start.

- The transmission is disabled.

- The hoist is disabled.

- The steering is disabled.

- The machine lockout mode indicator (4) will illuminate only after the start key is turnedon.

NOTE: The lockout mode indicator on the dash panel will illuminate when the enginelockout control or the machine lockout control is activated.

Also located near the lockout switches are the following circuit breakers:

- 90 Amp Alternator (5)

- 15 Amp Engine (6)

- 80 Amp Starter Solenoid (7)


The coolant level on the 773F/775F is checked with the jacket water coolant sight gauge (1)located below the cab on the right side of the front cowling. Coolant is added by removing theradiator cap (2) located inside an access door on the upper deck.

The water used in the cooling system is critical for good cooling system performance. Usedistilled or deionized water whenever possible to prevent acids or scale deposits in the coolingsystem. Acids and scale deposits result from contaminants that are found in most commonwater sources.

Never use water alone. All water is corrosive at engine operating temperatures without coolantadditives. Also, water alone has none of the lubrication properties that are required for waterpump seals.

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Cat trucks are filled at the factory with Extended Life Coolant (ELC). If ELC is maintained inthe radiator, it is not necessary to use a supplemental coolant additive. Do not use aconventional coolant to top-off a system filled with Cat ELC.

An acceptable substitute for ELC is a Cat DEAC (Diesel Engine AntiFreeze/Coolant) or acommercial heavy-duty coolant/antifreeze that meets ASTM D4985 or ASTM D6210specifications.


The steering system hydraulic tank is located on the right platform.

Check the steering system oil level at the sight gauge (1), on the side of the tank.

The steering system oil filter (2) cleans the oil before it enters the hydraulic tank.

The steering system uses a pressure compensated piston-type pump mounted to the rear of theengine. Case drain oil from the steering pump returns to the steering tank through a case drainfilter (3).

Before removing the fill cap (4) to add oil to the steering system, depress the pressure releasebutton (5) on top of the breather to release any pressure from the tank.

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The steering system filter base and the case drain filter base have bypass valves that allow thesteering oil to bypass the filters if they are plugged.

The engine oil level dipstick (6) and the engine oil fill tube (7) are located inside the accesscover next to the steering oil tank. Check the engine oil level with the dipstick and add engineoil at the fill tube.

Caterpillar recommends multigrade Diesel Engine Oil (DEO) with a specification of ECF-1.API CH-4, CI-4, and CI-4 Plus oils are only acceptable if they meet ECF-1 specifications.

DEO oils with a CG-4 specification are acceptable, but should be limited to 250-hour oilchange intervals. CF and older oils should not be used in Caterpillar diesel engines.

Cat ECF-1 Specification was established by Caterpillar in 2003 and requires excellent sootdispersion, wear control, and piston deposit control.


Shown are the air intake system components. Check the air filter restriction indicators (1). Ifthe yellow piston is in the red zone, the air filters are restricted and must be serviced.

The air filter housing covers serve as the precleaner assemblies. When servicing the filterelements, clean the precleaners (2) and dust valves (3) using air or water pressure, or detergentwash.

The dust valve is OPEN when the engine is OFF and closes when the engine is running. Thedust valve must be flexible and closed when the engine is running or the precleaner will notfunction properly and the air filters will have a shortened life.

Two filter elements are installed in the filter housings. The large element is the primaryelement and the small element is the secondary element.

Air intake system tips:

- The primary element can be cleaned a maximum of six times.

- Never clean the secondary element for reuse. Always replace the secondary element.

- Air filter restriction causes black exhaust smoke and low power.

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To check the fluid level of the windshield washer reservoir, open the access door located at theleft rear of the cab, behind the cab door. Open the filler cap (1) to check the fluid level and fillas necessary.

To the left of the filler spout is the air conditioner filter (2). Clean or replace the filter elementwhen a reduction of circulation in the cab is noticed.

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The remaining 10 Hours or Daily checks are performed in the operator's compartment:

- Brakes: Check operation

- Indicators and gauges: Test operation

- Seat belt: Inspect

- Back-up alarm: Test operation

- Secondary steering: Test operation

The service brakes are checked by depressing the pedal (1) and placing the shift lever in FIRSTFORWARD. Accelerate the engine until the truck moves. The truck must not move below1200 rpm. This procedure should be repeated to test the secondary brakes by depressing thesecondary brake pedal (2).

The cab air filter (3) is located inside the cab door, in the left-rear corner behind the trainer seat.Clean or replace the cab fresh air filter when necessary.

NOTE: Refer to the Operation and Maintenance Manual for information on theremaining tests performed in the cab.

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This illustration shows the cab air filter (1) located behind the trainer seat (2).

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OPERATOR'S STATION

Shown is a view of the 773F/775F operator compartment. The operator's station for the773F/775F has been changed to improve operator comfort and ergonomics. The operator seat(1) is centered in the cab with the trainer's seat (2) positioned to the left.

The hoist control lever (3) is now on the right console next to the transmission control lever (4).

The 773F/775F is equipped with a standard Messenger Monitoring System or optionalVIMS/Advisor Monitoring System (shown).

The optional Caterpillar Work Area Vision System (WAVS) is a closed circuit video monitoringsystem. WAVS consists of a 178 mm (7 inch) LCD color display (5) and may include one, two,or three cameras. The display is mounted in the machine cab. The cameras are mounted on theframe of the machine. The location of the camera(s) is dependent on the machine type.

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The Truck Production Management System (TPMS) on the 773F/775F is controlled by a TPMSECM if the machine is equipped with Messenger or a VIMS ECM if the machine is equippedwith VIMS/Advisor. There are two sets of TPMS external loading lamps on the truck. One setof lamps is on the left side of the cab (arrow) and the other set is on the right platform. Thelamps are green and red. The lamps inform the loader operator of the loading progress towarda target payload weight. The lamps are active only during the loading cycle and are off at allother times.

During loading, the green (continue loading) lamps will be ON until the payload is 95% of thetarget weight setting. Then, the red (stop loading) lamp will light. A "last pass" indication canbe programmed into the system. With last pass indication, the TPMS calculates an averageloader pass size and predicts payload weight. If the predicted weight after the NEXT loaderpass will be above 95% of the target weight setting, the red lamps FLASH. The red lamps willbe ON continuously after the last pass (when fully loaded). A minimum of three loader passesare required for the "last pass" indication option to function correctly. The actual measuredweight of the material in the truck body is displayed on the Messenger display or theVIMS/Advisor display.

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Located on the left side of the front dash panel are:

- Telescopic/tilt steering column adjustment lever (1): Push for telescoping and pull for tilt.

- Intermittent wiper/washer, turn signal control and dimmer switch (2).

- Steering wheel mounted electric horn control (3).

- Light switches and hazard warning switch (4).

The instrument panel (5) includes a tachometer, four gauges, and several indicators that displaythe machine systems status. An LCD screen displays the service hour meter, machine groundspeed, actual gear, and direction.

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5

Located on the right side of the steering column is the retarder lever (1). The retarder lever isused to modulate engagement of the service brakes. The retarder lever engages the rear brakes.The retarder lever can control the modulation of the service brakes more precisely than theservice brake pedal located on the cab floor.

Located on the dash to the right of the retarder lever are the key start switch (2), fan speedswitch (3), temperature variable knob (4), air conditioner switch (5), and cigarette lighter (6).Above the HVAC controls is the Messenger display (7).

Switches to the left of the Messenger display are the ARC ON/OFF switch (8), compressionbrake switch (9) (if equipped), and front brake switch (10).

36


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To the right of the operator's seat is the shift console which contains the transmission shift lever (1) and the hoist control lever (2). The 773F/775F truck has SEVEN speeds FORWARDand ONE REVERSE.

The top gear limit and body up gear limit are programmable through the Transmission/ChassisECM. The top gear limit can be changed from THIRD to SEVENTH. The body up gear limitcan be changed from FIRST to THIRD.

The 773F/775F truck hoist system is electronically controlled. The hoist control lever activatesthe four positions of the hoist control valve. The four positions are: RAISE, HOLD, FLOAT,and LOWER.

A fifth position of the hoist valve is called the SNUB position. The operator does not havecontrol over the SNUB position. The body up switch controls the SNUB position of the hoistvalve. When the body is lowered, just before the body contacts the frame, theTransmission/Chassis ECM signals the hoist solenoids to move the hoist valve spool to theSNUB position. In the SNUB position, the body float speed is reduced to prevent hard contactof the body with the frame.

The truck should normally be operated with the hoist lever in the FLOAT position. Travelingwith the hoist in the FLOAT position will make sure the weight of the body is on the frame andbody pads and not on the hoist cylinders. The hoist valve will actually be in the SNUBposition.

37


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If the transmission is in REVERSE when the body is being raised, the hoist lever sensor is usedto shift the transmission to NEUTRAL. The transmission will remain in NEUTRAL until:

1. the hoist lever is moved into the HOLD or FLOAT position; and

2. the shift lever has been cycled into and out of NEUTRAL.

The hoist lever is also used to start a new TPMS cycle.

NOTE: If the truck is started with the body raised and the hoist lever in FLOAT, thelever must be moved into HOLD and then FLOAT before the body will lower.

The throttle backup and throttle lock switch (3), the WAVS alternate camera system switch (4)(if equipped), and a 12V power port (5) are also located on the shift console.


The overhead console can be equipped with three switches. The optional heated mirrors switch (1) controls the heated mirrors.

The TCS test switch (2) is used to perform the TCS test when the switch is held.

The brake release/secondary steering switch (3) manually activates the brake release andsecondary steering pump when the switch is held.

38


1 2 3

Located on the floor of the cab are the following pedals:

- Secondary brake pedal (1): Used to modulate application of the parking brakes on therear wheels. A position sensor is attached to the secondary brake pedal that providesinput signals to the Brake ECM.

- Service brake pedal (2): The service brake pedal is used to modulate engagement of theservice brakes on all four wheels if the front brake ON/OFF switch is in the ON position.A position sensor is attached to the service brake pedal that provides input signals to theBrake ECM.

- Throttle pedal (3): A throttle position sensor is attached to the throttle pedal. The throttleposition sensor provides the throttle position input signals to the Engine ECM.

39


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Located behind the trainer's seat are the fuse panels (1), the Cat ET service port (2), the TPMSor VIMS service port (3), the Product Link service port (4), a 12V power receptacle (5), and the 20 amp heater/air conditioner fan circuit breaker (6).

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MONITORING SYSTEM

The monitoring system on the 773F/775F Off-highway Trucks monitors various machinesystems and then conveys the machine status to the operator. The 773F/775F can be equippedwith the standard monitoring system which includes a Messenger display module, or theoptional monitoring system which includes a VIMS/Advisor display module.

Both monitoring systems include an instrument cluster. The instrument cluster is a cab displaythat shows the operator the status of various machine parameters and alerts the operator ofspecific machine conditions.

The ECMs and monitor display modules communicate over the Cat Data Link. The displaymodules communicate with the instrument cluster over the Can Data Link.

The monitoring system receives information from machine switches and sensors via the ECMsshown in this illustration of the Machine Electronic Control System.

The 773F/775F can also have the following attachments: Minestar, RAC, Product Link,Inclinometer, Telemetry antenna, and GPS antenna.


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The instrument cluster (1) and optional VIMS/Advisor display panel (2) are shown is thisillustration. The standard Messenger module (not shown) is installed in the same location asthe VIMS/Advisor display panel.

Problems from the machine systems are classified into four warning categories (1, 2, 2S, and 3)similar to other Caterpillar monitoring systems.

During the normal operation mode and the menu mode, the Messenger or VIMS/Advisordisplay may be interrupted by a warning message. Warning messages are displayed whenimportant instructions or information need to be displayed.

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Shown is the Instrument Cluster located in the center of the front dash panel. The InstrumentCluster includes 18 dash indicators, five analog gauges, and an LCD digital display (1). TheLCD display window in the lower center of the dash includes the truck speed, gear, anddirection on the top of the display and the service hour meter on the bottom of the display.

The five parameters monitored by the analog gauges are:

- Brake oil temperature (2)

- Engine coolant temperature (3)

- Engine speed (4)

- Torque Converter oil temperature (5)

- Fuel Level (6)

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This illustration shows the gauges and indicators on the instrument cluster.


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Messenger Display Module

The standard Messenger display module (1) is located in the right side of the front dash. Thepurpose of the Messenger is to display relevant machine information to the operator or servicepersonnel. The Messenger display is used in conjunction with the instrument cluster to act asthe monitoring system for the machine.

The Messenger has a menu structure that allows the user to access the desired machineinformation. The default screen will display under normal machine operating conditionswithout any intervention from the operator or service personnel.

The default screen of the Messenger module shows the shift lever and the gear position. Thedefault screen is displayed at machine start-up and until the operator or the technician navigatesto another screen.

The Messenger consists of the display and four navigation buttons that are used to navigatethrough the menu structure. The button functions from left to right are as follows:

Back (2): Used to navigate to the previous screen that was accessed in the Messenger.

Left/Up (3): Allows the user to scroll left or up. Scroll direction is dependent on thespecific data that is being displayed on the screen.

Right/Down (4): Allows the user to scroll right or down. Scroll direction is dependent onthe specific data that is being displayed on the screen.

OK (5): Acts as a confirmation function for the Messenger.

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The Messenger Menu screen is divided into three sections. The top section identifies the nameof the current menu. If the current name is split by a colon ":" then this indicates that the nameafter the colon ":" is the current menu and the name before the colon ":" is the parent menu ofthe current menu. The center section displays the current menu option that can be selected bypressing the OK button. The arrows at the left of the screen indicate whether you can scroll tothe next screen to see further menu options.

There are a total of five main menus that are available for navigation. Only one menu can bedisplayed at a time. The menus are accessed from the default menu by pressing the back arrowbutton. The five menus are:

- Performance

- Totals

- Settings

- Service

- Service mode


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This illustration of a performance screen submenu shows the engine coolant temperature andshift lever position.

A typical Messenger information screen normally displays the information in pairs. Theheaders at the top of the screen identify the information. The current values are displayedbelow the headers. The arrows at the left of the screen indicate whether you can scroll to thenext screen to see additional information.

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The Performance menu allows the operator or technician to view two pages of information.These pages of information monitor vital machine system data during machine operation. Thisinformation can only be viewed. The Performance menu uses two screens to show the real timestatus of the information listed above on the right side of the illustration.


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The Totals main menu allows the operator or the technician to access information about themachine systems. The totals data can be used to determine when scheduled maintenance isrequired.

The Totals menu shows accumulated values and includes two submenus. The two submenusare Payload and Machine.

The Payload and Machine submenus display the information listed on the right side of theabove illustration.


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Parameters are normally adjusted for specific operating conditions, operator preferences, andmachine operating efficiency. The machine setup affects the parameters that are displayed. Theattachments that are on the machine determine the software that is contained in the ECMs.Messenger looks at the software versions to determine the parameters that will be displayed andthe parameters that will be variable.

NOTE: Cat ET can also be used to access the parameters.

The Settings menu allows the user to adjust the parameters for the following:

- Messenger Display

- Machine Identification

- Transmission Operation

- Brake Operation

- Payload Operation

- Engine Operation

50


The Messenger Display parameters relate to the operator’s preferences for the Messengerdisplay. The following parameters may be adjusted:

- Language: Six standard languages (other languages available).

- Units: Metric or English.

- Contrast: Screen contrast.

- Headlights On: Screen brightness with headlights ON.

- Headlights Off: Screen brightness with headlights OFF.

The Machine settings allow the user to set the machine serial number. The followingparameters may be adjusted:

- Product ID: Allows the user to set the machine serial number (password protected).

- Equipment ID: Allows the name of the truck to be changed (password protected).

The Transmission setting allows the following parameters to be adjusted:

- Top Gear Limit: Allows the user to set the highest gear performance level.

- Body Up Gear Limit: Adjusts the gear limit during truck operation when the body israised.

- Machine Speed Limit: Sets the highest truck speed.

- Fuel Economy Mode: Allows the fuel usage to be changed.

- Machine Overload Speed Limit: Limits transmission gear and engine speed whenexcessive payloads are detected (if machine is equipped with TPMS).

The Brake setting allows the user to set the desired ARC speed and is password protected.

The Payload menu allows the configuration of the Payload settings and is password protected.The Payload settings include the following:

- Target Payload: Read and program the truck target payload.

- Overload Limit: Read and program the percent overload.

- Green TPMS Lamp: Read and program the installation of the green TPMS lamp.

- Red TPMS Lamp: Read and program the installation of the red TPMS lamp.

- Last Pass Enabled: Read and program the installation of the Last Pass indicator. TheLast Pass indicator informs the shovel operator of the last load before the payload is overthe rated load.

The Engine setting allows the user to change the ether solenoid configuration to "No EtherSolenoid Installed" or "Continuous Flow" and is password protected.


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The Service menu allows the technician to access the machine parameters. The technician mayalso make selections for viewing or clearing logged events or codes.

The Service menu will allow the technician to view data for the following systems: brake,steering, implement, and power train. The status of electronic components in the machine’smajor systems can also be viewed. The Service menu option is displayed by selecting Servicefrom the Main Menu. Press the Left/Up arrow button or the Right/Down arrow button untilService is displayed. Then press the OK button. The Service menu contains the following sixsubmenus:

- Diagnostic Events: Displays a complete list of all active and inactive event codes anddiagnostic codes.

- System Parameters: Allows the technician to view the status of system components.

- Calibrations: Allows the technician to perform a payload calibration. The payloadsystem must be calibrated if new TPMS software is installed or the suspension is charged.

- System Tests: Allows the user to perform a transmission stall test or a system self test onthe machine.

- Systems Information: Allows the user to display information on all of the ECMs installedon the machine, such as ECM Part Number, etc.

- Tattletale: The Messenger display module records the extreme value for each conditionof the machine that is monitored.

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These illustrations show the information available within the Diagnostic Events menu.

From the Service menu, use the appropriate arrow button to highlight the Diagnostic Eventsoption and press the OK button to access the Diagnostic Events. Select the View Diagnosticsdisplay by pressing the OK button. The View Diagnostics option will display a complete list ofcodes (bottom left illustration). Each line on the list will show the following information:

- SRC (Source ID)

- CODE

- OCC (Number of occurrences of the event or code)

- ACT (if the code is active or inactive).

Use the appropriate arrow button to highlight a diagnostic code or an event code on the list.Press the OK button to display the codes Detailed View (bottom right illustration). TheDetailed View will display a text message that shows the following information: reportingECM, failed component code, and explanation of the event.

The technician can clear logged codes one at a time. Active codes are indicated with a markunder the "ACT" column. Active codes cannot be cleared until the faults have been corrected.To clear a code, access the Detailed View of the code, press the OK button and follow theprompts and directions.

NOTE: Only Level I and Level II codes may be cleared with Messenger. When a codeis cleared from Messenger, the memory from the reporting ECM is cleared. The code isnot cleared from the Messenger ECM. Once the code has been cleared from thereporting ECM, Messenger will update the code list. Messenger is an interface betweenthe technician and the machine ECMs.


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The Service Mode Password menu is used to enter the Service mode. The Service ModePassword protects certain features from access by the operator. Features that need to beprotected from the operator can be enabled or disabled with a password.

NOTE: For more information on the Messenger Monitoring System, refer to the 773F,775F, 777F Off-highway Truck Monitoring Systems Operation, Troubleshooting, Testing,and Adjusting Service Manual module (RENR8344).

53


Advisor/VIMS Display

Shown above is the Advisor/VIMS graphical display module. It is located on the right side ofthe dash. It is the operator and technician’s interface with the Advisor Monitoring System,including VIMS. Information is displayed on a backlit LCD display screen.

The top portion of the screen is called the "Top Banner" and it displays vital machineinformation at all times. The Top Banner may display different information from machine tomachine, depending on the model and the attachments that are installed.

At the right of the display screen is a column of five user interface buttons. These buttons areused to navigate through the numerous Advisor screens, to make menu selections, or to enterdata. The five buttons, from top to bottom, are:

- LEFT/UP Arrow Button (1) - This button is used for screen navigation or data entry. It can beused:

• to scroll up a vertical list or scroll left across a horizontal list;

• to decrease a setting value, such as decreasing brightness/contrast.

- DOWN/RIGHT Arrow Button (2) - This button is also used for screen navigation or dataentry. It can be used:

• to scroll down a vertical list or scroll right across a horizontal list;

• to increase a setting value, such as increasing brightness/contrast.

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- BACK Button (3) - This button is used:

• to go up one level in a stair-step (hierarchical) menu structure, or to return to theprevious screen;

• as a backspace, or cancel key when the operator or technician wishes to delete enteredcharacters.

- HOME Button (4) - This button is used to return to the home menu screen, regardless of whatscreen is currently displayed.

- OK Button (5) - This button is used:

• to make selections from a screen;

• to confirm an entry, such as a password, or for saving an operator profile entry.

Navigation through the menus and sub-menus is accomplished by using the ARROW Buttonsto highlight the desired selection, then pressing the OK Button. The ARROW Buttons are alsoused to highlight a mode or to set a parameter. Pressing the OK Button selects that option.

NOTE: The left buttons are used to display a screen without scrolling. If a screen isselected and one of the left buttons is pressed and held for at least three seconds, thescreen is saved (programmed). Whenever the button is pressed again the "saved"screen will appear.


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Upon machine start-up (key ON), an introduction screen appears as shown in the topillustration and Advisor performs a self-test routine. After a few seconds the main screen willappear as shown in the bottom illustration.

NOTE: The time and date are set with VIMSpc software.

Also displayed to the right of the time and date is the inclinometer value.

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The illustration above shows a "pop-up" warning screen generated by the Transmission/ChassisECM and reported by Advisor. There may be more warning screens if there are any otheractive faults or events reported to Advisor by the Transmission/Chassis ECM, or any otherECM on the machine. Advisor will scroll through all of the warning screens generated by all ofthe active faults and events. Each of these warning screens must be individually acknowledgedby pressing the "OK" button.

Each of these warning screens contains the following information:

- The reporting ECM (in text)

- The reporting MID (module identifier, or ECM code)

- The ID (Component ID and Failure Mode Identifier)

- A text message stating the failed component

- A text message stating the failure mode of the component

- A prompt for the operator to acknowledge the warning

Acknowledging these warnings does not clear them from the reporting ECM's memory, butonly clears them from the screen, or "snoozes" them. The warnings remain an active event orfault until the problem is resolved. Advisor will display the message again after a pre-determined amount of time, depending on the severity of the event.

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Advisor’s menu structure is arranged in a stair-step, or hierarchical list format. When theoperator or technician selects an option from a menu or list, the resulting screen is one leveldown from that selection. More selections, or options, may be available from that screen aswell. There may also be more than one page of information or options to be displayed fromany level. This is indicated by the "More Options" icon, which may point left, point right, pointup, or point down, depending upon how the data or list is arranged.

The illustration above shows the options that are available from Advisor's Home Menu screen.The Home Menu screen and its options will be displayed upon pressing the HOME button fromany screen within Advisor.


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The Operator menu allows the user to perform the following:

- Select a profile

- Create a profile

- Delete a profile

- View/save a current profile

- Factory Set (recalls default settings)

The profile of an operator is a saved set of preferences that is identified by a name. Once theprofile is created, the operator may associate various display settings and settings for the powertrain to that profile. After all of the parameters have been adjusted to the operator's preference,the operator may then save the parameters for future use.

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This illustration shows the options within the Operator Menu.


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The Service menu contains six submenus. The following is a list of the submenus:

- Diagnostics

- Calibrations

- System Information

- Tattletale

- System Tests

- Service Parameters

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This illustration shows the diagnostics submenu within the service menu.

The Active Events menu option shows the ECM and the service hours for each event. Thefollowing list is of information that is displayed for the active event:

- Electronic Control Module

- Event Code

- Date of occurrence

- Time of occurrence

- Warning Level

- Number of occurrences

The Logged Events menu option shows the list of events and diagnostic codes that have beenrecorded. Logged events can only be cleared by downloading and resetting the VIMS ECMwith VIMSpc.

The Trigger Snapshot menu option allows the user to manually initiate a snapshot of the systemin addition to the snapshots that are already programmed. The snapshot will remain active untilthe time has elapsed.

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The Data Logger Start menu option allows the user to initiate the data logger. If theinformation for the data logger is being downloaded from the machine, the data logger cannotbe started. The operator can initiate and stop the data logger numerous times until the totaltime for logging the data is thirty minutes.

The Data Logger Reset menu option allows the user to reset the data logger, which clears all ofthe logged information. Thirty minutes will be available after the data logger has been reset.

NOTE: The Data Logger is the only onboard file that can be reset through the Advisordisplay. The Advisor must be either in the Service Mode or Cat ET must be connectedto the data link to reset the data logger. The VIMSpc software is not needed to reset thedata logger.


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These illustrations show four of the submenus within the service menu.

The Calibrations option consists of the Truck Payload and Inclinometer calibrations.

The System Information menu option allows the user to view the information for the followingmachine ECMs:

- Advisor

- Engine

- Transmission/Chassis

- Brake

- VIMS

The ECM information contains the following:

- ECM serial number

- Software part number

- Software release date

- Software description

The following options are available under the tattletale menu:

- Active

- Brake Oil Temperature

- Engine Coolant Temperature

- Engine Speed

- Torque Converter Temperature

- Fuel Level

The Active option will display the tattletale value for each gauge. The five specific options willdisplay the tattletale value for the gauge that is specified.

NOTE: The tattletale is password protected. The value for each gauge is protectedfrom being cleared.

The System Tests option will allow the technician to perform the Stall Diagnostic Test or theSelf Test.

The instrument cluster will initiate a self test when the key start switch is moved to the STARTposition. The gauge needles will move to the maximum right position for 0.5 seconds and thenreturn to the minimum left position. This action prevents the gauge needles from circling to thebottom side of the gauge if the display is inverted.


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This illustration shows the Service Parameters submenu within the service menu.

The following Service Parameters options will be displayed:

- Sort By ECM

- Sort By Type

- All Parameters

The Sort By ECM menu option allows the user to view the parameters that are associated witheach ECM. All of the parameters for the specific ECM are listed. The following ECMs can beselected:

- Advisor

- Engine


- Brake

- VIMS

66


The Sort By Type menu option allows the user to view the parameters that are associated withdifferent components. The following types of parameters can be chosen:

- Temperatures

- Pressures

- Speeds

- Filter Switches

- Operator Inputs

- Sensor Duty Cycles

- Totals

The All Parameters menu option allows the user to view the entire list of parameters.


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The Settings menu allows the user to view the following parameters which are the sameparameters as the Messenger Settings menu:

- Display Setup

- Machine


- Brake

- VIMS (same as Messenger Payload submenu)

- Engine

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The Display Setup parameters relate to the operator’s preferences for the Advisor display. Thefollowing parameters may be adjusted:

- Language (same as Messenger)

- Units (same as Messenger)

- Contrast (same as Messenger)

- Headlights On (same as Messenger)

- Headlights Off (same as Messenger)

- Date format: (Advisor only)

- Time format: (Advisor only)

The Machine setting allow the user to set the machine serial number. The following parametersmay be adjusted and are the same as the Messenger Display:

- Product ID

- Equipment ID

The Transmission/Chassis setting allows the following parameters to be adjusted:

- Top Gear Limit (same as Messenger)

- Body Up Gear Limit (same as Messenger)

- Machine Speed Limit (same as Messenger)

- Fuel Economy Mode (same as Messenger)

- Machine Overload Speed Limit (same as Messenger)

- Load Count (Advisor only)

The Brake setting is the same as the Messenger display.

The VIMS/Payload menu allows the configuration of the Payload settings and is passwordprotected. The following payload settings are the same as the Messenger Display:

- Target Payload

- Overload Limit

- Green TPMS Lamp

- Red TPMS Lamp

- Last Pass Enabled

The Engine setting allows the user to change the ether solenoid configuration to "No EtherSolenoid Installed" or "Continuous Flow" and is the same as the Messenger Display.


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The Payload menu option is entered by selecting Payload from the Main menu. The Payloadmenu option allows the user to view the information for the payload. The user can view thefollowing information:

- Target for the payload

- Calculated gauge for the payload

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The Monitor menu option allows the user to view four parameters. The navigation button isused to select the parameter or view a different parameter. Press the OK button to obtain a listof available parameters.

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The Grade menu option allows the user to view the grade of the hill. The user can view thefollowing information:

- Percentage of the grade value

- Image of the truck that represents the grade

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The Service Mode menu option allows the user to enable and disable the service mode. Thepassword entry screen will appear if the password has been entered in Cat ET. The Advisorwill enter the Service Mode after the password has been entered correctly.

NOTE: For more information on the Advisor/VIMS Monitoring System, refer to the773F, 775F, 777F Off-highway Truck Vital Information Management System (VIMS)Systems Operation, Troubleshooting, Testing, and Adjusting Service Manual module(KENR5955).

75

76


ENGINE

Shown is the C27 engine with ACERT™ Technology used in the 773F/775F Off-HighwayTrucks.

77


The engine performance specificationsfor the 773F Truck are:

Serial No. Prefix: EHXPerformance Spec: 0K5975Gross Power: 536 kW (719 hp)Full Load rpm: 2000High Idle rpm 2200Low Idle rpm 800Max Torque rpm 1300Overspeed rpm 2800

The engine performance specificationsfor the 775F Truck are:

Serial No. Prefix: LJXPerformance Spec: 0K5979Gross Power: 587 kW (787 hp)Full Load rpm: 2000High Idle rpm 2200Low Idle rpm 800Max Torque rpm 1300Overspeed rpm 2800

This V-12 engine uses twin turbochargers, Air to Air AfterCooler (ATAAC) and MechanicalElectronic Unit Injection (MEUI) for power, reliability and fuel economy. The C27 iscompliant with U.S. EPA Tier 2 and European Union Stage II emissions regulations.

78

Engine Electronic Control System

Shown is the electronic control system component diagram for the C27 engine used in the773F/775F Truck. Fuel injection is controlled by the Engine Electronic Control Module(ECM).

Many electronic signals are sent to the Engine ECM by sensors, switches, and senders. TheEngine ECM analyzes these signals and sends signals to various output components. Outputcomponents can be relays, lamps, other controls, or solenoids.

For example, based on the various input signals, the Engine ECM determines when and for howlong to energize the injector solenoids. When the injector solenoids are energized determinesthe timing of the engine. How long the solenoids are energized determines the engine speed.


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Fuel injection and some other systems are controlled by the Engine ECM (1) located at thefront of the engine. Other systems controlled by the Engine ECM are: ether injection, enginestart function, engine oil pre-lubrication, variable speed Rockford fan, engine retarding, andengine derate.

The Engine ECM has two main connectors for diagnostics. The larger 120-pin connector (2)known as J2 connects to the engine harness. The smaller 70-pin connector (3) is identified onschematics as J1 and connects to the machine harness.

A 2-pin timing calibration connector is located to the right of the ECM. If the engine requirestiming calibration, a timing calibration sensor (magnetic pickup) is installed in the flywheelhousing and connected to the timing calibration connector.

Using the Caterpillar ET (Cat ET) service tool, timing calibration is performed automaticallyfor the speed/timing sensors. This step is performed to avoid instability and ensures that nobacklash is present in the timing gears during the calibration process. Timing calibrationimproves fuel injection accuracy by correcting for any slight tolerances between the crankshaft,timing gears, and timing wheel. Timing calibration is normally performed after ECMreplacement, cam or crank sensor replacement, or timing wheel replacement.

Occasionally, Caterpillar will make changes to the internal software that controls theperformance of the engine. These changes can be performed by using the WinFlash program inCat ET. Cat ET is used to diagnose and program the electronic controls used in Off-highwayTrucks. If using the WinFlash program, a "flash" file must be obtained from Caterpillar anduploaded to the ECM.

79


12

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The coolant temperature sensor (1) is located on top of the engine toward the front left side.The coolant temperature sensor is an analog sensor that is monitored by the Engine ECM.When the coolant temperature is too high, the Engine ECM will signal the monitoring system todisplay a warning.

The Engine ECM also uses the coolant temperature sensor information for cold mode functionssuch as timing changes, elevated idle, cold cylinder cut-out, and ether injection.

The intake air temperature sensor (2) is located on top of the engine toward the front right side.The intake air temperature sensor is an analog sensor that is monitored by the Engine ECM.The ECM monitors intake air temperature for derating the engine at high temperatures, forengine shutdown at high temperatures, and for signaling the monitoring system in the event of aproblem.

NOTE: If a high temperature event is severe enough, the monitoring system will issue aLevel 3 warning. The operator must park the machine as soon as possible. When theEngine ECM determines that the ground speed is zero and the transmission is in PARK,the engine will automatically shut down.

The turbo outlet pressure sensor (3) is used for calculating boost.

The atmospheric pressure sensor (4) is located on top of the engine toward the front right side.The atmospheric pressure sensor is an analog sensor that is monitored by the Engine ECM.The ECM monitors atmospheric pressure for the following: altitude derate, air inlet restrictionderate, and calibration reference for other sensors.

80


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The crankshaft speed/timing sensor (1) is located on the lower left of the engine toward thefront side. The crank sensor measures engine speed and timing for control of the timing anddelivery of fuel to each of the engine's cylinders. Sensing engine speed allows engine speedgoverning, fuel limiting, and fuel injection timing. If the crank speed/timing sensor fails, thecam speed/timing sensor allows for continuous operation.

The oil pressure sensor (2) is located on the left side of the engine. The oil pressure sensor isan analog sensor that is monitored by the Engine ECM. When the oil pressure is too low, theEngine ECM will signal the monitoring system to display a warning. The ECM will also log anevent that requires a factory password to clear.

81


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The cam speed/timing sensor (arrow) is located on the right side of the engine at the back of thetiming gear housing behind the primary fuel filter. The cam sensor is used as a back-up for thecrank speed/timing sensor. If the crank speed/timing sensor fails, the cam speed/timing sensorallows for continuous operation.

82


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The engine will start and run when only one sensor signal is present from either the crank orcam sensor. During engine operation, if both speed/timing sensors fail, the Engine ECM willstop fuel injection and the engine will shut down. During start-up, the loss of both sensors willprevent the engine from starting.

If the engine is running and the signal from the crank speed/timing sensor is lost, a slightchange in engine performance will be noticed when the Engine ECM performs the changeoverto the cam speed/timing sensor. If the signal from the crank speed/timing sensor is not presentduring start-up, the engine will start normally.

Loss of the cam speed/timing sensor during engine operation will not result in any noticeablechange in engine performance. However, if the signal from the cam speed/timing sensor is notpresent during start up, the engine may require a slightly longer period of time to start and mayrun rough for a few seconds until the ECM determines the proper firing order by using only thecrank engine speed/timing sensor.


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The teeth configuration in the crankshaft timing wheel are not the same as the camshaft timingwheel. The camshaft timing wheel includes 37 timing teeth with 36 of the teeth spaced equallyat 10° apart. One tooth is spaced 5° apart from the other teeth.

There are only 35 teeth on the crankshaft gear spaced equally at 10° apart. Two of the teeth arespaced at 20° apart, which creates a "gap" in the gear teeth.

When the Engine ECM uses the cam speed sensor to determine timing for engine starting, theECM knows exactly what cylinder is at TDC. The following cylinders are at TDC at the sametime (one cylinder bank only):

- Cylinder No. 1 (compression stroke) and No. 6 (exhaust stroke)



When the Engine ECM uses the crank speed sensor to determine timing for engine starting, theECM does not know which of the two cylinders is at TDC. As an example, the Engine ECMwill attempt to fire cylinder No. 1 and check if there is any increase in the engine RPM. Ifthere is no increase in rpm, the ECM determines that the TDC timing position at that firingmoment is cylinder No. 6. This action may result in a longer engine start time.


Located behind the right pedal, the throttle position sensor (arrow) provides the desired throttleposition to the Engine ECM. If the Engine ECM detects a fault in the throttle position sensor,the throttle back-up switch in the cab can be used to increase the engine speed to 1300 rpm.

The throttle position sensor receives a regulated 8.0 ± 0.5 Volts from the Engine ECM. Thethrottle position sensor output signal is a Pulse Width Modulated (PWM) signal that varies withthrottle position and is expressed as a percentage between 0 and 100%.

To check the output signal of the throttle position sensor, connect a multimeter between Pins Band C of the throttle position sensor connector. Set the meter to read "Duty Cycle." The dutycycle output of the throttle position sensor should be:

- Low Idle: 16 ± 6%

- High Idle: 85 ± 4%

84


The pre-lubrication (QuickEvac) pump (1) is located on the end of the secondary steering/brakerelease pump and motor assembly (2). The pump and motor assembly is now located on thefront of the front frame crossmember.

The engine oil pre-lubrication QuickEvac pump is controlled by the Transmission/ChassisECM. The Transmission/Chassis ECM energizes the pre-lubrication pump relay located behindthe cab. The relay behind the cab then energizes the prelube relay on the left frame.

The QuickEvac mode is used to allow the technician to quickly evacuate the oil for an oilchange. The QuickEvac mode can only be performed when the engine lockout is activated.

Engine starting and pre-lubrication functions are also inhibited when the engine lockout isactivated.

85


12

If the truck is equipped with an ether start system, the Engine ECM will automatically injectether from the ether valve (arrow) and ether cylinder during cranking. The amount of automaticether injection depends on the engine oil or jacket water coolant temperature. The Engine ECMsends a duty cycle signal to the ether injection relay. The maximum duty cycle is 50%. A 50%duty cycle will pulse the ether relay ON three seconds and OFF three seconds. The maximumether delivery is ten 3-second shots per minute. Each shot delivers 6 ml (0.2 oz) of ether.

The Engine ECM will energize the ether injection relay only if:

- Engine intake manifold air temperature is below a certain temperature.- Engine coolant temperature is below a certain temperature.

Cat ET can be connected to the machine to turn the ether injection system ON or OFF.

86


87

Engine Derates

The coolant temperature sensor measures the temperature of the coolant.

When the temperature of the coolant exceeds 110° C (230° F), the Engine ECM will initiate aLevel 1 Warning.

When the temperature of the coolant exceeds 111° C (231° F), the Engine ECM will initiate aLevel 2 Warning. At 111° C (231° F) the Engine ECM will initiate a 25% derate. Refer to theillustration for the remainder of the high engine coolant temperature derates. At 100% derate,the engine available power will be approximately 50%.


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The intake manifold air temperature sensor measures the temperature of the air that is flowingto the intake manifold. The sensor is used to initiate warning levels and engine derates.

After the engine is running for at least 3 minutes and if the intake manifold air temperature goesabove 82° C (180° F), the Engine ECM will initiate a Level 1 Warning.

After the engine is running for at least 3 minutes and if the intake manifold air temperature goesabove 86° C (187° F), the Engine ECM will initiate a Level 2 Warning. With the Level 2Warning, the Engine ECM signals the engine to initiate a 3% derate. This derate will have a20% upper limit.


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This illustration shows a graph with the two different warning levels for low oil pressure andthe low oil pressure derate.

When the oil pressure is below the blue line (154 kPa @ 1600 rpm) (22 psi @ 1600 rpm), theEngine ECM will enable the low oil pressure Level 1 Warning. Change machine operation orperform maintenance to the system in the event of a warning.

When the oil pressure is below the red line (104 kPa @ 1600 rpm) (15 psi @ 1600 rpm), theEngine ECM will enable the low oil pressure Level 3 Warning. The operator shouldimmediately perform a safe engine shutdown in the event of a Level 3 Warning.

Also, with the Level 3 Warning the Engine ECM initiates a 35% engine derate.

If the signal between the Engine ECM and the oil pressure sensor is lost or disabled, the EngineECM will initiate a low engine oil pressure Level 1 Warning.


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The air inlet restriction is the pressure difference between the turbo inlet pressure sensor and theatmospheric sensor. The turbo inlet pressure sensor measures the air inlet pressure at theturbocharger compressor housing.

As the air restriction increases, the pressure difference will increase. If the engine has beenrunning for over 4 minutes and the air inlet restriction is 7.5 kPa (30 in. of water) for 30seconds, the Engine ECM will initiate a Level 1 Warning. If the air restriction increases to 9.0 kPa (36 in. of water) for 30 seconds or the turbo inlet pressure sensor fails, then a Level 2Warning will occur and the engine will enter the air inlet restriction derate.

When the pressure difference between the turbo inlet pressure sensor and the atmosphericsensor reach a difference of 10.0 kPa (40 in. of water), the Engine ECM will derate the engineapproximately 2%. The Engine ECM will then derate the engine 2% more for every 1 kPadifference up to 20%.


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This illustration shows the graph for the warning and the derates map for the fuel temperature.When the fuel temperature exceeds 90° C (194° F), the Engine ECM will activate a Level 1Warning. When the fuel temperature increases to 91.0° C (196° F) a Level 2 Warning will beinitiated by the Engine ECM. At the same time, the engine will derate to 12.5%. If the fueltemperature exceeds 92° C (198° F), the engine will be derated to 25%.

A fuel temperature sensor open circuit will derate the engine to 12.5%.

Excessive fuel temperature will cause injector wear.


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When the differential pressure switch recognizes a fuel pressure of 138 kPa (20 psi) for 1 hour,the Engine ECM will initiate a Level 1 Warning.

When the differential pressure switch recognizes 138 kPa (20 psi) across the filter for 4 hours,the Engine ECM will initiate a Level 2 Warning. With the Level 2 Warning initiated, a 35 %derate is applied to the engine.

This feature will be disabled when the fuel temperature is below 30° C (86° F).


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Engine Compression Brake

The 773F/775F Trucks can be equipped with the optional engine compression brake. Thecompression brake provides higher downhill travel speeds and reduces brake wear in additionto the Automatic Retarder Control (ARC) system. The compression brake uses a master/slavehydraulic actuation system to open exhaust valves on the compression stroke which releasespressurized air and creates a net braking force at the flywheel.

The compression brake assembly, as shown in this illustration, controls two cylinders. Thecompression brake assembly is mounted to the rocker arm shaft supports below the enginevalve covers. The compression brake is pressurized with engine oil from the rocker arm shaftand uses a solenoid valve to control oil flow in the brake housing.

The compression brake is activated by a signal from the Engine ECM to the solenoid valve (1).As the fuel injector rocker arm pushes up on the master piston (2), the corresponding slavepiston (3) is pressurized to push down on the exhaust valve bridge, decompressing the cylinderand preventing the normal power stroke.

On the C27 engine, up to six brake assemblies are used. The control circuit for thecompression brake permits the operation of either two, four, or all six of the compression brakeassemblies which provides progressive braking capabilities with the retarding effect of four,eight, or all 12 of the engine cylinders.

Compression brake system service consists of only periodic valve lash checks.

93


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This illustration shows the oil flow in the C27 engine compression brake. Oil from the engineoil pump flows through the rocker arm shaft oil passage. The compression brake solenoidvalve controls the oil flow in the compression brake hydraulic circuit.

When the Engine ECM energizes the solenoid, oil flows through the check valves to the slavepistons and the master pistons.

Oil pressure overcomes spring force and the master piston moves down and contacts the fuelinjector rocker arm. The master piston will follow the movement of the fuel injector rockerarm. As the fuel injector rocker arm moves up the master piston moves up and causes the oil toclose the check valve.

With the check valve closed, oil pressure increases in the compression brake hydraulic circuitand the slave piston is forced down. The slave piston makes contact with the exhaust valverocker arm and causes the exhaust valve to open. As the exhaust valve opens, the enginecylinder pressure is relieved through the open exhaust valve, which creates a net braking forceat the flywheel.


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When the fuel injector rocker arm moves down, the master piston moves down and thehydraulic pressure decreases. The exhaust valves are returned to the closed position by theexhaust rocker arm. The check valve opens and relieves the oil pressure.

When the Engine ECM de-energizes the compression brake solenoid, oil is drained from theslave and master pistons to the tank. The exhaust valves close and the slave piston returns tothe starting position.


95

This illustration shows the wiring and components of the engine compression brake.

When the compression brake switch in the cab is activated, the Brake ECM sends a signal tothe Engine ECM via the Cat Data Link. The Engine ECM controls the compression brakesolenoids to slow the machine.

The Engine ECM provides three levels of braking: LOW, MEDIUM, and HIGH.

When the ECM commands a LOW braking level, two solenoids (one on each valve bank) willactivate the compression brake for four cylinders (5, 7, 6, and 8).

When the ECM commands a MEDIUM braking level, four solenoids (two on each valve bank)will activate the compression brake for eight cylinders (5, 7, 6, 8, 9, 11, 2, and 4).

When the ECM commands a HIGH braking level, six solenoids (three on each valve bank) willactivate the compression brake for all 12 cylinders.


Cat Data Link +Cat Data Link -Compression Brake EnableSensor Return

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Cat Data Link -Cat Data Link +

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Compression Brake Med / HiCompression Brake Low / Hi

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Solenoid1 and 3

CompressionBrake

Solenoid6 and 8

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Solenoid2 and 4

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Solenoid10 and 12

Left Bank Valve CoverEntry Connector

Right Bank Valve CoverEntry Connector

Engine ECM

Brake ECM

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Compression BrakeEnable Switch

ENGINE COMPRESSION BRAKE SCHEMATIC

96

This chart shows an example of the ARC and engine compression brake levels in a one minuteperiod during a drive cycle.

When the machine speed exceeds a pre-determined speed, the ARC system is activated to slowthe machine. If further braking is required, the Engine ECM will command the enginecompression brake to the LOW, MEDIUM, or HIGH brake level setting as necessary to slowthe machine.


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Cooling System

The jacket water cooling system on the 773F/775F uses a Next Generation Modular Radiator(NGMR). The NGMR (arrow) is a single-pass flow design, replacing the two-pass flow foldedcore system. The coolant enters at the top left and flows out at the bottom right, similar to anautomotive design. Being modular, individual cores may be removed for service while theradiator remains in place.

97


ThermostatHousing

Radiator

Water Pump

Engine Oil Cooler

BrakeOil Cooler

Transmission andTorque Converter

Oil Cooler

Engine Block

ATAAC

COOLING SYSTEM FLOW

Jacket water coolant flows from the water pump (1) through the engine oil cooler (2), throughthe brake oil cooler (3), and the transmission and torque converter oil cooler (4) to both sides ofthe engine cylinder block. Coolant flows through the engine block to the cylinder heads. Fromthe cylinder heads, the coolant flows to the two temperature regulators and, based on coolanttemperature, either flows to the radiator (if hot) or through the bypass tube (5) to the waterpump (if cold) to recirculate until the engine reaches operating temperature.

The thermostats are located in the thermostat housing (6) at the top of the bypass tube.

The bottom illustration shows a schematic of the coolant flow.

98

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Lubrication System

The engine oil pump draws oil from the oil pan through a screen.

Oil flows from the pump through an engine oil cooler bypass valve to the engine oil cooler.The bypass valve for the engine oil cooler permits oil flow to the system during cold startswhen the oil is thick or if the cooler is plugged.

Oil flows from the engine oil cooler to the oil filters. The oil flows through the filters andenters the engine cylinder block to clean, cool, and lubricate the internal components and theturbochargers.


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Fuel System

The fuel tank is located on the left side of the truck. Fuel is pulled from the tank through theprimary fuel filter by the fuel transfer pump.

Priming is now done electrically using a switch (arrow) located above the primary fuel filter. Areusable fuel/water separator mounts directly to the bottom of the fuel filter.

101


The fuel transfer pump (arrow) is located at the top rear of the engine. The fuel transfer pumpcontains a bypass valve to protect the fuel system components from excessive pressure. Thebypass valve setting is higher than the setting of the fuel pressure regulator. Fuel flows fromthe transfer pump to the secondary fuel filter located on the right side of the engine.

102


The differential fuel pressure switch (1) is located in the top of the secondary fuel filter housingon the right side of the engine. This switch will indicate a restriction in the fuel filter. Awarning will be sent by the Engine ECM to the monitoring system.

The fuel pressure sensor (2) is located in the top of the secondary fuel filter housing, directlybehind the differential pressure switch. This sensor is used to monitor fuel pressure.

The engine fuel temperature sensor (3) is located in the top of the secondary fuel filter housing,behind the other two sensors. The Engine ECM uses the fuel temperature measurement tomake corrections to the fuel rate and maintain power regardless of fuel temperature (withincertain parameters). This feature is called "Fuel Temperature Compensation."

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Fuel flows from the secondary fuel filter base through the hoses (1) to the MEUI fuel injectors.Return fuel from the injectors flows through the fuel pressure regulator (2) before returning tothe fuel tank. Fuel pressure is controlled by the fuel pressure regulator.

Fuel pressure should be between 420 and 840 kPa (61 and 122 psi) at Full Load rpm.

104


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105

The 773F/775F now has a fuel cooler (arrow). The fuel cooler is located in front of the radiatorand below the aftercooler core. Fuel flows from the fuel regulator, through the fuel cooler, andto the tank.


106

Fuel is pulled from the tank through the primary fuel filter by the fuel transfer pump. Fuelflows from the transfer pump to the secondary fuel filter.

Fuel flows from the secondary fuel filter base through the fuel injectors in the cylinder heads.Return fuel from the injectors flows through the fuel pressure regulator and fuel cooler beforereturning to the tank.

The electric fuel priming pump is used to fill the filters after they are changed.


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When an injector is replaced, the injector trim codes must be retrieved and installed in theEngine ECM. The trim code files are located on a CD that comes with the new injector or canbe obtained from the Service Information System (SIS).

Access the trim code files from the Cat ET Service menu as shown in the illustration.


108

Select the injector trim file from either the CD or from the appropriate directory on thecomputer if the trim file was obtained from SIS.


Air Intake and Exhaust System

Shown are the air intake system components. Check the air filter restriction indicators (1). Ifthe yellow piston is in the red zone, the air filters are restricted and must be serviced.

When servicing the filter elements, clean the precleaners (2) and dust valves (3) using air orwater pressure, or detergent wash.

The dust valve is OPEN when the engine is OFF and closes when the engine is running. Thedust valve must be flexible and closed when the engine is running or the precleaner will notfunction properly and the air filters will have a shortened life.

Two filter elements are installed in the filter housings. The large element is the primaryelement and the small element is the secondary element.

Air intake system tips:

- The primary element can be cleaned a maximum of six times.

- Never clean the secondary element for reuse. Always replace the secondary element.

- Air filter restriction causes black exhaust smoke and low power.

109


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There is a turbocharger inlet pressure sensor (1) located in the tube between the air filters andthe turbochargers. This illustration shows the inlet pressure sensor from above, looking behindthe fresh air inlets (2) above the air filter canisters. The Engine ECM uses the turbochargerinlet pressure sensor in combination with the atmospheric pressure sensor to determine air filterrestriction. The ECM provides the input signal to the monitoring system, which informs theoperator of the air filter restriction.

As the air restriction increases, the pressure difference will increase. If the engine has beenrunning for over 4 minutes and the air inlet restriction is 7.5 kPa (30 in. of water) for 30seconds, the Engine ECM will initiate a Level 1 Warning. If the air restriction increases to 9.0kPa (36 in. of water) for 30 seconds or the turbo inlet pressure sensor fails, then a Level 2Warning will occur and the engine will enter the air inlet restriction derate.

When the pressure difference between the turbo inlet pressure sensor and the atmosphericsensor reach a difference of 10.0 kPa (40 in. of water), the Engine ECM will derate the engineapproximately 2%. The Engine ECM will then derate the engine 2% more for every 1 kPadifference up to 20%.

110


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The C27 engine is equipped with two turbochargers, one on each side. Each turbocharger isdriven by the exhaust gas from the cylinders which enters the turbine side (1) of theturbocharger from the exhaust manifold. The exhaust gas flows through the turbocharger,spinning the turbine wheel, then exits to the exhaust piping and muffler.

The clean air from the filters enters the compressor side (2) of the turbocharger where it iscompressed by the spinning turbine and picks up heat. The compressed air from theturbocharger then flows out the top of the turbocharger to the aftercooler. After the air is cooledby the aftercooler, the air flows to the cylinders and combines with the fuel for combustion.

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The compressed air that was heated at the turbochargers is routed through a finned Air to AirAftercooler (ATAAC) core (arrow) mounted in front of the radiator. Outside air passes throughthe ATAAC core and the radiator to cool both the intake air and the engine coolant. Thecooled, compressed air exits the aftercoolers and is piped to the intake manifolds.

112


Shown is the turbocharger outlet pressure sensor (1). The turbocharger outlet pressure sensorsends an input signal to the Engine ECM. The Engine ECM compares the value of the turbooutlet pressure sensor with the value of the atmospheric pressure sensor (2) and calculates boostpressure.

The best way to check for a power problem is to compare the truck performance with therimpull charts in the Caterpillar Performance Handbook or the individual specalogs for the773F or 775F. The truck should be able to climb a grade in the same gear as specified in thesetwo publications.

If an engine power problem is suspected, check boost pressure at full load rpm. If boostpressure is correct at full load rpm, the engine is not the problem and other systems such as thetorque converter should be checked.

To check boost pressure at full load rpm, the truck must be operated in FIRST GEAR with thethrottle at MAXIMUM and the retarder gradually engaged. Traveling up a grade is best as longas the engine rpm does not fall below the full load rpm specification during the test. Graduallyengage the retarder until the full load rpm is displayed. When the full load rpm is displayed,record the boost pressure. If boost pressure is within the specifications at full load rpm, theengine is operating correctly.

NOTE: The monitoring system includes a transmission stall test that can be used tocheck boost at full load. Cat ET should be used to view the status while running thetransmission stall test.

113


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Use Cat ET or the monitoring system display panel to view the engine rpm and boost pressure.

Generally, Torque Converter (TC) stall speed (in gear, full throttle, zero ground speed) is usedto determine if the engine power is low or a torque converter problem exists. For example, ifthe engine power is within specification and the stall speed is high, the torque converter mayhave a problem (low internal oil pressure, poor internal tolerances or damaged components).

NOTE: The 775F has a torque limiting function and engine speed is always limited to1831 rpm during the stall test.


The exhaust system (arrow) has been redesigned on the 773F/775F. The exhaust system exitson the right side of the machine and no longer runs through the frame.

114


115

This schematic shows the flow through the air induction and exhaust system.

The turbochargers are driven by the exhaust gas from the cylinders which enters the turbineside of the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping,and the mufflers.

The clean air from the filters enters the compressor side of the turbochargers. The compressedair from the turbochargers flows to the ATAAC. After the air is cooled by the ATAAC, the airflows to the cylinders and combines with the fuel for combustion.


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POWER TRAIN

The 773F/775F Off-highway Truck power train is electronically controlled. TheTransmission/Chassis ECM controls the ECPC transmission shifting and the torque converterlockup clutch operation. The transmission has seven forward speeds and one reverse speed.

Power flows from the engine to the rear wheels through the power train. The main power traincomponents are:

- Torque converter (1)

- Drive shaft (2)

- Transfer gears (3)

- Transmission (4)

- Differential (5)

- Final drives (6)

Other power train components visible in this illustration are the transmission charge filter (7)and the transmission oil cooler (8).


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These illustrations show the location of the main electronic components in the power train. TheTransmission/Chassis ECM (1) is located behind the cab seat and is accessed by removing apanel at the rear of the cab. The transmission modulating valves (2) are located on top of thetransmission planetary gears and are accessed by removing a cover plate. The torque converterlockup clutch solenoid valve (3) is located on the rear of the torque converter.

NOTE: The Transmission/Chassis ECM receives input signals from severalcomponents located on the machine to control transmission shifting and the torqueconverter lockup clutch operation. The electronic components will be covered later inthe presentation.

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118

Power Train Hydraulic System

Shown is the transmission and torque converter hydraulic system for the 773F/775F. A two-section pump is located at the rear of the torque converter housing. The first section (attachedto pump drive at rear of torque converter) takes oil from the bottom of the torque converter caseand sends the oil to the transmission and torque converter oil filter and then to the torqueconverter lockup clutch valve and transmission control valves. Oil flows from the torqueconverter lockup clutch valve to the torque converter lockup clutch. Oil flows from thetransmission control valves to the torque converter (TC inlet). Oil from the torque converterthen flows to the outlet relief valve and the torque converter and transmission oil cooler.

The second section scavenges oil from the transmission sump through a screen and sends oil tothe torque converter case.


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In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressure and locks the turbine tothe impeller. The housing, impeller, turbine, and output shaft then rotate as a unit at enginerpm. The stator, which is mounted on a one-way clutch, is driven by the force of the oil in thehousing. The one-way clutch permits the stator to turn freely in DIRECT DRIVE when torquemultiplication is not required.

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This sectional view shows a torque converter in CONVERTER DRIVE. The lockup clutch(yellow piston and blue discs) is not engaged. During operation, the rotating housing andimpeller (red) can rotate faster than the turbine (blue). The stator (green) remains stationaryand multiplies the torque transfer between the impeller and the turbine. The output shaft rotatesslower than the engine crankshaft, but with increased torque.

The two-section power train pump (1) is located at the bottom rear of the torque converter.

Oil flows from the charge pump to the torque converter lockup clutch (2). Oil from the chargepump also flows to the transmission to provide oil for the transmission modulating valves andthen to the torque converter. Some of the oil will leak through the torque converter to thebottom of the housing to be scavenged. Most of the oil in the torque converter is used toprovide a fluid coupling and flows through the torque converter outlet relief valve (3).

The outlet relief valve maintains the minimum pressure inside the torque converter. The mainfunction of the outlet relief valve is to keep the torque converter full of oil to prevent cavitation.The outlet relief pressure can be measured at the tap (4) on the outlet relief valve.

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From the outlet relief valve, oil flows to the torque converter and transmission oil cooler (5).The oil cooler is located on the right side of the engine.

The torque converter lockup clutch valve directs oil to engage the torque converter lockupclutch. The torque converter lockup clutch pressure can be checked at the tap (6) on top of thelockup clutch valve.

Excess oil that accumulates in the bottom of the transmission is scavenged by the first sectionof the pump through a screen behind the access cover (7) and returned to the torque convertersump.

NOTE: A torque converter outlet temperature sensor (not shown), located on thebottom of the outlet relief valve, provides an input signal to the Transmission/ChassisECM. The ECM sends a signal to the monitoring system to inform the operator of thetorque converter outlet temperature.


123

The torque converter lockup clutch modulating valve contains a proportional solenoid thatreceives a signal from the Transmission/Chassis ECM to engage and release the torqueconverter lockup clutch.

In this illustration, the lockup clutch modulating valve is shown with no current signal appliedto the solenoid (TORQUE CONVERTER DRIVE or NEUTRAL). The Transmission/ChassisECM controls the rate of oil flow through the lockup clutch modulating valve to the lockupclutch by changing the signal current strength to the solenoid. With no current signal applied tothe solenoid, the transmission modulating valve is DE-ENERGIZED and oil flow to the clutchis blocked.

Pump oil flows into the valve body around the valve spool and into a drilled passage in thecenter of the valve spool. The oil flows through the drilled passage and orifice to the left sideof the valve spool to a drain orifice. Since there is no force acting on the pin assembly to holdthe ball against the drain orifice, the oil flows through the spool and the drain orifice past theball to the tank.

The spring located on the right side of the spool in this view holds the valve spool to the left.The valve spool opens the passage between the clutch passage and the tank passage and blocksthe passage between the clutch passage and the pump supply port. Oil flow to the clutch isblocked. Oil from the clutch drains to the tank preventing clutch engagement.


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In this illustration, the modulating valve is shown with a maximum current signal commandedto the solenoid. When the modulation cycle stops, the Transmission/Chassis ECM sends themaximum specified current signal to fully engage the lockup clutch (DIRECT DRIVE).

The constant current signal pushes the pin firmly against the ball in the solenoid valve. The pinforce against the ball blocks more oil from flowing through the drain orifice. This restrictioncauses an increase in pressure on the left side of the valve spool. The valve spool moves to theright to allow pump flow to fully engage the clutch.

In a short period of time, maximum pressure is felt at both ends of the proportional solenoidvalve spool. This pressure along with the spring force on the right end of the spool cause thevalve spool to move to the left until the forces on the right end and the left end of the valvespool are balanced.

The valve spool movement to the left (balanced) position reduces the flow of oil to the engagedclutch. The Transmission/Chassis ECM sends a constant maximum specified current signal tothe solenoid to maintain the desired clutch pressure.

NOTE: The lockup clutch valve is calibrated with Cat ET.


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The filter has a bypass switch (2) which provides an input signal to the monitoring system, viathe Transmission/Chassis ECM, to inform the operator if the filter is restricted. The filterhousing includes a S•O•S tap (3) and a torque converter and transmission circuit pressure tap (4).

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The torque converter and transmission charging filter (1) is located on the left frame rail behindthe front tire. Oil from the charging pump flows through the torque converter filter andtransmission to the torque converter lockup clutch valve.

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Transmission Hydraulic System

The torque converter and transmission scavenge pump section pulls oil from the bottom of thetransmission case through a magnetic screen and sends the oil to the torque converter sump.The magnetic screen should always be checked for debris if a problem with the transmission issuspected.

The charging pump pulls oil from the torque converter sump. Charging oil flows from thepump through the transmission charging filter to the transmission main relief valve and sevenmodulating valves.

The main relief valve regulates the torque converter inlet pressure and supply pressure insidethe transmission hydraulic system. Oil unseats the check ball and forces the spool to the right ifthe transmission system pressure becomes greater than the spring force on the right of thespool. Excess oil will flow to the torque converter, lubrication circuit, and the lube relief valve.The lubrication circuit oil and oil from the lube relief valve flows to the transmission sump.The relief valve is adjustable by turning the adjusting screw on the right end of the valve.


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The clutch modulating valves control the engagement of the transmission clutches. Thesolenoids are controlled by a pulse width modulated (PWM) signal from theTransmission/Chassis ECM. Supply oil flows into the clutch modulating valves and through apassage in the center of the spool. Oil then flows to the tank if the solenoid is not energized.Oil flow is blocked by a ball and seat if the solenoid is energized. The spool will shift downand the clutch will begin to fill. The signal from the Transmission/Chassis ECM determineshow long it takes to fill each clutch.

The transmission lubrication relief valve limits the transmission lubrication oil pressure.


The ECPC transmission hydraulic controls can be accessed by removing a cover plate (1) ontop of the transmission. The transmission input speed sensor (2) is located on top of thetransfer gear housing. The transmission input speed sensor sends an input to theTransmission/Chassis ECM which checks the speed of the drive shaft to the speed of theengine.

The transmission has pressure taps located on the outside of the transmission which aids inpreventing contamination from entering the transmission as well as saving time when checkingthe pressures on the 773F/775F transmission. The transmission lubrication pressure tap (3) andthe transmission hydraulic system pressure tap (4) are located toward the rear of thetransmission. Oil pressure for the seven clutches can be checked at the remaining seven taps (5) on the transmission. Lube pressure can also be checked at the tap (6) on the left side ofthe transmission.

The torque converter and transmission breather (7) is located at the rear of the transmission.

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The transmission modulating valves control the oil to corresponding transmission clutches. Thesolenoid valves are:

- Clutch No. 1 Solenoid valve (1)- Clutch No. 2 Solenoid valve (2)- Clutch No. 3 Solenoid valve (3)- Clutch No. 4 Solenoid valve (4)- Clutch No. 5 Solenoid valve (5)- Clutch No. 6 Solenoid valve (6)- Clutch No. 7 Solenoid valve (7)

The main relief valve (8) controls the transmission hydraulic pressure, and the lubrication reliefvalve (not visible) controls the lubrication pressure. The lubrication relief valve is locatedbelow the main relief valve.

Also located on the transmission hydraulic control valve is the transmission hydraulic oiltemperature sensor (9). The temperature sensor sends a signal to the Transmission/ChassisECM indicating transmission oil temperature.


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The table in this illustration lists the solenoids that are energized and clutches that are engagedfor each transmission speed. This table can be useful for transmission diagnosis.


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In this illustration, the transmission modulating valve is shown with no current signal applied tothe solenoid. The Transmission/Chassis ECM controls the rate of oil flow through thetransmission modulating valves to the clutches by changing the signal current strength to thesolenoid. With no current signal applied to the solenoid, the transmission modulating valve isDE-ENERGIZED and oil flow to the clutch is blocked.

Pump oil flows into the valve body around the valve spool and into a drilled passage in thecenter of the valve spool. The oil flows through the drilled passage and orifice to the left sideof the valve spool to a drain orifice. Since there is no force acting on the pin assembly to holdthe ball against the drain orifice, the oil flows through the spool and the drain orifice past theball to the tank.

The spring located on the right side of the spool in this view holds the valve spool to the left.The valve spool opens the passage between the clutch passage and the tank passage and blocksthe passage between the clutch passage and the pump supply port. Oil flow to the clutch isblocked. Oil from the clutch drains to the tank preventing clutch engagement.


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In this illustration, the modulating valve is shown with a signal to the solenoid that is below themaximum current. Clutch engagement begins when the Transmission/Chassis ECM sends aninitial current signal to ENERGIZE the solenoid. The amount of commanded current signal isproportional to the desired pressure that is applied to the clutch during each stage of theengagement and disengagement cycle.

The start of clutch engagement begins when the current signal to the solenoid creates amagnetic field around the pin. The magnetic force moves the pin against the ball in proportionto the strength of the current signal from the Transmission/Chassis ECM.

The position of the ball against the orifice begins to block the drain passage of the oil flow fromthe left side of the valve spool to the tank. This partial restriction causes the pressure at the leftend of the valve spool to increase. The oil pressure moves the valve spool to the right againstthe spring. As the pressure on the right side of the valve spool overrides the force of the spring,the valve spool shifts to the right.

The valve spool movement starts to open a passage on the right end of the valve spool for pumpsupply oil to fill the clutch. Oil also begins to fill the spring chamber on the right end of thespool.


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In the initial clutch filling stage, the Transmission/Chassis ECM commands a high current pulseto quickly move the valve spool to start filling the clutch. During this short period of time, theclutch piston moves to remove the clearances between the clutch discs and plates to minimizethe amount of time required to fill the clutch. The ECM then reduces the current signal whichreduces the pressure setting of the proportional solenoid valve. The change in current signalreduces the flow of oil to the clutch. The point where the clutch plates and discs start to touchis called TOUCH-UP.

Once TOUCH-UP is obtained, the Transmission/Chassis ECM begins a controlled increase ofthe current signal to start the MODULATION cycle. The increase in the current signal causesthe ball and pin to further restrict oil through the drain orifice to tank causing a controlledmovement of the spool to the right. The spool movement allows the pressure in the clutch toincrease.

During the MODULATION cycle, the valve spool working with the variable commandedcurrent signal from the Transmission/Chassis ECM acts as a variable pressure reducing valve.

The sequence of partial engagement is called desired slippage. The desired slippage iscontrolled by the application program stored in the Transmission/Chassis ECM.


133

In this illustration, the modulating valve is shown with a maximum current signal commandedto the solenoid. When the modulation cycle stops, the Transmission/Chassis ECM sends themaximum specified current signal to fully engage the clutch.

The constant current signal pushes the pin firmly against the ball in the solenoid valve. The pinforce against the ball blocks more oil from flowing through the drain orifice. This restrictioncauses an increase in pressure on the left side of the valve spool. The valve spool moves to theright to allow pump flow to fully engage the clutch.

In a short period of time, maximum pressure is felt at both ends of the proportional solenoidvalve spool. This pressure along with the spring force on the right end of the spool cause thevalve spool to move to the left until the forces on the right end and the left end of the valvespool are balanced.

The valve spool movement to the left (balanced) position reduces the flow of oil to the engagedclutch. The Transmission/Chassis ECM sends a constant maximum specified current signal tothe solenoid to maintain the desired clutch pressure.


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The different maximum specified pressures for each clutch is caused by different maximumcurrent signals being sent by the Transmission/Chassis ECM to each individual modulatingvalve. The different maximum signal causes a difference in the force pushing the pin againstthe ball to block leakage through the drain orifice in each solenoid valve. The different rate ofleakage through the spool drain orifice provides different balance positions for the proportionalsolenoid valve spool. Changing the valve spool position changes the flow of oil to the clutchand the resulting maximum clutch pressure.

The operation of the proportional solenoid to control the engaging and releasing of clutches isnot a simple on and off cycle. The Transmission/Chassis ECM varies the strength of thecurrent signal through a programmed cycle to control movement of the valve spool.

The clutch pressures can be changed using Caterpillar Electronic Technician (ET) during thecalibration procedure.


134

The transmission hydraulic control relief valve is used to regulate the pressure to the torqueconverter and the main components in the transmission.

Oil enters the relief valve at the supply port. The pressure of the oil unseats the ball and movesthe spool toward the right. Oil flows past the spool and to the torque converter to regulatetransmission oil pressure.

The adjustment screw alters the preload on the spring to adjust the relief pressure.


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Rear Axle

Check the differential oil level by removing the magnetic inspection plug (1). The oil shouldbe level with the bottom of the fill plug opening. The magnetic inspection plug should beremoved at regular intervals and checked for metal particles. The plug (2) at the bottom of thedifferential housing is used to drain the oil.

Inspect the condition of the rear axle breather (3), located behind the rear suspension cylinder atregular intervals. The breather prevents pressure from building up in the axle housing.Excessive pressure in the axle housing can cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies. The parking brake oil pressure can be checkedat the pressure taps (4) on top of the axle.

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A differential carrier thrust pin is located behind the small cover (5). The thrust pin preventsmovement of the differential carrier during high thrust load conditions.

The back-up alarm (6) is located on top of the rear frame. When the machine is in reverse, theTransmission/Chassis ECM sends a signal to sound the back-up alarm.


Shown is the differential removed from the rear axle housing. The differential is located in therear axle housing behind the transmission. Power flows from the transmission to thedifferential. The differential divides the power to the right and left axle shafts. Torque istransmitted equally from the differential through the two axle shafts to the final drives. Thedifferential adjusts the speed of the axle shafts for vehicle cornering, therefore, the powerdelivered to the axle shafts is unequal during cornering.

The differential thrust pin contacts the differential carrier at the location shown (arrow). Whenhigh thrust loads are transmitted from the differential pinion to the differential ring gear, thecarrier tries to move away from the pinion. The thrust pin prevents movement of thedifferential carrier during high thrust load conditions.

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138

Transmission/Chassis Electronic Control System

Shown in this illustration are the transmission/chassis electronic control system inputs andoutputs for the 773F/775F Trucks.

The main purpose of the Transmission/Chassis ECM is to determine the desired transmissiongear and to energize the appropriate solenoids to shift the transmission up or down as requiredbased on information from both the operator and machine. The Transmission/Chassis ECMalso controls all the hoist functions, the steering disable function, and other functions asdescribed in this presentation.

The Transmission/Chassis ECM receives information from various input components such asthe shift lever switch and the transmission output speed sensors.

Based on the input information, the Transmission/Chassis ECM determines whether thetransmission should upshift, downshift, engage the lockup clutch, or limit the transmission gear.These actions are accomplished by sending signals to various output components.


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Power train output components include the transmission modulating valve solenoids and thelockup clutch solenoid. Several other Transmission/Chassis ECM output components arecovered throughout the presentation.

The Engine ECM, the monitoring system, the Transmission/Chassis ECM, and the Brake ECMall communicate with each other through the CAT Data Link. Communication between theelectronic control modules allows the sensors of each system to be shared. Many additionalbenefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when theTransmission/Chassis ECM tells the Engine ECM to reduce or increase engine fuel during ashift to lower stress to the power train.

The Electronic Technician (ET) Service Tool can be used to perform several diagnostic andprogramming functions.

NOTE: Some of the Transmission/Chassis ECM input and output components areshown during the discussion of other systems.


The Transmission/Chassis ECM (arrow) is located in the compartment at the rear of the cab.The Transmission/Chassis ECM performs the transmission control functions, plus some othermachine functions (hoist and secondary steering control). Because of the functionality of thecontrol, it is referred to as the Transmission/Chassis ECM.

The Transmission/Chassis ECM is an A4M1 module with two 70-pin connectors. TheTransmission/Chassis ECM communicates with the Engine ECM, the Brake ECM, and themonitoring system over the CAT Data Link and can communicate with some attachments overthe CAN Datalink.

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At the base of the shift lever (1) is a position sensor (2) which provides input signals to theTransmission/Chassis ECM when the operator moves the lever. The shift lever position sensoris a Hall-effect position sensor. The shift lever is connected to a device which contains twomagnets. One magnet (3) is visible in the bottom left view.

As the lever is moved, the magnets pass over the Hall Cell (4) and the change in the magneticfield produces a signal. The internal electronics (5) of the sensor process the signal and send aPWM signal to the ECM.

The lever position sensor receives 24 VDC from the machine electrical system. The sensorcontains a fourth pin that is used for calibration on some machine applications.

The following measurements would be typical for the position sensor with the sensor connectedto the Transmission/Chassis ECM and the key switch turned ON:

• Pin 1 to Pin 2 -- Supply Voltage

• Pin 3 to Pin 2 -- .7 - 6.9 DCV on DC volts scale

• Pin 3 to Pin 2 -- 4.5 - 5.5 KHz on the KHz scale

• Pin 3 to Pin 2 -- 5% - 95% duty cycle on the % scale

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Also shown in the top right illustration is the drive gear UP switch (6) and the drive gearDOWN switch (7). The drive gear switches are toggle switches that send a signal to theTransmission/Chassis ECM. When the drive gear UP switch is pressed, the high gear limit canbe increased up to seventh gear. When the drive gear DOWN switch is pressed, the high gearlimit can be decreased down to third gear.

The transmission shift lever lock button (8) unlocks the transmission shift lever when pressed.


The transmission output speed sensors (arrows) are located on the transfer gear housing on theinput end of the transmission behind a cover (not shown). Although the sensors are physicallylocated near the input end of the transmission, the sensors are measuring the speed of thetransmission output shaft. The sensors are two wire passive sensors. The passive speed sensoruses the passing teeth of the output shaft to provide a frequency signal. The signal from thesensor is used for automatic shifting of the transmission. The signal is also used to drive thespeedometer and as an input to other electronic controls.

The Transmission/Chassis ECM also performs a check between the two measured transmissionoutput speeds and the transmission input speed to ensure that the ECM calculates an accuratetransmission speed. This check also uses the speeds to determine the direction of motion of themachine.

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The engine speed sensor (arrow) is located at the rear of the engine on the left side of the gearhousing. The engine speed sensor sends a frequency signal to the Transmission/Chassis ECMindicating engine speed. The Transmission/Chassis ECM uses the engine speed signal input todetermine actual engine speed. The actual engine speed is one of the parameters used todetermine the proper transmission shift points.

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The body up switch (1) is located on the frame near the body pivot pin. This magnetic switchis normally open. When the body is raised, a magnet (2) mounted on the body passes theswitch and causes the switch to close. The resulting ground signal is sent to theTransmission/Chassis ECM. This signal is used to limit the top gear into which thetransmission will shift when the body is up.

The body up top gear value is programmable from FIRST to THIRD utilizing the Cat ETService Tool. The ECM comes from the factory with this value set to FIRST gear. Whendriving away from a dump site, the transmission will not shift past FIRST gear until the body isdown. If the transmission is already above the set limit gear when the body is raised, nolimiting action will take place.

The body up switch signal is also used to control the SNUB position of the hoist control valve.As the body is lowered and the magnet passes the body up switch, the Transmission/ChassisECM signals the hoist lower solenoid to move the hoist valve spool to the SNUB position. Inthe SNUB position, the body float speed is reduced to prevent the body from making hardcontact with the frame.

The body up switch input provides the following functions:

- Body up gear limiting

- Hoist snubbing

- Illuminates the backup lights

- Lights the body up dash lamp

- Signals a new load count (after 10 seconds in the RAISE position)

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A diagnostic code occurs if the Transmission/Chassis ECM does not receive a closed (ground)signal from the switch within four hours of operation time or an open signal from the switchwithin one hour of operation time. The body up switch must be adjusted properly for all of thefunctions to operate correctly.

The body position switch can be raised or lowered slightly in the bracket notches to start theSNUB feature sooner or later.

NOTE: The snub feature can also be adjusted in the Cat ET hoist configuration screenby selecting the "Hoist lower valve adjustment status".


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Besides controlling the Transmission Shifting and Torque Converter Lockup, theTransmission/Chassis ECM also controls other functions as shown above, such as ControlThrottle Shifting (CTS), Directional Shift Management, and Top Gear Limit.

There are several programmable parameters available with the Transmission/Chassis ECM.

NOTE: Refer to the Transmission/Chassis Electronic Control System Operation,Troubleshooting, Testing, and Adjusting manual (RENR8342) for more information onthe additional Transmission/Chassis ECM functions and programmable parameters.


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145

STEERING SYSTEM

The steering system on the 773F/775F is similar to the D and E Series trucks except a steeringdisable solenoid valve has been added and some of the component locations have changed.

When energized, the steering disable solenoid valve stops the oil flow coming from the steeringpump. This prevents the front wheels from turning to allow servicing to be conducted safely inthe front wheel area.

The steering system uses a load sensing, pressure compensated pump. Minimal horsepower isused by the steering system when the truck is traveling in a straight path. Steering hydraulichorsepower requirements depend on the amount of steering pressure and flow required by thesteering cylinders.

This illustration shows the following main steering components:

- Steering pump (1)- Steering disable valve (2)- Steering valve (3)- HMU (4)


- Steering cylinders (5)- Steering tank (6)- Secondary steering pump (7)

The steering system tank is located on the right platform.

Check the steering system oil level at the sight gauge (1).

The steering system oil filter (2) is located next to the steering tank below an access panel.

The steering system uses a pressure compensated piston-type pump. Case drain oil from thesteering pump returns to the hydraulic tank through a case drain filter (3) also located below theaccess panel.

Before removing the cap (4) to add oil to the steering system, depress the pressure release button (5) on the breather to release any remaining pressure from the tank.

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The steering system filter base and the case drain filter base have bypass valves that allow thesteering oil to bypass the filters if they are plugged.


The 773F/775F trucks are equipped with a load sensing, pressure compensated, piston-typepump. The steering pump operates only when the engine is running and provides the necessaryflow of oil for steering system operation. The steering pump contains a load sensing controllerwith two valves. The high pressure cutoff valve (1) functions as the primary steering systemrelief valve.

The flow compensator valve (2) is used to adjust the low pressure standby setting. When thetruck is traveling in a straight path, virtually no flow or pressure is sent to the steeringcylinders, and the pump destrokes to low pressure standby.

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When the truck is traveling in a straight path, the steering cylinders require virtually no flow orpressure. The HMU provides a very low pressure load sensing signal to the flow compensatorin the load sensing controller.

Pump oil (at low pressure standby) flows to the swashplate piston and past the lower end of thedisplaced flow compensator spool to the actuator piston. The actuator piston has a largersurface area than the swashplate piston. The oil pressure at the actuator piston overcomes thespring force and the oil pressure in the swashplate piston and moves the swashplate to destrokethe pump. The pump is then at minimum flow, low pressure standby.

Pump output pressure is equal to the setting of the flow compensator plus the pressure requiredto compensate for system leakage.


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During a turn, when steering pressure and flow are required, pressure increases in the HMUload sensing signal line. The pressure in the signal line is equal to the pressure in the steeringcylinders. The pump load sensing controller is spring biased to vent the actuator pistonpressure to drain. Venting pressure from the load sensing controller and the actuator pistonpositions the spring biased swashplate to maximum displacement (maximum flow).

As pressure increases in the HMU load sensing signal line, pump supply pressure is sensed onboth ends of the flow compensator. When pressure is present on both ends of the flowcompensator, the swashplate is kept at maximum angle by the force of the spring in the pumphousing and pump discharge pressure on the swashplate piston. The pistons reciprocate in andout of the barrel and maximum flow is provided through the outlet port. Since the pump isdriven by the engine, engine rpm also affects pump output.


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The steering disable valve (1) is located behind the shock on the right frame rail.

When the steering disable solenoid valve (2) is energized, oil flow from the steering pump tothe steering valve is blocked by the steering disable valve, which allows servicing behind thefront wheels with the machine running.

When the machine lockout switch, located under a panel on the left stairway, is toggled, asignal is sent to the Transmission/Chassis ECM. The Transmission/Chassis ECM energizes thesteering disable solenoid allowing service to be performed behind the front wheels safely.

Also located on the steering disable valve is a pressure tap for checking the load sensing signalto the pump, and an S•O•S tap. The taps (not visible) are located on the front of the steeringdisable valve.

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Steering oil flows from the pump through the steering disable valve to the steering valve (1)located on the frame behind the right front suspension cylinder. The primary steering pressureswitch (2) monitors the output of the steering pump. The steering pressure switch providesinput signals to the Transmission/Chassis ECM which sends a signal to the monitoring systemto inform the operator of the steering system condition. A steering system warning is displayedif the pressure is too low.

The steering pressure switch cannot tolerate high steering system pressures. A pressurereducing valve (3) reduces the steering system pressure to the steering pressure switch.

Two relief valves are located on the left side of the steering valve. The top relief valve (4) is aback-up relief valve for the secondary steering system. The secondary steering back-up reliefvalve protects the secondary steering system if the relief valve on the secondary steering pumpmalfunctions.

The lower relief valve (5) is a back-up relief valve for the primary steering system. Theprimary steering back-up relief valve protects the primary steering system if the high pressurecut-off valve on the steering pump malfunctions. Primary steering pressure is first controlledby the high pressure cutoff valve located on the steering pump.

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Check valves are used to separate the primary and secondary steering systems. The secondarycheck valve (6) is behind the left plug, and the primary check valve (7) is behind the right plug.

Steering system pressures can be measured at the steering system pressure tap (8).


This illustration shows the location of the HMU (arrow) for the 773F/775F. Serviceability hasimproved for the HMU on the 773F/775F due to the redesigned walkways. The HMU isconnected to the steering wheel and controlled by the operator.

The HMU meters the amount of oil sent to the steering cylinders by the speed at which thesteering wheel is turned. The faster the HMU is turned, the higher the flow sent to the steeringcylinders, and the faster the wheels will change direction.

The steering system is referred to as "Q-amp" which means flow amplification. During asudden steering change (steering wheel speed greater than 10 rpm), additional steering pump oilflow will bypass the gerotor pump in the HMU and flow directly to the steering cylinders.Steering oil flow to the cylinders is equal to the gerotor pump oil flow plus the bypass oil flowfrom the steering pump. The steering oil flow is amplified up to 1.6 to 1. The purpose of theflow amplification is to provide quick steering response when sudden steering changes areneeded.

Two crossover relief valves are installed in the top of the HMU. The crossover relief valves areinstalled in series with the left and right turn ports. If an outside force is applied to the frontwheels while the steering wheel is stationary, the crossover relief valves provide circuitprotection for the steering lines between the steering cylinders and the HMU. The crossoverrelief valves allow oil to transfer from one end of the steering cylinders to the opposite end ofthe cylinders.

155


To test the right crossover relief valve, install two tees with pressure taps in the right turnsteering hose at the steering cylinders. Steer the truck completely to the right against the stops,and shut off the engine. An external pump supply must be connected to one of the pressuretaps on the right turn hose. Connect a pressure gauge to the other pressure tap on the right turnhose. Pressurize the steering system, and the reading on the gauge will be the setting of theright crossover relief valve.

To test the left crossover relief valve, install two tees with pressure taps in the left turn steeringhose at the steering cylinders. Steer the truck completely to the left against the stops, and shutoff the engine. An external pump supply must be connected to one of the pressure taps on theleft turn hose. Connect a pressure gauge to the other pressure tap on the left turn hose.Pressurize the steering system, and the reading on the gauge will be the setting of the leftcrossover relief valve.


The electric secondary steering pump (1) and motor (2) on the 773F/775F are the same as the773D/775D, however the location has changed. The pump and motor are now located on thefront of the front frame crossmember. The pump and motor assembly also includes the brakerelease pump section (3) and the prelubrication (QuickEvac) pump section (4).

The secondary pressure switch (not visible) is also mounted next to the secondary steeringpump. The pressure switch detects if the wheels are being turned via the steering wheel whensecondary steering is activated. When the wheel is turned in a secondary steering condition,the pressure switch will signal the Transmission/Chassis ECM.

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If the primary steering pressure switch signals the Transmission/Chassis ECM that the steeringsystem pressure is low, the ECM will energize the secondary steering relay located behind thecab. The secondary steering relay will then energize a second larger relay located on the leftframe, which will then energize the secondary steering motor.

The primary relief valve for the secondary steering is accessible through the small allen headplug (5). To check the setting of the secondary steering primary relief valve, do not start thetruck. Turn ON the key start switch and depress the secondary steering switch in the cab. Turnthe steering wheel hard to the left or right while the secondary steering pump is running.Secondary steering system pressures can be measured at the steering system pressure tap.


158

Shown is a schematic of the steering hydraulic system in the HOLD position. The primarysteering pump pulls oil from the steering tank. All piston-type pumps produce a small amountof leakage to the case drain circuit for lubrication and cooling. The case drain oil flows to thesteering tank through a case drain filter.

Steering oil flows from the pump to the steering disable valve. When the steering disable valveis energized, oil is allowed to flow to the steering valve.

In the steering valve, a steering pressure switch monitors the output of the steering pump. Thesteering pressure switch cannot tolerate high steering system pressures. A pressure reducingvalve lowers the steering system pressure to the steering pressure switch.

If the steering pressure switch signals the Transmission/Chassis ECM that the steering systempressure is low, the ECM will then energize the secondary steering motor. Secondary steeringsupply oil will flow to the steering valve.


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Two relief valves are installed in the steering valve. The secondary steering back-up reliefvalve protects the secondary steering system if the relief valve on the secondary steering pumpmalfunctions. The primary steering back-up relief valve protects the primary steering system ifthe high pressure cut-off valve on the steering pump malfunctions.

Two check valves are located on the steering valve. The check valves are used to separate theprimary and secondary steering systems.

Steering supply oil flows to the HMU from the steering valve. Return oil from the HMU flowsthrough the steering valve and the steering filter to the steering tank.

The HMU meters the amount of oil sent to the steering cylinders by the speed at which thesteering wheel is turned. The faster the HMU is turned, the higher the flow sent to the steeringcylinders, and the faster the wheels will change direction.

Two crossover relief valves are installed in the top of the HMU. The crossover relief valves areinstalled in series with the left and right turn ports. If an outside force is applied to the frontwheels while the steering wheel is stationary, the crossover relief valves provide circuitprotection for the steering lines between the steering cylinders and the HMU. The crossoverrelief valves allow oil to transfer from one end of the steering cylinders to the opposite end ofthe cylinders.

When the Transmission/Chassis ECM energizes the secondary steering motor, load sensingsignal oil will flow from the secondary steering load sensing valve through the load sensingresolver to the HMU. The load sensing valve uses the load sensing signal pressure to controlthe amount of flow from the secondary steering pump to the steering valve.

The 773F/775F Trucks use a dynamic load sensing steering system the same as the late model "D Series" Trucks. In a dynamic system, there is load sensing pressure and flow between theHMU and the steering pumps.

A load sensing pilot signal resolver valve is located in the steering disable valve. The resolvervalve allows load sensing signal oil to flow between the HMU and the primary steering pumpor the secondary steering pump. In the NO STEER position, oil flows to the HMU. In a LEFTor RIGHT STEER position, oil also flows from the HMU to the resolver valve.

Normally, the secondary steering pump is OFF and the resolver is closed from the HMU to thesecondary steering pump. The flow from the primary steering pump holds the resolver openand load sensing pilot signal pressure is present between the HMU and the piston pump flowcompensator.

The load sensing signal flow from the primary steering pump is also used for "thermal bleed"through the HMU. The "thermal bleed" is used to keep the HMU temperature the same as therest of the steering system. Keeping the HMU the same temperature prevents sticking.


159

HOIST SYSTEM

The hoist system on the 773F/775F Update trucks is electronically controlled by theTransmission/Chassis ECM. The hoist control system operates similar to the 773D/775Dtrucks.

The main components in the hoist system are:

- Hoist control lever and position sensor (in cab)

- Hoist pump (1)

- Hoist control valve (2)

- Hoist cylinders (3)

- Hydraulic oil tank (4)


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The operator controls the hoist lever (arrow). The four positions of the hoist lever are RAISE,HOLD, FLOAT, and LOWER. The hoist valve has a fifth position referred to as the SNUBposition. The operator is unaware of the SNUB position because a corresponding lever positionis not provided. When the body is being lowered, just before the body contacts the frame, theTransmission/Chassis ECM signals the hoist lower solenoid to move the hoist valve spool to theSNUB position. In the SNUB position, the body float speed is reduced to prevent the bodyfrom making hard contact with the frame.

The hoist system can be enabled or disabled using ET. All trucks shipped from the factorywithout bodies installed are set at the DISABLED mode. The DISABLED mode is a test modeonly and will prevent the hoist cylinders from accidentally being activated. After the body isinstalled, change the hoist system to ENABLED for the hoist system to function properly.

The truck should normally be operated with the hoist lever in the FLOAT position. Travelingwith the hoist in the FLOAT position will make sure the weight of the body is on the frame andthe body pads and not on the hoist cylinders. The hoist control valve will actually be in theSNUB position.

If the transmission is in REVERSE when the body is being raised, the hoist lever sensor is usedto shift the transmission to NEUTRAL. The transmission will remain in NEUTRAL until thehoist lever is moved into the HOLD or FLOAT position and the shift lever has been cycled intoand out of NEUTRAL.

NOTE: If the truck is started with the body raised and the hoist lever in FLOAT, thelever must be moved into HOLD and then FLOAT before the body will lower.

160


The hoist lever (1) controls a position sensor (2). The PWM sensor sends duty cycle inputsignals to the Transmission/Chassis ECM. The hoist lever position sensor is a Hall-effectposition sensor and operates the same as the transmission shift lever sensor (3) previouslydescribed. Depending on the position of the sensor and the corresponding duty cycle, one ofthe two solenoids located on the hoist valve is energized.

The four positions of the hoist lever are RAISE, HOLD, FLOAT, and LOWER, but since thesensor provides a duty cycle signal that changes for all positions of the hoist lever, the operatorcan modulate the speed of the hoist cylinders.

The hoist lever sensor performs the following three functions:

- Raises and lowers the body

- Neutralizes the transmission in REVERSE

- Starts a new TPMS cycle

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Shown is the hoist and brake hydraulic tank. The oil level is checked by opening the smalldoor (1) and looking at the sight gauge. The oil level should first be checked with cold oil andthe engine stopped. The level should again be checked with warm oil and the engine running.

The lower sight gauge (2) can be used to fill the tank when the hoist cylinders are in theRAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase.After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sightgauge as explained above.

The hoist and brake tank breather is accessed by removing a cover (3) on top of the tank.Check the tank breather for restriction and clean or replace as necessary.

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Shown is the rear of the hoist and brake hydraulic tank. The hoist pump pulls oil from the tankthrough the suction screen (1) located in the rear of the tank. Brake cooling oil returns to thehydraulic tank through the upper port (2). Oil returns from the hoist valve through the port (3).

Other ports located on the hydraulic tank are:

- Makeup tank return port (4)

- Towing diverter valve return (5)

- Towing pump suction (6)

- Brake charging pump suction (7)

- Parking brake return (8)

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The hoist pump (1) is a gear-type pump that is attached to the drive gear at the rear of theengine. Mounted to the hoist pump is the brake charging pump. Oil flows from the hoist pumpto the hoist control valve.

The hoist system relief pressures are different in the RAISE and LOWER positions.

The body up switch must be in the RAISE position before the LOWER relief valve setting canbe tested. Move a magnet past the body up switch until the body up alert indicator on the dashturns ON. If the body up switch is in the LOWER position, the Transmission/Chassis ECMwill hold the hoist valve in the SNUB position and the LOWER relief valve will not open.

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In the HOLD, FLOAT, and SNUB positions, the gauge will show the brake cooling systempressure, which is a result of the restriction in the coolers, brakes, and hoses (normally muchlower than the actual oil cooler relief valve setting). The maximum pressure is limited by theoil cooler relief valve.

Hoist pump pressure can be checked at the pressure tap (2) on the pump.


The hoist control valve (1) is located behind the engine on the right side of the frame. Thehoist valve is the same as the hoist control valve on the D and E Series Trucks.

The hoist valve uses parking brake oil pressure that has been reduced by the pressure reducingvalve as the pilot oil to shift the directional spool inside the hoist valve. Oil enters thehydraulic actuators (2) on both ends of the hoist valve.

Pilot pressure can be adjusted at the pressure reducing valve (3) located next to the divertervalve (4) on the left frame rail in front of the left front strut.

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Pilot oil pressure is always present at both ends of the directional spool. Two solenoid valvesare used to drain the pilot oil from the ends of the directional spool, which then allows thespool to move. The solenoid on the right is the RAISE solenoid valve (1), and the solenoid onthe left is the LOWER solenoid valve (2).

The left pressure tap (3) is used to check the pilot pressure of the hoist lower solenoid. Theright pressure tap (4) is used to check the pilot pressure of the raise solenoid.

When the Transmission/Chassis ECM receives an input signal from the hoist lever sensor, theECM sends an output signal current between 0 and 1.9 amps to one of the solenoids. Theamount of current sent to the solenoid determines how much pilot oil is drained from the end ofthe directional spool and, therefore, how far the directional spool travels toward the solenoid.

An oil cooler relief valve is located in the hoist control valve behind the large plug (5). Therelief valve limits the brake oil cooling pressure when the hoist valve is in the HOLD, FLOAT,or SNUB position.

The hoist system relief pressures are controlled by the two relief valves located on top of thehoist valve. The RAISE relief valve (6) limits the pressure in the hoist system during RAISE.The LOWER relief valve (7) limits the pressure in the hoist system during LOWER.

NOTE: The hoist valve LOWER position (snub adjustment) is an adjustable parameterin the Transmission/Chassis ECM using Cat ET. The slight adjustment provides ameans to compensate for valve differences. This is the snub adjustment.

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The hoist cylinder lower circuit pressure tap (1) and raise circuit pressure tap (2) are located onthe cross-tube between the lower hoist cylinder mounts.

The relief valve pressure setting is tested with the engine at HIGH IDLE and the hoist valve inthe RAISE or LOWER position.

The body up switch at the frame near the body pivot pin must be in the RAISE position beforethe LOWER relief valve setting can be tested. Move a magnet past the body up switch until thebody up alert indicator on the dash turns ON. If the body up switch is in the LOWER position,the Transmission/Chassis ECM will hold the hoist valve in the SNUB position and the LOWERrelief valve will not open.

An orifice plate is installed between the upper hose and the rod end port on both hoistcylinders. The orifice plate restricts the flow of oil from the rod end of the hoist cylinders.

The orifice plate also prevents cavitation of the cylinders when the body raises faster than thepump can supply oil to the cylinders (caused by a sudden shift of the load).

NOTE: If the snub feature is not adjusted correctly, residual pressure will exist in thehead side of the cylinders and the body will not rest on the frame. The raise circuitpressure tap should be used to ensure there is no residual pressure in the head side ofthe cylinders.

Otherwise, when checking the raise (high) circuit pressure, the pressure tap on the hoist pumpis easier to access.

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This illustration shows a sectional view of the hoist control valve in the HOLD position. Pilotoil pressure is present at both ends of the directional spool. The spool is held in the centeredposition by the centering springs and the pilot oil. Passages in the directional spool vent thedual stage relief valve signal stem to the tank. All the hoist pump oil flows through the brakeoil coolers to the rear brakes.

The position of the directional spool blocks the oil in the head end and rod end of the hoistcylinders.

A gauge connected to a pressure tap at the pump while the hoist valve is in the HOLD positionwill show the brake cooling system pressure, which is a result of the restriction in the coolers,brakes, and hoses. The maximum pressure in the circuit should correspond to the setting of thebrake oil cooler relief valve.


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In the RAISE position, the raise solenoid is ENERGIZED and drains pilot oil from the upperend of the directional spool. The directional spool moves up. Pump oil flows past the loadcheck valve and the directional spool to the head end of the hoist cylinders.

When the directional spool is initially shifted, the load check valve remains closed until thesupply pressure is higher than the pressure in the hoist cylinders. The load check valveprevents the body from dropping before the RAISE pressure increases.

The directional spool also sends hoist cylinder raise pressure to the dual stage relief valvesignal stem. The dual stage relief valve signal stem moves down and blocks the supplypressure from opening the low pressure relief valve.

Oil flowing from the rod end of the hoist cylinders flows freely through the brake oil cooler tothe brakes.

If the pressure in the head end of the hoist cylinders exceeds the relief valve settings, the highpressure relief valve will open. When the high pressure relief valve opens, the dump valvemoves to the left and pump oil flows to the tank.


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The high pressure hoist relief valve setting is checked at the hoist pump pressure tap or thehead end pressure tap. Check the relief pressure with the hoist lever in the RAISE position andthe engine at HIGH IDLE.


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In the LOWER (power down) position, the LOWER solenoid is energized and drains pilot oilfrom the lower end of the directional spool. The directional spool moves down.

Supply oil from the pump flows past the load check valve and the directional spool to the rodend of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank throughholes in the directional spool. The supply oil in the rod end of the cylinders and the weight ofthe body move the cylinders to their retracted positions.

Just before the body contacts the frame, the body up switch sends a signal to theTransmission/Chassis ECM to move the directional spool to the SNUB position. In the SNUBposition, the directional spool moves slightly to restrict the flow of head end oil through onlysome of the holes in the spool which allows the body to lower gradually.

The directional spool also vents the passage to the dual stage relief valve signal stem. The dualstage relief valve signal stem allows supply pressure to be limited by the low pressure reliefvalve.

If the pressure in the rod end of the hoist cylinders is too high, the low pressure relief valve willopen. When the low pressure relief valve opens, the dump valve moves to the left and pump oilflows to the tank.


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The low pressure hoist relief valve setting is checked at the rod end pressure tap. Check therelief pressures with the hoist lever in the LOWER position and the engine at HIGH IDLE.

The body up switch must be in the RAISE position before the LOWER relief valve setting canbe tested. Move a magnet past the body up switch until the body up alert indicator on the dashturns ON. If the body up switch is in the LOWER position, the Transmission/Chassis ECMwill hold the hoist valve in the SNUB position and the LOWER relief valve will not open.


173

In the FLOAT position, the LOWER solenoid is partially energized and drains some of the pilotoil at the lower end of the directional spool to the tank. The directional spool moves down.Because the pilot oil is only partially drained, the directional spool does not move down as faras during LOWER (power down).

Pump supply oil flows past the load check valve and the directional spool to the rod end of thehoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The position of thedirectional spool permits the pressure of the oil flowing to the brake oil cooler to be felt at therod end of the hoist cylinders.

The truck should normally be operated with the hoist lever in the FLOAT position. Travelingwith the hoist in the FLOAT position will make sure the weight of the body is on the frame andbody pads and not on the hoist cylinders. The hoist valve will actually be in the SNUBposition.


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174

In the SNUB position as the body is lowered, just before the body contacts the frame, the bodyup switch sends a signal to the Transmission/Chassis ECM to move the directional spool to theSNUB position. In the SNUB position, the directional spool moves slightly to a positionbetween HOLD and FLOAT. The SNUB position restricts the flow of oil and lowers the bodygradually.

The operator does not control the SNUB position. When the hoist lever is in the LOWER orFLOAT position and the body up switch is in the DOWN position, the hoist control valve is inthe SNUB position.

A gauge connected to the rod end pressure tap while the hoist control valve is in the SNUBposition will show the brake cooling system pressure, which is a result of the restriction in thecoolers, brakes, and hoses. The maximum pressure in the circuit should correspond to thesetting of the brake oil cooler relief valve.


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175

Two-stage hoist cylinders (1) are used to raise the body. Oil flows from the hoist control valveto the two hoist cylinders when the directional spool in the hoist control valve is not in HOLD.

Check the condition of the body pads (2) for wear or damage.

Hoist pilot pressure is required to lower the body with a dead engine. The towing pump can beused to provide the hoist pilot oil.

To lower the body with a dead engine:

1. Move towing valve to TOW position

2. Turn key ON

3. Hold hoist lever in RAISE 15 seconds

4. Move hoist lever to HOLD, then FLOAT

5. Depress secondary steering switch and body will lower


1

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176

This illustration shows the hoist hydraulic system in the HOLD position. The hoist pump pullsoil from the hydraulic tank through the suction screen located in the rear of the tank. Oil flowsfrom the hoist pump to the hoist control valve.

When the hoist control valve is in the HOLD, FLOAT, or SNUB position, all the hoist pump oilflows through the brake oil cooler located on the right side of the engine. Oil flows from theoil cooler, through the rear brakes, and returns to the hydraulic tank.

A brake cooling relief valve is located in the hoist control valve. The relief valve limits thebrake oil cooling pressure when the hoist control valve is in the HOLD, FLOAT, or SNUBposition.

The hoist valve uses parking brake oil pressure that has been reduced by the pressure reducingvalve as the pilot oil to shift the directional spool inside the hoist control valve. Oil flows fromthe pressure reducing valve to both ends of the hoist control valve.


Main Relief Dump Spool

Lower,Float,Snub

Solenoid

RAISE

SNUB

FLOAT

LOWERBrake

CoolingReliefValve

RightRear

Brake

FromBrake

System

LeftRearBrake

773F / 775F HOIST AND BRAKE COOLING SCHEMATIC

HOLD

FromPressure

Reducing Valve

Orifice Plate

OrificePlate

RaiseSolenoid

DualStageSignalSpool

Raise Relief Valve

Lower Relief Valve

BrakeCooler

HoistPump

Pilot pressure is always present at both ends of the directional spool. Two solenoid valves areused to drain the pilot oil from the ends of the directional spool, which then allows thecentering springs and the pressure on the opposite end of the spool to move the spool. Whenthe RAISE solenoid is energized, the directional spool will move toward the RAISE solenoid.

The RAISE and LOWER solenoid valves constantly receive approximately 300 millivolts at afrequency of 80 Hz from the Transmission/Chassis ECM when they are in any position exceptHOLD. The excitation, referred to as "dither," is used to keep the solenoids in a ready state forquick response.

When the Transmission/Chassis ECM receives an input signal from the hoist lever sensor, theECM sends an output signal current between 0 and 1.9 amps to one of the solenoids. Theamount of current sent to the solenoid determines how much pilot oil is drained from the end ofthe directional spool and, therefore, the distance that the directional spool travels.

The truck should normally be operated with the hoist lever in the FLOAT position. Travelingwith the hoist in the FLOAT position will make sure the weight of the body is on the frame andthe body pads and not on the hoist cylinders. The hoist valve will actually be in the SNUBposition.

When the hoist control valve is in the RAISE position, pump supply oil flows to the head endof the hoist cylinders. Pump supply oil also flows to the dual stage signal spool and moves thespool to the left. When the dual stage signal spool moves to the left, pump supply oil isblocked from the LOWER relief valve, and the RAISE relief valve will limit the hoist systempressure.

When the hoist control valve is in the LOWER (power down), FLOAT, or SNUB position,pump supply oil flows to the rod end of the hoist cylinders. Pump supply oil is blocked fromthe dual stage signal spool and the spring holds the spool in the right position. When the dualstage signal spool is in the right position, pump supply oil can flow to the LOWER relief valve,and hoist system pressure is controlled by the LOWER relief valve.

An orifice plate is installed between the upper hose and the rod end port on both hoistcylinders. The orifice plate prevents cavitation of the cylinders when the body raises fasterthan the pump can supply oil to the cylinders (caused by a sudden shift of the load).


177

BRAKE SYSTEM

Two separate brake systems are used on the 773F/775F trucks. The two brake systems are theservice/retarder brake system and the parking/secondary brake system. The parking/secondarybrakes are spring engaged and hydraulically released. The service/retarder brakes arehydraulically engaged and spring released.

The braking system is also equipped with a Brake ECM that controls the braking systemfunctions, including the Automatic Retarder Control (ARC) and the Traction Control System (TCS).

The air system on the previous model trucks has been completely removed.

The main components in the braking system are:

- Brake charging pump (1)

- Accumulator charging valve (2)

- Brake accumulators (3)

- Service brake valve (4)


- Diverter (towing) valve (5)

- Brake oil filter (6)

- TCS valve (7)

6

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43

1 2

7

The rear brakes on the 773F/775F trucks are oil cooled. Shown is a cutaway illustration of anoil cooled brake assembly. The brakes are environmentally sealed and adjustment free. Oilcontinually flows through the brake discs for cooling. Duo-Cone seals prevent the cooling oilfrom leaking to the ground or transferring into the axle housing. The wheel bearing adjustmentmust be maintained to keep the Duo-Cone seals from leaking.

The smaller piston (yellow) is used to engage the secondary and parking brakes. The parkingbrakes are spring engaged and hydraulically released.

The larger piston (purple) is used to engage the service and retarder brakes. The service andretarder brakes are engaged hydraulically and released by spring force.

178


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The front brakes are a disc and caliper design. The brake caliper assemblies are fastened to thespindle and do not rotate. The brake disc is fastened to the wheel and rotates with the wheel.Air can be bled from the front brakes through the bleed valves.

During brake application, hydraulic oil from the brake cylinders forces the brake pistons againstthe brake carrier linings (brake pads). The brake linings are forced against the disc to stop therotation of the wheel.

179


The brake charging pump (1) and the hoist pump (2) are mounted to the pump drive gear on theleft rear side of the engine. The 773F/775F brake system accumulators are charged by thebrake charging pump, which supplies oil to the accumulator charging valve.

180

181


12

12

The brake system filter (1) is mounted to a bracket on the inside of the left frame rail. Thebrake filter includes a filter bypass switch (2), which sends a signal to the Brake ECM if thefilter is restricted. The Brake ECM sends a signal to the monitoring system, which illuminatesthe brake system-check indicator lamp. An S•O•S tap is located next to the brake filter.

182


2

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3

The accumulator charging valve (1) is located below the right frame rail bolted to a mountingbracket that also supports the brake accumulators. The accumulator charging valve directs oilto the brake accumulators, brake oil cooler, and the tank. Once the accumulators are charged,the excess oil flow is sent to cool the rear brakes before returning to the tank.

The Brake ECM monitors the pressure in the service brake accumulators with the brakeaccumulator pressure switch (2). If the pressure in the service brake accumulators is low, theBrake ECM will signal the monitoring system to turn on the brake system-check indicatorlamp. A relief valve (3) limits the pressure in the brake charging circuit.

183

184


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A pressure tap (4) on the line between the brake charging pump and the accumulator chargingvalve is used to check the charge oil pressure from the pump. The pressure tap (5) on thecharging valve is used to check the oil pressure in the brake accumulators.

Cut-in and cut-out pressure can be adjusted with a screw that can be accessed by removing aplug (6).


185

The accumulator charging valve maintains the pressure in the accumulators at a constant ratewhile the engine is running. If the machine has lost power or the hydraulic pump has failed, thepressure in the accumulators will permit several applications of the service brakes.

This illustration shows the accumulator charging valve in the CUT-IN position. When theaccumulator oil pressure decreases below a certain point, the accumulator charging valvereaches the cut-in pressure setting. The pressure decrease allows spring force to move the cut-in/cut-out spool to the left and oil flows to the right end of the unloading valve. The orificein the unloading valve restricts the pump flow to the brake cooling system. Oil flow to thebrake accumulators increases and the accumulators are charged.

The accumulator oil pressure switch sends a signal to the Brake ECM to alert the operator whenthe brake oil pressure drops below the minimum operating pressure.


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186

This illustration shows the accumulator charging valve in the CUT-OUT position. When theaccumulator oil pressure increases to the cut-out pressure setting, the increased pressure causesthe cut-in/cut-out spool to move right against spring force. Oil at the right end of the unloadingvalve flows to the tank. Oil pressure on the left end of the unloading spool overcomes thedecreased oil pressure on the right end of the spool and spring force. Most of the brakecharging pump oil now flows to the brake cooling system.

The check valve prevents high accumulator oil pressure from flowing to the brake coolingsystem.

The accumulator charging valve remains in the CUT-OUT position until the pressure in theaccumulators decreases to the cut-in pressure setting.

The pressure relief valve regulates the oil pressure in the brake circuit. Any excess oil that isnot required by the brake cooling system or the brake circuit is diverted back to the hydraulicoil tank.

NOTE: The pressure relief valve is set much higher than cut-out pressure and is onlyneeded as a backup if cut-out fails.


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There are two brake accumulators for the 773F/775F trucks located on the right side of thetruck. The service brake accumulator (1) and parking brake accumulator (2) are charged by thebrake charging pump and supply the required oil flow to engage the front and rear servicebrakes and to release the rear parking brakes.

A check valve in the circuit between the parking brake accumulator and the service brakeaccumulator allows only the parking brake accumulator to be charged when using the electricbrake release pump.

187


12

188


The cab brake manifold (1) is mounted below the cab on the left upper frame. The cab brakemanifold contains the ARC control solenoid (2) and the front service brake solenoid (3).

The ARC control solenoid is part of the ARC system. The ARC system uses the rear servicebrakes to automatically control the speed of the truck.

The service brake pressure switch (4) is located near the cab brake manifold toward the front ofthe machine. The service brake pressure switch sends a signal to the Brake ECM when theservice brakes are engaged. The Brake ECM will use the signal from the pressure switch toenergize the stop lamp relay (located in cab) and turn on the brake lights. In a low pressuresituation, the Brake ECM will signal the monitoring system to activate the brake system-checkindicator.

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The service brake valve (1) is mounted below the floor of the operator’s cab. When the servicebrake pedal (2) is depressed, an internal spool directs oil flow from the service brakeaccumulators to the rear service brakes.

The amount of oil flow to the front service brakes is determined by the Brake ECM based on asignal from the service brake pedal position sensor (3). The Brake ECM allows some oil fromthe brake accumulators to flow to the front brakes by controlling the position of the front brakesolenoid located in the cab brake manifold.

189

190


1

2

3

When the manual retarder lever (1) is activated, a PWM signal is sent to the Brake ECM. TheBrake ECM sends a signal to the ARC solenoid. The solenoid controls the amount of oil flowto the service brakes based on the position of the retarder lever.

If the ARC switch (2) is activated, the Brake ECM sends a signal to the ARC solenoid. Thesolenoid controls the amount of oil flow to the service brakes based upon the input signals thatthe Brake ECM receives from the engine speed sensor.

The optional engine brake switch (3) is also an input to the Brake ECM. The Brake ECMcommunicates the status of the brake switch to the Engine ECM via the Cat Data Link. TheEngine ECM controls the compression brake application (if equipped).

191


3

2

1

The rear slack adjuster (1) is located above the rear differential.

The slack adjuster compensates for brake disc wear by allowing a small volume of oil to flowthrough the slack adjuster and remain between the slack adjuster and the brake piston under lowpressure. The slack adjuster maintains a slight pressure on the brake piston at all times.

Brake cooling oil pressure maintains a small clearance between the brake discs.

The service brake oil pressure can be tested at the tap (2) located on top of the slack adjuster.

192


1

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193

This illustration shows sectional views of the slack adjuster when the brakes are RELEASEDand when the brakes are ENGAGED.

When the brakes are ENGAGED, oil from the brake cylinder enters the slack adjuster and thetwo large pistons move outward. Each large piston supplies oil to one wheel brake. The largepistons pressurize the oil to the service brake pistons and ENGAGE the brakes.

Normally, the service brakes are FULLY ENGAGED before the large pistons in the slackadjuster reach the end of their stroke. As the brake discs wear, the service brake piston willtravel farther to FULLY ENGAGE the brakes. When the service brake piston travels farther,the large piston in the slack adjuster moves farther out and contacts the end cover. The pressurein the slack adjuster increases until the small piston moves and allows makeup oil from thebrake cylinder to flow to the service brake piston.

When the brakes are RELEASED, the springs in the service brakes push the service brakepistons away from the brake discs. The oil from the service brake pistons pushes the largepistons in the slack adjuster to the center of the slack adjuster. Makeup oil that was used toENGAGE the brakes is replenished at the brake cylinder from the makeup tank.


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The spring behind the large piston causes some oil pressure to be felt on the service brakepiston when the brakes are RELEASED. Keeping some pressure on the brake piston providesrapid brake engagement with a minimum amount of brake cylinder piston travel.

The slack adjusters can be checked for correct operation by opening the service brake bleedscrew with the brakes RELEASED. A small amount of oil should flow from the bleed screwwhen the screw is opened. The small flow of oil verifies that the spring behind the large pistonin the slack adjuster is maintaining some pressure on the service brake piston.


The service brake bleed screw (1) is identified by an "S" on the brake anchor plate casting nextto the screw. The parking brake bleed screw (2) is identified by a "P" on the casting.

Another check to verify correct slack adjuster operation is to connect a gauge to the pressuretap on top of the slack adjuster and another gauge at the service brake bleed screw location onthe brake anchor plate casting.

With the service brake pedal depressed, the pressure reading on both gauges should beapproximately the same. When the brakes are RELEASED, the pressure at the slack adjustershould return to zero. The pressure at the service brake bleed screw location should return tothe residual pressure held on the brakes by the slack adjuster piston.

If the slack adjuster residual pressure is too low, it could indicate a failed slack adjuster. Highresidual pressure may indicate a failed slack adjuster or warped brake discs. To check forwarped brake discs, rotate the wheel to see if the pressure fluctuates. If the pressure fluctuateswhile rotating the wheel, the brake discs are probably warped and should be replaced.

To check for brake cooling oil leakage, block the brake cooling ports and pressurize each brakeassembly to a maximum of 138 kPa (20 psi). Close off the air supply source and observe thepressure trapped in the brake assembly for five minutes. The trapped pressure should notdecrease.

194


1

2

195


The parking brake valve (1) is located on the inside left frame rail behind the center crossmember. The parking valve receives oil flow from the parking brake accumulator. Containedwithin the valve is a parking brake solenoid valve (2) and a purge solenoid valve (3).

When the parking brake solenoid is energized by the Brake ECM, the parking brake valvedirects oil flow through the TCS valve to release the rear parking brakes. There are no parkingbrakes on the front wheels. When the transmission shift lever is moved to PARK a signal issent to the Brake ECM to engage the parking brakes. There is not a separate parking brakecontrol switch. The secondary brake pressure switch (4), located to the rear of the parkingbrake valve, sends a signal to inform the Transmission/Chassis ECM that the secondary/parkingbrake is engaged.

When the machine is shut down, the purge solenoid is energized by the Transmission/ChassisECM and the purge valve drains the brake accumulators to tank.

1

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3 4

The parking brake pressure can be checked at the left parking brake tap (1) and at the rightparking brake tap (2).

196


12

The secondary brake pedal position sensor (arrow) is located on the back of the secondarybrake pedal. The position sensor sends a signal to the Brake ECM indicating the position of thesecondary brake pedal. The Brake ECM sends a signal to the parking brake solenoid whichcontrols the secondary brake application at the rear brakes.

197


The secondary steering/brake release/QuickEvac pump and motor are located on the front of thefront frame crossmember as previously shown. The brake retract pump section (arrow)provides oil to release the parking brakes and provides hoist pilot oil for lowering the body ontrucks with a dead engine.

198


The diverter (towing) valve (1) is located on the left frame rail in front of the left front strut.The diverter valve is used to unlock the brakes for towing and must be manually shifted beforetowing.

Once the valve is shifted, oil flow from the electric secondary steering/brake retract pump isdirected to the parking brake valve to release the parking brake. The relief valve (2) limits themaximum pressure when using the brake retract pump.

To release the parking brakes for service work or towing, the electric motor on the pump isenergized by the brake release/secondary steering switch located in the cab.

199

200


3

1 2

3

1

2

When the key start switch is turned ON, the secondary steering system is energized for threeseconds to check the system. Since the towing pump is driven by the same electric motor asthe secondary steering pump, the diverter valve allows the towing pump oil to flow directly tothe hydraulic tank during the secondary steering test.

To shift the diverter valve, loosen the two diverter valve clamp bolts and slide the plate and thespool to the left. After the spool is shifted, tighten the diverter valve clamp bolts. When theelectric motor is energized, supply oil can flow from the towing pump, through the divertervalve, to the parking brake valve.

NOTE: With the engine shutoff, the purge solenoid will divert the brake release pumpsupply oil to the tank. Therefore, when towing the machine, the return lines from theparking brake valve and traction control valve must be capped to block the brakerelease pump supply oil from flowing to the tank.

The brake release pump is also used to provide pilot oil to lower the body when the engine isoff.

Located next to the diverter valve is the pressure reducing valve (3). The pressure reducingvalve reduces the parking brake system oil pressure for the hoist pilot system.


201

This schematic shows the oil flow through the hoist and brake cooling system on the773F/775F trucks. The hoist valve and the brake accumulator charging valve supply oil to thebrake cooler and the rear brakes.

The pressure in the brake cooling system is limited by the brake cooling relief valve located inthe hoist valve. The relief valve is usually needed only when the brake cooling oil is cold.When brake cooling oil is at operating temperature, the brake cooling oil pressure is usuallymuch lower than the setting of the oil cooling relief valve.


Main Relief Dump Spool

Lower,Float,Snub

Solenoid

RAISE

SNUB

FLOAT

LOWERBrake

CoolingReliefValve

RightRear

Brake

FromBrake

System

LeftRearBrake

773F / 775F HOIST AND BRAKE COOLING SCHEMATIC

HOLD

FromPressure

Reducing Valve

Orifice Plate

OrificePlate

RaiseSolenoid

DualStageSignalSpool

Raise Relief Valve

Lower Relief Valve

BrakeCooler

HoistPump

The brake oil cooler (arrow) is located on the right side of the engine. Engine coolant from thewater pump flows around the brake oil cooler and back to the cylinder block. The enginecoolant transfers the heat from the brake oil system to the engine coolant.

Oil from the brake cooling pump flows through a screen (not shown) before flowing throughthe brake oil cooler.

202


Brake cooling oil pressure can be tested at the two taps (arrows) located in the brake cooling oiltubes. One tap is located on the brake cooling inlet tube and another tap is located on the brakecooling outlet tube. The pressure measured at the brake inlet tube (from the oil coolers) willalways be higher than the pressure measured at the brake outlet tube.

A brake oil temperature sensor is located in a brake oil cooling tube on the truck. The brake oiltemperature sensor sends a signal to the Brake ECM indicating brake oil temperature. TheBrake ECM will send a signal over the Cat Data Link, which informs the monitoring system todisplay the temperature on the brake temperature gauge.

The most common cause of high brake cooling oil temperature is operating the truck in a gearrange which is too high for the grade and not maintaining a high enough engine speed. Theengine speed should be maintained at approximately 1900 rpm during long downhill hauls.

Make sure the oil cooling relief valve is not stuck open. Also, make sure the pistons in theslack adjuster are not stuck and holding too much pressure on the brakes.

203


204

This schematic shows the major components of the brake hydraulic system.

Oil is drawn from the hydraulic tank by the brake charging pump. Oil flows through the brakefilter to the accumulator charging valve. The accumulator charging valve directs supply oil tothe brake accumulators. The accumulator charging valve also controls the cut-in and cut-outpressure. When the accumulators are charged, the charging valve will direct excess pump flowto the brake cooling system.

The service brake accumulator provides oil flow to the service brake control valve. Oil alsoflows to the ARC control solenoid and front brake solenoid. When the operator depresses theservice brake pedal, the service brake control valve directs pump flow to the rear service brakesto stop the truck.

The front brakes are only engaged when the Brake ECM energizes the front brake solenoid.The Brake ECM energizes the front brake solenoid when the service brake pedal is depressed ifthe front brake switch in the cab is ON.

The Brake ECM controls the modulation of the ARC solenoid and front brake solenoid, whichcontrols truck braking when the ARC system is ON.


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Oil from the parking brake accumulator flows to the parking brake valve and the towingdiverter valve. When the parking brake is activated, the supply oil for releasing the parkingbrakes is directed to the tank and the parking brakes are engaged by spring force. When theparking brake solenoid is energized (parking brake de-activated), the parking brake valvedirects oil to the TCS valve. The pressure reducing valves in the TCS valve direct oil to releasethe parking brakes.

The diverter valve, under normal operation, is closed and blocks the oil flow from the electricbrake retract pump. If the truck is to be towed with a dead engine, the diverter valve must beshifted manually. When manually shifted, the diverter valve directs oil flow from the electricbrake retract pump to the parking brake valve to release the rear brakes.


205

Brake Electronic Control System

The 773F/775F Trucks are equipped with a Brake ECM for controlling the parking brake andfront service brake applications, the ARC system, and the TCS. The following two possibleservice brake application arrangements can be installed on a truck:

- ARC only

- ARC and TCS

The Brake ECM receives information from various input components such as the engine speedsensor, the service brake pedal position sensor, the ARC switch, and the wheel speed sensors.

Based on the input information, the Brake ECM controls the front service brake applicationwhen the service brake pedal is depressed or the rear service brake application when the ARCsystem is activated. The Brake ECM also controls when the parking brakes should engage forthe TCS and parking brake application when the parking brake is manually activated.


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Output components include the ARC solenoid, the front service brake solenoid, the TCSselector and proportional solenoids, and the parking brake solenoid.

The compression brake switch is also an input to the Brake ECM. When the compressionbrake switch is activated, the Brake ECM sends a signal over the Cat Data Link to the EngineECM. The Engine ECM controls the engine compression brake, which was covered earlier inthe presentation.


The Brake ECM (arrow) is located in the compartment at the rear of the cab. The Brake ECMperforms the brake control functions, and controls the ARC system and TCS system.

The Brake ECM is an A4M1 module with two 70-pin connectors. The Brake ECMcommunicates with the Engine ECM, Transmission/Chassis ECM, and monitoring system overthe CAT Data Link and can communicate with some attachments over the CAN Datalink.

206


207

When the service brake pedal is depressed, the service brake valve directs oil from the servicebrake accumulator to the rear brakes and sends a PWM signal to the Brake ECM via the servicebrake pedal position sensor.

The Brake ECM signals the front service brake solenoid to direct oil from the service brakeaccumulator to the front brakes if the front brake lockout switch in the cab is OFF. If thelockout switch is ON, the Brake ECM de-energizes the front service brake solenoid. Oil flowto the front brakes is blocked and only the rear brakes are used to stop the truck.

NOTE: Oil flow to the front and rear brakes may not be proportional. When the pedalis initially depressed, more oil is directed to the rear brakes. As the pedal is depressedfarther more oil is sent to the front brakes in proportion to the rear until full front brakepressure is present at full pedal travel.

The Brake ECM also de-energizes the ARC solenoid when the ARC switch in the cab is OFFand the manual retarder lever is in the NEUTRAL position.

The manual retarder lever also controls the service brake application using the ARC solenoid.


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When the retarder lever is moved, a PWM signal is sent to the Brake ECM. The Brake ECMde-energizes the front service brake solenoid. Oil flow to the front brakes is blocked and onlythe rear brakes are used to stop the truck with the retarder lever.


208

Automatic Retarder Control (ARC)

The ARC system receives signals from several switches and sensors. The main inputs to theBrake ECM for the ARC system are the ARC switch and engine speed sensor. The Brake ECManalyzes the various input signals and sends output signals to the ARC solenoid.

The ARC system function is to modulate truck braking (retarding) when descending a longgrade to maintain a constant engine speed. The ARC system engages the rear service brakes. Ifthe ARC switch is moved to the ON position, the ARC system will be activated if the throttlepedal is not depressed and the parking/secondary brakes are RELEASED. The ARC system isdisabled when the throttle is depressed or when the parking/secondary brakes are ENGAGED.

The ARC is set at the factory to maintain a constant engine speed of 2285 rpm (engine speedsetting is programmable from 2235 to 2285 rpm). When the ARC initially takes control ofretarding, the engine speed may oscillate out of the ± 50 rpm target, but the engine speedshould stabilize within a few seconds.


ARCSolenoid Service

BrakeValve

Brake ECMFrom Service

Brake Accumulator

To RearService Brakes

Front ServiceBrake Solenoid To Front

Service Brakes

ARCON / OFFSwitch

Engine SpeedSensor

Cab Manifold

AUTOMATIC RETARDER CONTROL(ARC)

For proper operation of the ARC system, the operator needs only to activate the control withthe ARC switch and select the correct gear for the grade, load, and ground conditions. TheARC system is designed to allow the transmission to upshift to the gear selected by the shiftlever. After the transmission shifts to the gear selected by the operator and the engine speedexceeds 2285 rpm, the ARC system will apply the retarder as needed to maintain a constantengine speed.

The ARC system also provides engine overspeed protection. If an unsafe engine speed isreached, the ARC will engage the brakes, even if the ARC switch is in the OFF position and thethrottle is depressed.

Trucks approaching an overspeed condition will sound a horn and activate a light. If theoperator ignores the light and horn, the ARC will engage the retarder. If the engine speedcontinues to increase, the Transmission/Chassis ECM will either upshift (one gear only aboveshift lever position) or unlock the torque converter (if the shift lever is in the top gear position).

The ARC also provides service personnel with enhanced diagnostic capabilities through the useof onboard memory, which stores possible faults, solenoid cycle counts, and other serviceinformation for retrieval at the time of service.


209

Traction Control System (TCS)

The Traction Control System (TCS) uses the rear parking/secondary brakes (spring engaged andhydraulically released) to decrease the revolutions of a spinning wheel. The TCS allows the tirewith better underfoot conditions to receive an increased amount of torque. The TCS iscontrolled by the Brake ECM and operates the same as the D and E series Trucks.

The Brake ECM monitors the drive wheels through four input signals: one at each drive axle,and two at the transmission output shaft. When a spinning drive wheel is detected, the BrakeECM sends a signal to the selector and proportional valves which ENGAGE the brake of theaffected wheel. When the condition has improved and the ratio between the right and left axlesreturns to 1:1, the Brake ECM sends a signal to RELEASE the brake.


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The service brake pressure switch provides an input signal to the Brake ECM from theTransmission/Chassis ECM through the CAT Data Link and performs two functions:

1. When the service brakes or retarder are ENGAGED, the TCS function is stopped.

2. The service brake pressure switch provides the input signal needed to perform adiagnostic test. When the TCS test switch and the retarder lever are ENGAGEDsimultaneously, the TCS will engage each rear brake independently. Install twopressure gauges on the TCS valve, and observe the pressure readings during the testcycle. The left brake pressure will decrease and increase. After a short pause, the rightbrake pressure will decrease and increase. The test will repeat as long as the TCS testswitch and the retarder lever are ENGAGED.

The TCS valve has left and right brake release pressure taps. When the proportional solenoid isENERGIZED, Cat ET will show 68% when the brake is FULLY ENGAGED.

NOTE: During the diagnostic test, the parking/secondary brakes must be released.


Shown is the right rear wheel speed sensor (arrow) looking toward the rear of the truck. TheTCS monitors the drive wheels through four input speed signals: one at each drive axle, andtwo at the transmission output shaft.

The transmission output speed sensors monitor the ground speed of the machine and provideinput signals to the Brake ECM through the CAT Data Link. The TCS uses the transmissionoutput speed sensors to disable the TCS when ground speed is above 19.3 km/h (12 mph).

210


The TCS valve is mounted inside the left frame rail toward the rear of the machine. Twosolenoids are mounted on the valve.

Electrical signals from the Brake ECM cause the selector solenoid valve (1) to shift and selecteither the left or right parking brake. If the selector valve shifts to the left parking brakehydraulic circuit, the control oil is drained. The left reducing spool of the control valve canthen shift and engage the parking brake.

The proportional solenoid valve (2) controls the volume of oil being drained from the selectedparking brake control circuit. The rate of flow is controlled by a signal from the Brake ECM.

The pressure taps (3) can be used to test the left and right brake release pressures whenperforming diagnostic tests on the TCS. At HIGH IDLE, the pressure at the taps in the TCSvalve will be approximately 138 kPa (20 psi) less than the brake release pressure tested at thewheels.

The pressure taps are also used to provide parking brake dragging information to the servicetechnician. If the parking brakes are released, as sensed by the secondary brake pressure switchon the parking brake control valve, and parking brake pressure is below 3445 kPa (500 psi), aparking brake dragging event will be logged in the Brake ECM. The event can be viewed withCat ET.

211


3

3

2

1

212

This illustration shows the TCS valve with the engine running and the brakes RELEASED.

With the engine running, oil flows from the parking brake accumulator to the parking brakevalve. When the operator moves the transmission lever out of the PARK position, the BrakeECM energizes the parking brake solenoid which directs oil flow to the TCS valve.

In the TCS valve, oil flows through a screen and orifices to the selector solenoid and the brakereducing valves. When the TCS is not activated, the oil is blocked at the selector solenoid. Oilpressure moves the brake reducing solenoids to the left and oil from the brake charging pump isdirected to the parking brakes. The parking brakes are RELEASED.


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213

This illustration shows the TCS valve with the engine running and the left brake ENGAGED.

When signals from the sensors indicate that the left wheel is spinning 60% faster than the rightwheel, the Brake ECM sends a signal to the selector solenoid valve and the proportionalsolenoid valve. The selector solenoid valve shifts up to open a passage between the right endof the left brake pressure reducing valve and the proportional solenoid valve.

The pressure reducing valve provides signal oil to the drain ball check which allows oil fromthe TCS valve to return to the tank.

The proportional solenoid valve opens a passage from the selector solenoid valve to drainthrough the drain ball check. The proportional solenoid valve also controls the rate at whichthe oil is allowed to drain. Control circuit oil drains through the selector valve and enters theproportional valve.


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The reducing valve spool for the left parking brake shifts and blocks oil flow to the parkingbrake. Oil in the left parking brake control circuit begins to drain and the left parking brakebegins to ENGAGE. The left brake orifice restricts the flow of oil from the parking brakevalve.

When the signals from the sensors indicate that the left wheel is no longer spinning, the BrakeECM stops sending signals to the selector solenoid and the proportional solenoid. The selectorsolenoid valve and proportional solenoid valve block the passage to drain and allow the controlcircuit pressure to increase.

The left brake reducing valve spool shifts to the left and blocks the passage to drain. Parkingbrake oil is directed to the left parking brake and the brake is RELEASED.


CONCLUSION

This presentation has provided a basic introduction to the Caterpillar 773F/775F Off-highwayTrucks. All the major component locations were identified and the major systems werediscussed. When used in conjunction with the service manual, the information in this packageshould permit the technician to analyze problems in any of the major systems on these trucks.

214



1. Model view (right side)2. Model view (left side)3. Model view (front 775F)4. Model view (rear 775F)5. Walk around inspection6. Every 10 hours or daily inspection7. Front wheel bearing 8. Front suspension grease outlet fitting9. Brake linings

10. Primary fuel filter11. Dual engine oil filters12. Hoist and brake hydraulic tank13. Final drives14. Rear suspension cylinders15. Body up retaining pins16. Fuel level sight gauge17. Torque converter and transmission

charging filter18. S•O•S tap19. Brake oil filer20. Oil filter bypass switch21. Manual engine shutdown switch22. Battery disconnect switch23. Engine disconnect switch24. Engine lockout control switch25. Jacket water coolant sight gauge26. Radiator cap27. Steering system hydraulic tank sight

gauge28. Steering system oil filter29. Air intake system components30. Windshield washer reservoir31. Operator's compartment 10 hour or daily

checks32. Cab air filter33. Operator's station34. Truck Production Management System

(TPMS)35. Front dash panel (left side)36. Retarder lever37. Shift console38. Overhead console39. Floor pedals40. Fuse panels41. 773/775/f Electronic System block

diagram

42. Instrument cluster and VIMS/Advisordisplay panel

43. Instrument cluster (front dash panel)44. Instrument cluster gauges and indicators45. Messenger Display Module46. Messenger menu screen47. Performance screen submenu48. Performance menu49. Total menu selections50. Settings menu selection51. Service menu selection52. Service menu diagnostic events53. Service mode password menu54. Advisor/VIMS graphical display module55. Introduction screen after machine start-

up56. Main screen57. Transmission/Chassis ECM "pop-up"

warning screen58. Advisor home menu selections59. Operator menu60. Select profile screen61. Operator menu selection62. Service menu63. Calibrations submenu64. Service menu - diagnostics submenu65. Service menu - calibrations submenu66. Service menu - service parameters

submenu67. Settings menu68. Settings menu - display setup69. Payload menu70. Payload state - loading71. Monitor menu72. Monitor - Parameter Screen 173. Grade menu74. Grade menu - percentage of the grade

value75. Service mode menu76. Service Mode - enable or disable77. C27 engine with ACERT™ technology78. Engine ECM system diagram79. Engine ECM80. Coolant temperature sensor81. Crankshaft speed/timing sensor

VISUAL LIST


82. Cam speed/timing sensor83. Loss of engine speed/timing signal84. Throttle position sensor85. Prelubrication (QuickEvac) pump86. Ether start system87. High coolant temperature derate88. C11-C32 engine intake manifold

temperature derate89. Low oil pressure90. Air inlet restriction derate91. Fuel temperature derate92. Fuel filter restriction derate - Fuel Temp

above 30° V (86° F) and fuel pressureabove 138 kPa (20) psi

93. Engine compression brake94. Engine compression brake hydraulic

circuit - compression brake OFF95. Engine compression brake schematic96. Arc power and compression braking

level vs time97. Cooling system98. Water pump99. Cooling system flow100. Engine oil system101. Fuel system102. Fuel transfer pump103. Differential fuel pressure switch104. Fuel filter base105. Fuel cooler106. Low pressure fuel system107. Trim code files108. Injector trim file109. Air intake and exhaust system110. Turbocharger inlet pressure sensor111. Turbocharger - turbine side112. ATAAC core113. Turbocharger outlet pressure sensor114. Exhaust system115. Air induction and exhaust system116. Power train117. Power train electronic components118. Power train hydraulic system119. Torque converter - converter drive120. Torque converter - direct drive

121. Two-section power train pump122. Torque converter lockup clutch123. Lockup clutch modulating valve - torque

converter drive124. Lockup clutch modulating valve - direct

drive125. Torque converter and transmission

charging filter126. Filter bypass switch127. Transmission hydraulic system -

NEUTRAL128. ECPC transmission hydraulic controls129. Transmission modulating valves130. Engagement of transmission clutches131. Transmission modulating valve - NO

COMMANDED SIGNAL132. Transmission modulating valve -

COMMANDED SIGNAL BELOWMAXIMUM

133. Transmission modulating valve -COMMANDED SIGNAL ATMAXIMUM

134. Main relief valve135. Magnetic inspection plug136. Rear axle breather137. Differential138. Transmission/Chassis Electronic Control

System inputs and outputs139. Transmission/Chassis ECM140. Transmission shift lever circuits141. Transmission output speed sensors142. Engine speed sensor143. Body up switch144. Transmission/Chassis ECM - systems

controlled by ECM145. Steering system146. Steering system oil level sight gauge147. Steering system oil filter148. High pressure cut-off valve149. Flow compensator valve150. Steering pump - LOW PRESSURE

STANDBY151. Steering pump - MAXIMUM FLOW152. Steering disable valve location153. Steering disable solenoid valve

VISUAL LIST


154. Steering valve155. HMU for 773F/775F156. Electric secondary steering pump and

motor157. Pump and motor assembly158. Steering hydraulic system - LOW

PRESSURE STANDBY159. Hoist system160. Hoist lever161. Hoist lever position sensor162. Hoist and brake hydraulic tank163. Hoist and brake hydraulic tank - rear

view164. Hoist pump165. Hoist pump pressure tap166. Hoist control valve167. Pressure reducing valve168. Raise and lower solenoid valve169. Hoist cylinder lower circuit pressure tap170. Hoist control valve. - HOLD171. Hoist control valve. - RAISE172. Hoist control valve. - LOWER/POWER

DOWN173. Hoist control valve. - FLOAT174. Hoist control valve. - SNUB175. Two-stage hoist cylinders176. 773/775 hoist and brake cooling

schematic177. Brake system178. Rear brakes179. Caliper disc brake180. Brake charging pump181. Hoist pump182. Brake system filter183. Accumulator charging valve184. Brake ECM185. Accumulator charging valve - CUT-IN186. Accumulator charging valve - CUT-OUT187. 773F/775f brake accumulators188. Cab brake manifold189. Service brake pedal190. Service brake valve191. Manual retarder lever192. Rear slack adjuster193. Brake slack adjuster

195. Parking brake valve196. Left parking brake tap197. Secondary brake pedal position sensor198. Brake retract pump section199. Diverter (towing) valve location200. Relief valve201. 773/775 hoist and brake cooling

schematic202. Brake oil cooler203. Brake cooling oil pressure taps204. Brake hydraulic system205. Brake control module system diagram206. Brake ECM207. Service/retarder brake circuit - BRAKES

RELEASED208. Automatic retarder control (ARC)209. Traction control system (TCS)210. Wheel speed sensor (right rear)211. Selector solenoid valve212. TCS valve - Engine running / BRAKES

RELEASED213. TCS valve - Engine running / LEFT

BRAKE ENGAGED214. Conclusion

VISUAL LIST

HYDRAULIC SCHEMATIC COLOR CODE

This illustration identifies the meanings of the colors used in the hydraulic schematics and cross-sectional views shown throughout this presentation.


Dark Gray - Cutaway section

Light Gray - Surface color

Red - High pressure oil

Red/White Stripes - 1st pressure reduction

Red Crosshatch - 2nd reduction in pressure

Pink - 3rd reduction in pressure

Red/Pink Stripes - Secondary source oil pressure

Orange - Pilot, charge, or Torque Converter oil

Orange / White Stripes -Reduced pilot, charge, or TC oil pressure

Green - Tank, sump, or return oil Blue - Trapped oil

Brown - Lubricating oil

Purple - Pneumatic pressure

Orange Crosshatch - 2nd reduction inpilot, charge, or TC oil pressure.

White - Atmosphere orAir (No pressure)

Yellow - Moving or activated components

Cat Yellow - (Restricted usage)Identification of componentswithin a moving group

Black - Mechanical connection. Seal

Green / White Stripes -Scavenge Oil or Hydraulic Void

HYDRAULIC SCHEMATIC COLOR CODE

Red

- H

igh

Pres

sure

Oil

Red

/ W

hite

Str

ipes

- 1

st P

ress

ure

Red

uctio

n

Pink

- 3r

d R

educ

tion

in P

ress

ure

Red

/ Pi

nk S

trip

es -

Seco

ndar

y So

urce

Oil

Pres

sure

Ora

nge

- Pilo

t, C

harg

e or

Tor

que

Con

vert

er O

il

Blu

e - T

rapp

ed O

il

Bro

wn

- Lub

ricat

ing

Oil

Cat

Yel

low

- (R

estr

icte

d U

sage

)

Gre

en /

Whi

te S

trip

es -

Scav

enge

/ Su

ctio

n O

il or

Hyd

raul

ic V

oid

Iden

tific

atio

n of

Com

pone

nts

with

in a

Mov

ing

Gro

up

Bla

ck -

Mec

hani

cal C

onne

ctio

n. S

eal

Dar

k G

ray

- Cut

away

Sec

tion

Ligh

t Gra

y -

Surf

ace

Col

or

Whi

te -

Atm

osph

ere

or A

ir (N

o Pr

essu

re)

Purp

le -

Pneu

mat

ic P

ress

ure

Yello

w -

Mov

ing

or A

ctiv

ated

Com

pone

nts

Ora

nge

/ Cro

ssha

tch

- 2nd

Red

uctio

n in

Pilo

t,C

harg

e, o

r TC

Oil

Pres

sure

Ora

nge

/ Whi

te S

trip

es -

Red

uced

Pilo

t, C

harg

e, o

rTC

Oil

Pres

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Red

Cro

ssha

tch

- 2nd

Red

uctio

n in

Pre

ssur

e

Gre

en -

Tank

, Sum

p, o

r Ret

urn

Oil

HYD

RA

ULI

C S

CH

EMAT

IC C

OLO

R C

OD

E

SERV1830 - 240 - Handout No. 101/07

Machine Daily Inspection Checklist

Directions: Use this sheet and the Operation and Maintenance Manual when performing the dailyinspection as part of the machine orientation lab exercise.

Place a check in the blank after the task is performed.

_____ Back-up Alarm - Test

_____ Brake, Indicators, and Gauges - Test

_____ Braking System - Test

_____ Cooling System Level - Check

_____ Differential and Final Drive Oil - Check

_____ Engine Air Filter Service Indicator - Inspect

_____ Engine Oil Level - Check

_____ Fuel Tank Water and Sediment - Drain

_____ Fuel System Water Separator - Drain

_____ Hoist, Converter, and Brake Tank Oil Level - Check

_____ Seat Belt - Inspect

_____ Secondary Steering - Test

_____ Steering System Oil Level - Check

_____ Transmission Tank Oil Level - Check

SERV1830 - 241 - Handout No. 201/07

Machine Maintenance Locations

Place a check in the blank after locating the following maintenance items.

Filter Locations:

_____ Brake oil filter

_____ Steering pump oil filter (case drain)

_____ Steering system oil filter

_____ Transmission and torque converter charge oil filter

_____ Air conditioner filter

_____ Cab air filter

_____ Engine oil filters

_____ Engine air filters

_____ Engine crankcase breather

_____ Secondary fuel filter

_____ Primary fuel filter

_____ Fuel tank breather

_____ Differential and final drive breather

Sampling Valve Locations:

_____ Engine oil

_____ Hoist, converter, and brake oil

_____ Transmission oil

_____ Steering system oil

What is used to take oil samples of the differential, final drive, and front wheel?

_________________________________________________________________

SERV1830 - 242 - Handout No. 301/07

Sampling Port Locations:

_____ Differential and final drive

_____ Front wheel

Instrument Cluster Component Identification

SERV1830 - 243 - Handout No. 401/07

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Brake system check

Power train system check

Action lamp

Electrical system

Body up

Transmission in reverse

High beam

Transmission oil temperature gauge

Secondary steering engaged

Truck speed

LCD display window

Primary steering loss

Service hour meter

Traction control system engaged

Retarder engaged

Engine coolant temperature gauge

Machine immobilizer

Throttle lock

Engine rpm

Machine lockout active

Park brake engaged

Check engine

Brake oil temperature gauge

Fuel level gauge

Active gear and direction

List the number of each gauge or indicator:

Engine Component Identification

_____ Fuel injectors

Function:

Location:

_____ Coolant temperature sensor

Function:

Location:

_____ Fuel pressure sensor

Function:

Location:

_____ Intake manifold temperature sensors

Function:

Location:

_____ Atmospheric pressure sensor

Function:

Location:

_____ Turbo outlet (boost) pressure sensors

Function:

Location:

SERV1830 - 244 - Handout No. 501/07

Engine Component Identification (continued)

_____ Engine oil pressure sensor

Function:

Location:

_____ Speed/timing sensors

Function:

Location:

_____ Engine ECM

Function:

Location:

_____ Ground level shutdown switch

Function:

Location:

_____ Secondary fuel filter

Function:

Location:

_____ Primary fuel filter

Function:

Location:

SERV1830 - 245 - Handout No. 601/07

Engine Component Identification (continued)

_____ Fuel temperature sensor

Function:

Location:

_____ Differential fuel pressure switch

Function:

Location:

_____ Engine compression brake assemblies

Function:

Location:

_____ Air filter restriction sensors

Function:

Location:

SERV1830 - 246 - Handout No. 701/07

Power Train Component Identification

_____ Pump group

Function:

Location:

_____ Transmission and torque converter charge oil filter

Function:

Location:

_____ Lockup clutch modulating valve

Function:

Location:

_____ Torque converter outlet relief valve

Function:

Location:

_____ Torque converter inlet relief valve

Function:

Location:

_____ Torque converter outlet temperature sensor

Function:

Location:

SERV1830 - 247 - Handout No. 801/07

Power Train Component Identification (continued)

_____ Transmission main relief valve

Function:

Location:

_____ Transmission modulating valves

Function:

Location:

_____ Transmission oil cooler

Function:

Location:

_____ Transmission hydraulic oil temperature sensor

Function:

Location:

_____ Transmission/Chassis ECM

Function:

Location:

_____ Engine speed sensor

Function:

Location:

SERV1830 - 248 - Handout No. 901/07

Power Train Component Identification (continued)

_____ Torque converter oil temperature sensor

Function:

Location:

_____ Transmission input speed sensor

Function:

Location:

_____ Transmission output speed sensors

Function:

Location:

SERV1830 - 249 - Handout No. 1001/07

Steering System Component Identification

_____ Steering pump

Function:

Location:

_____ Steering valve

Function:

Location:

_____ Steering disable valve

Function:

Location:

_____ HMU

Function:

Location:

_____ Steering cylinders

Function:

Location:

_____ Secondary steering pump

Function:

Location:

SERV1830 - 250 - Handout No. 1101/07

Steering System Component Identification (continued)

_____ Steering tank

Function:

Location:

_____ Primary steering pressure switch

Function:

Location:

_____ Secondary steering pressure switch

Function:

Location:

SERV1830 - 251 - Handout No. 1201/07

Hoist System Component Identification

_____ Hoist pump

Function:

Location:

_____ Hoist control valve

Function:

Location:

_____ Hoist and brake hydraulic tank

Function:

Location:

_____ Hoist cylinders

Function:

Location:

_____ Hoist lever position sensor

Function:

Location:

_____ Hoist raise solenoid valve

Function:

Location:

SERV1830 - 252 - Handout No. 1301/07

Hoist System Component Identification (continued)

_____ Hoist lower solenoid valve

Function:

Location:

_____ Brake cooling relief valve

Function:

Location:

SERV1830 - 253 - Handout No. 1401/07

Brake System Component Identification

_____ Brake charging pump

Function:

Location:

_____ Accumulator charging valve

Function:

Location:

_____ Brake accumulators

Function:

Location:

_____ Cab brake manifold

Function:

Location:

_____ Brake oil filter

Function:

Location:

_____ Rear slack adjuster

Function:

Location:

SERV1830 - 254 - Handout No. 1501/07

Brake System Component Identification (continued)

_____ Service brake valve

Function:

Location:

_____ Retarder lever

Function:

Location:

_____ Parking brake valve

Function:

Location:

_____ TCS valve

Function:

Location:

_____ Service brake pedal position sensor

Function:

Location:

_____ Secondary brake pedal position sensor

Function:

Location:

SERV1830 - 255 - Handout No. 1601/07


_____ Brake retract pump

Function:

Location:

_____ Diverter (towing) valve

Function:

Location:

_____ Brake oil cooler

Function:

Location:

_____ Brake ECM

Function:

Location:

_____ Accumulator oil pressure switch

Function:

Location:

_____ TCS test switch

Function:

Location:

SERV1830 - 256 - Handout No. 1701/07


_____ ARC switch

Function:

Location:

_____ Brake compression switch

Function:

Location:

_____ Front brake lockout switch

Function:

Location:

_____ Rear wheel speed sensors

Function:

Location:

SERV1830 - 257 - Handout No. 1801/07

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SERV1830 - 264 - Handout No. 2501/07

Posttest1. When the engine lockout mode is activated, which of the following conditions exist:

A. engine starter is disabledB. secondary steering is disabledC. prelube function is disabledD. All of the above

2. The air conditioner filter is located:

A. on the left side of the cabB. on the right side of the cabC. on the front of the cabD. on the rear of the cab

3. The monitoring system includes how many warning categories

A. 2B. 3C. 4D. 5

4. How many main menus are available for navigation on the Messenger menu screen?

A. 3B. 4C. 5D. 6

5. Which of the following Messenger menus is used to determine when scheduled maintenance isrequired?

A. Performance menuB. Totals menuC. Settings menuD. Service menu

6. What information is NOT displayed when viewing diagnostic events on the Messenger displaypanel?

A. SRC (Source ID)B. CodeC. OCC (number of occurrences)D. Parameter

SERV1830 - 265 - Handout No. 2601/07

Posttest (continued)7. When a "pop-up" warning screen is displayed on the Advisor display, which of the following is

true?

A. Acknowledging the warning will clear the warning from the ECM's memoryB. Acknowledging the warning will only clear the warning from the Advisor screenC. If the warning is acknowledged the warning no longer remains activeD. None of the above

8. The calibrations menu in the Advisor Monitoring System allows calibration of which of thefollowing:

A. truck payloadB. injectorsC. pressure sensorsD. hoist solenoid valve

9. The monitor menu option in the Advisor Monitoring System allows the user to view how manyparameters at one time?

A. 1B. 2C. 3D. 4

10. Each compression brake assembly controls how many cylinders?

A. 1B. 2C. 3D. 4

11. When the Engine ECM commands a MEDIUM braking level, the compression brake is activatedfor how many cylinders?

A. 4B. 6C. 8D. 12

12. Pilot oil used to actuate the hoist solenoid valves is supplied by the:

A. pressure reducing valveB. parking brake release filterC. hoist pumpD. lockup clutch valve oil circuit

SERV1830 - 266 - Handout No. 2701/07

Posttest (continued)13. Which of the following components is located on top of the transmission planetary gears?

A. Transmission main relief valveB. Transmission modulating valvesC. Transmission hydraulic oil temperature sensorD. All of the above

14. Which of the following sensors checks the speed of the drive shaft to the speed of the engine?

A. Engine speed sensorB. Transmission input speed sensorC. Transmission output speed sensorsD. Torque converter output speed sensor

15. When the machine lockout switch is activated, which of the following actions occurs?

A. HMU oil flow is blockedB. Steering pump is disabledC. Steering disable solenoid valve is energizedD. All of the above

16. Which of the following is not installed on 773F/775F trucks?

A. Brake cooling pumpB. Brake oil coolersC. Brake cooling relief valveD. All of the above

17. The ARC system uses the rear service brakes and the ______________________ to automaticallycontrol truck speed.

A. TCSB. parking brakesC. front caliper type brakesD. None of the above

SERV1830 - 267 - Handout No. 2801/07

Posttest (continued)18. The front service brake solenoid directs oil to the front service brakes. What component directs

oil to the rear service brakes?

A. Service brake valveB. ARC solenoidC. Diverter valveD. Both A and B

19. Oil is provided to the diverter valve by the:

A. brake cooling pumpB. service brake accumulatorsC. parking brake accumulatorD. hoist pump

SERV1830 - 268 - Handout No. 2901/07

Posttest Answer Key1. D2. A3. C4. C5. B6. D7. B8. A9. D

10. B11. C12. A13. D14. B15. C16. A17. D18. D19. C

SERV1830 - 269 - Handout No. 2901/07

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