793F Brake Chassis Valve HELP-REV03

8/17/2019 793F Brake Chassis Valve HELP-REV03

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793F E.H. CHASSIS VALVE

(Electro – Hydraulic Chassis Valve Diagnostic Supplement)

TESTING & ADJUSTING PLUS

TROUBLESHOOTING TIPS

This document is a “Supplement” Guide!

Always refer to the latest information available from

Caterpillar SIS - using SSP serial # prefix, when

troubleshooting any EH Chassis Valve Issues.

Finning (Canada)Technical Training REV03. P.BAUER

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System Pressure Release

Hydraulic System

WARNINGPersonal injury can result from hydraulic oil pressure and hot oil.

Hydraulic oil pressure can remain in the hydraulic system after the

engine has been stopped. Serious injury can be caused if this pressure is

not released before any service is done on the hydraulic system.

Make sure all of the attachments have been lowered; oil is cool before

removing any components or lines. Remove the oil filler cap only when

the engine is stopped, and the filler cap is cool enough to touch withyour bare hand.

Brake

To relieve the pressure from the brake circuit, move the engine start switch to the OFF

position. This will activate a solenoid valve in order to release the hydraulic brake pressure

from the brake accumulators.

Brake Accumulators

WARNING

Hydraulic accumulator contains gas and oil under high pressure.

Improper removal or repair procedures could cause severe injury. To

remove or repair, instructions in the service manual must be followed.

Special equipment is required for testing and charging.

REFER MEDIA NUMBERS: KENR8738 , KENR8579 UNDER THE APPROPRIATE

HEADINGS FOR THE BRAKE SYSTEM ACCUMULATOR (SERVICE / PARKING).

Relieving the pressure in the brake circuit will not release the nitrogen precharge pressure

in the brake accumulators.

TOOLING GROUP REQUIRED: CATERPILLAR ELECTRONIC TECHNICIAN (E.T),COMMUNICATION ADAPTOR GROUP & ADAPTOR CABLE ASSEMBLY.

DIGITAL PRESSURE GROUP – PART # 198 – 4240 AND APPROPRIATE TRANSDUCERS.


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Do you know what you are looking at

and what to look for….?

1. Visual inspection is vital for the correct operation of

the “Full Hydraulic Brake System” on the 793F.

BRAKE E.C.M. SOFTWARE FILE #__________________

Model:_________________ Date:___________

Serial Number:___________Service Meter

Hours:_____________

Visual Inspection

Hose Connections:ComponentDamage

Oil Leaks: Oil Temperature: At least 55 Celsius

Oil Level in Brake Actuation Tank:

Nitrogen Charge Pressure in ALL Brake Accumulators

(1000 psi - +/- 50 psi) @ 21 Degrees Celsius ____________ Psi

Brake Holding Ability Test (1)

Engaged Brake Engine Speed (rpm) Engaged Brake Engine Speed (rpm)

Service Brake Parking Brake

Manual Retarder Secondary Brake

( 1 )The engine speed should reach a minimum of 1400 rpm before there is any machine movement.


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793F BRAKE CONTROL VALVE LAY-OUT

Standard Control Valve # 285-5630

(1) Diverter valve (front service brakes)

(2) Diverter valve (rear service brakes)

# 343-3181 XLP USES # 343-3182

(3) Solenoid valve (brake pump unloader)

# 343-3181 XLP USES # 343-3182

(4) Port for the service brake accumulator

# 262-1955

(5) Plug (orifice for feedback dampening of diverter valve (9)

(6) Port (parking brake pressure sensor)

(7) Filter cartridge

(8) Port for the parking brake accumulators

# 2949048

(9) Diverter valve for the parking and secondary brake

(10) Port for the pressure sensor for the oil supply

# 343-3185

(11) Orifice for the brake charging "OR1"

PS2-Pressure Brake Pump

(12) Valve (brake pump unloader)

# 221-4511

(13) Plug "RAX"

# 223-0016

(14) Port for return to tank “T2”

797F ONLY

The front and rear relays / diverters are serviced as akit. They are matched to open at the same time. AlsoDiverter (1) for the front brakes, when the XLP is beingused, check that the

******VERY IMPORTANT NOTE******

322-3795

pilot assembly is underit. The pilot assembly is what makes the front brake

pressure 80% of the rear (except when ARC is active).


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XLP Brake Control Valve Part

#2839559 uses a different Diverter

Valve for the Front & Rear Service

Brakes.


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(15) Port for the supply oil for the service brakes

(16) Check valve (service brake accumulator)

(17) Port "BCD" -

# 163-1829

(18) Plug (orifice for return oil from diverter valve (2)

NOT USED ON “793F” OR “797F”


(20) Port for the rear service brakes


(22) Port for the front service brakes

(23) Solenoid valve (front automatic retarder control)

(24) Plug (orifice for pilot oil for diverter valve (1)

# 279-6527

(25) Solenoid valve (rear automatic retarder control)

(26) Port for the pilot oil for the hoist

# 279-6527

(27) Port for the oil for the check valve for the TCS

(28) Port for the parking and secondary brakes

FRONT BRAKE COOLING DIVERT

SOLENOID IS NOT USED ON THE

793F OR 797F, BUT IS INSTALLED

CAN BE USED FOR

TROUBLESHOOTING A FAILED CO

ELSEWHERE ON THE VALVE.


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(29) Port for return oil for the service brake valve "T1"

(30) Solenoid valve for the parking and secondary brake


(32) Control valve (traction control signal)

# 279-6527

(33) Shuttle valve (rear service brake)

# 171-5704

(34) Shuttle valve (front service brake)

# 294-9050

(35) Port for the return to tank

# 294-9050

(36) Main relief valve

(37) Port for the supply oil

# 320-8118

(38) Solenoid valve for purging the brake accumulator’s

(39) Plug (orifice for purging the parking brake accumulators)

# 294-9049

NOT USED ON 793F or 797F, th

is the same as the “BRAKE

ACCUMULATOR PURGE” Soleno

valve Item # 38


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(40) Port for the pressure sensor for the parking brake accumulator

(41) Pressure reducing valve (pilot oil)

PS 1

(42) Check valve (parking brake accumulator)

# 294-9047

# 163-1829


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(43) Port for the pilot oil from the service brake pedal

(44) Port for the pressure switch for the front brakes(45) Port for the pressure sensor for the service brake accumulator

(46) Port for return oil

PS 3

(47) Plug (orifice for the return oil from diverter valve (2)(48) Plug


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(49) Plug (orifice for purging the service brake accumulator)

# 4 STORB PRESSURE TAP CAN BEPLACED HERE TO READ “SECONDARY

/ PARKING BRAKE” ACCUMULATOR

PRESSURE


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(1) Diverter valve (front service brakes)

(2) Diverter valve (rear service brakes)

(3) Solenoid valve (brake pump unloader)(4) Port for the service brake accumulator


(6) Port (parking brake pressure sensor)

(7) Filter cartridge

(8) Port for the parking brake accumulators

(9) Diverter valve for the parking and secondary brake

(10) Port for the pressure sensor for the supply oil


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(11) Orifice for the brake charging "OR1"

(12) Valve (brake pump unloader)

(14) Port for return to tank "T2"

(15) Port for the supply oil for the service brake

(16) Check valve (service brake accumulator)

(17) Port "BCD" NOT USED ON THE 793F & 797F


(20) Port for the rear service brakes


(22) Port for the front service brakes

(23) Solenoid valve (front automatic retarder control)


(25) Solenoid valve (rear automatic retarder control)

(26) Port for the oil for the hoist valve

(27) Port for the oil for the check valve for the TCS

(28) Port for the parking and secondary brakes

(29) Port for return oil for the service brake valve "T1"

(30) Solenoid valve for the parking and secondary brake


(32) Control valve (traction control signal)

(33) Shuttle valve (rear service brake)

(34) Shuttle valve (front service brake)

(35) Port for the return to tank

(36) Main relief valve

(37) Port for the supply oil

(38) Solenoid valve for purging the brake accumulators

(39) Plug (orifice for purging the parking brake accumulators)

(40) Port for the pressure sensor for the parking brake accumulator(41) Pressure reducing valve (pilot oil)

(42) Check valve (parking brake accumulator)

(43) Port for the pilot oil from the service brake pedal

(44) Port for the pressure switch for the front brakes

(45) Port for the pressure sensor for the service brake accumulator

(49) Plug (orifice for purging the service brake accumulator)


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LIVE TESTING SPECIFACATIONS

Test Specifications Actual

Value

Accumulator “Cycle Time” After System is Fully Charged,

minimum of 10 cycles30 Seconds

Accumulator Nitrogen Charge Pressure for the Service

Brake & Park Brake

1000 ± 50 psi

at

21° C (70° F)

Cut-In Pressure for the Service Brake 2100 ± 70 psi

Cutout Pressure for the Service Brake 3000 ± 70 psi

Service Brake Pressure at the Slack Adjusters for the StandardWheel Groups (Front & Rear) 675 ± 60 psi

Service Brake Pressure at the Slack Adjusters for the

Extended Life Wheel Groups

FRONT

525 ± 87 psi

REAR

670 - / + 58 psi

Retarder Brake Pressure at the Slack Adjusters for the

Standard Wheel Groups (Front & Rear) 675 ± 116 psi

Retarder Brake Pressure at the Slack Adjusters for the

Extended Life Wheel Groups

FRONT525 ± 116 psi

REAR

670 -/+ 116psi

Park Brake Release Pressure for the Secondary Brake System680 ± 70 psi

Towing Valve Pressure (within 120 seconds of turning motoron)

550 to 650 psi

Main Relief Valve Pressure 3250 ± 50 psi

Pressure for the Pressure Reducing Valve (Pilot Oil)600 -50 + 0 psi

Pilot Pressure for the Service Brake Pedal 718 ± 22 psi

NOTE: When the pump is at Low Idle condition, the cycle time is denoted as the time between Cut-

out and Cut-in pressure. Quicker than 30 seconds on a fully charged system = LEAKAGE


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WHAT IS THE DIFFERERENCE BETWEEN “STANDARD & “XLP”

If the truck is equipped with the Extended Life Power

Train (XLP option), the front brakes are equipped with

three additional brake disc packs and the brake / chassis

Valve includes an additional piston and sleeve. Since the

surface area of the piston is smaller than the surface area

of the service brake relay valve, the relay valve directs a

reduced oil pressure to the brake piston. The reduced

pressure is necessary due to the additional brake disc

packs in the XLP option.

The service brakes on the truck with the additional

retarding will have three more discs and plates. The

standard retarding front brakes are equipped with 10

discs in the front and 15 discs in the rear. Additional

retarding will have 13 discs in the front with the standard

15 in the rear. To develop the proper proportion during

additional retarding, the brake chassis valve will beequipped with an additional sleeve and piston.


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THIS IS ONLY USED ON BRAKE CHASSIS CONTROL VALVE PART # 283-9559


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E.H. CONTROL VALVE PRESSURE CHECKS AND

AJUSTMENTS.

# 3: Brake Filter

#4: Pressure Tap for Main System Pressure & Stand-By

Pressure.

SPECS: Maximum System Pressure = 3250 psi - / + 50 psi

Stand-By System Pressure = 150 psi +/- 150 psi

• To see what the main system pressure is set to, go to

the Brake ECM & override the parameter to OFF for

the “Brake Pump Un-loader Solenoid” & observe

what reading you have on your gauge.


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• Do not run test for any longer than 15 seconds.(Or

you can just un-hook the two pin connector on the

Solenoid)

• To see what your stand –by pressure is set at, let the

system run at low Idle and cycle a few times. Then

read what is on your gauge after system cut –out

takes place.

• The only adjustment that can be made is for Main

System Pressure, corrections are made on the main

system relief valve. Item #2

PLEASE NOTE:

Also when checking accum ulator charging, use a gauge to

check the sensors in ET. The sensors could be causing the

cut in / cut o ut to be off .

A low main relief valve cou ld also cause a stal led charge

where you wou ldn' t cut out.

“ If th is is happening, then p erform the fol lowing tests”


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1. Brake Control Valve

2. Main System Relief

3. Brake Filter

4. Pressure Tap

5. Brake pump Un-loader Solenoid

6. Lock-nut

7. Adjustment Screw

CUT-IN & CUT-OUT PRESSURE

• This pressure is measured at two different places,

first one being on a pressure tap (A) located on the

“Service Brake Accumulator” port and the second

being on the “Parking Brake Accumulator” port

pressure tap (B)

NOTE: E.T. Not required for this test

(1)

Install manual gauge.

(2)

Disconnect 2 pin connector.

(3)

Read manual gauge.

(4)

Re-connect 2 pin connector.


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PRESSURE TAP “A” SERVICE BRAKE

ACCUMULATOR PRESSURE


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• This pressure is not adjustable and is controlled by

the Pump Un-loader Solenoid & Diverter Valve.

• The pressure setting (after a few system cycles) for

the cut-out is (3000 ± 70 psi). The cut-in pressure is

70 percent of the cutout pressure. The cut-in

pressure will be (2100 ± 70 psi).

REMOVE THIS PLUG AND INSTALL

STORB # 4 ADAPTOR & PRESSURE

TAP TO READ “PARKING BRAKE

ACCUMULATOR PRESSURE”

PRESSURE TAP “B”


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6V-3965 Test Fitting & #4 STOB

MALE to #6 STOB FEMALE Adaptor.

Notice the recess area, to allow

installation into the recessed port in

the “Brake Valve”

Modified “PARKER” Test Fitting #4

STOB, notice the recess machined at

one end.


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Leakage

When the pump is at the low idle setting, the pressure

will cycle between the cut-in pressure and the cut-out

pressure. The cycle should occur in Approximately 30seconds @ an operating temperature of Approximately

55 degrees Celsius or better. If this cycle occurs in less

than 30 seconds, there is leakage in the system that must

be corrected. (HOIST LEVER IN HOLD)

1. Start the engine. Allow the brake accumulators to

charge fully. Minimum of 10 cyclesNote: Once the brake accumulators are fully charged, the

cycle between the cut-in and cutout pressure will

increase to 30 seconds.

2. To locate the cause of the excessive leakage, shut

down the engine with the engine shutdown control. Do

not shut down the engine with the ignition key. Theengine shutdown switch is located on the right side of

the machine near the right hand ladder.

3. The pressure in the brake accumulators will decrease

because of leakage in the system and lubrication. If there

is a significant leak, one system will decay more rapidly.

4. Observe the pressure at the accumulators.

Note: Before any components are removed, make sure

that the brake accumulators have been fully discharged.


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If the pressure for the service brake accumulator drops

rapidly, check the following items:Check valve for the service brake

Diverter valve for the service brakes

Solenoid valve for the ARC

Pressure relief valve

Solenoid valve for purging the brake accumulators

Solenoid valve for the brake cooling diverter "BCD"Control valve for the TCS

Hoist control valve

If the pressure for the parking brake accumulator drops

rapidly, check the following:

Diverter valve for the parking brakeSolenoid valve for the parking brake

Solenoid valve for purging the brake accumulators

Control valve for the TCS

Check valve for the parking brake

PLEASE NOTE: Als o on a 793F the primary (Service) should

always bleed off b efore the secondary (Parking ). So thatdoesn 't tel l you th ere is an excessive leak on th e primary

side. If secondary does fal l as fast as or faster than the

pr imary side that would be a clue you have a leak on the

secon dary accum ulators. 797F's have 4 accum ulators and

may have more balanced leak dow n rates.


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(3) Diverter valve (un-loader)(4) Solenoid valve (un-loader)

(5) Plug (orifice for pilot oil diverter valve for un-loader)

If the pressure does not reach the standby pressure for

the brake system, perform the cut-in and the cutout test.

If the pressure at Cut-out (3000 psi) for the brake system

is incorrect, inspect diverter valve (3), solenoid valve (4),

and the orifice of plug (5).


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P.R.V. (PILOT OIL) PRESSURE

• Pilot oil is used for the Hoist Control / Brake

Cooling Valve.

Place gauge @ this pressure tap to

ecord Pilot Oil Pressure. 600 psi


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• Make sure hoist control lever (A) is in the

“HOLD” position.

• If pilot system pressure requires correction,

make adjustment at Item #2- Pilot Relief Valve.

•

Turn adjustment screw clockwise to increasepressure, anti-clockwise to decrease pressure.

Park Brake release pressure: Is controlled by a

Proportional Solenoid Valve & Diverter Valve,

which uses main system pressure. Park brakerelease pressure is checked at pressure tap #2

and the pressure on the gauge must be at 680 ±

70 psi.


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Service Brake Pilot & Application Pressure Check

(1)Pressure tap, Next Page

(2)On this page = Pressure Tap

(2) Control Valve and Mounting, Next Page

(3) Brake accumulator for the service brakes, Next Page

(4) Brake accumulator for the parking brakes, Next Page


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Install at pressure tap item #1, with machine running and

brake system fully charged. Make a few service brake

applications then with the service brake fully depressed,

record your value on the gauge – should be:

718 ± 22 psi

This pressure is also controlled by a Proportional

Solenoid Valve & Diverter Valve, which uses main system

pressure.


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Slack Adjusters (1)

Slack Adjuster Pressure At The Slack Adjuster (2) Pressure At The Wheel (3)

Front Slack Adjuster

Left Front Wheel

Front Slack Adjuster

Right Front Wheel

Rear Slack Adjuster

Left Rear Wheel

Rear Slack AdjusterRight Rear Wheel

( 1 )The pressures should be approximately the same value.

( 2 )Use the pressure tap on the slack adjuster.

( 3 )Measure this pressure at the port that is labeled. "S"

NOTE: Your readings will depend on what Braking System

you are working with “STANDARD” / “XLP”

RESIDUAL SLACK ADJUSTER PRESSURE

Residual oil pressure at the Front & Rear wheels should

be approximately 3.6 to 8.0 psi. Max

NOTE: Low residual pressure indicates a failed slack

adjuster. High residual pressure may indicate a failed

slack adjuster or wrapped brake discs.

Documents

793F Brake Chassis Valve HELP-REV03