L578 System maintenance - BENLEE SUSPENSION SYSTEM MAINTENANCE 3 L578 A Read the model number on the identification tag. The ride height, along with other product information, is included

TECHNICALPROCEDURETRAILER SUSPENSION SYSTEMS

SUBJECT: System MaintenanceLIT NO: L578DATE: September 2001 REVISION: A

®

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . .2

FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2TRI-FUNCTIONAL® BUSHING . . . . . . . . . . . . . .2Rigid-Axle Connection . . . . . . . . . . . . . . . . . .2Roll Stability . . . . . . . . . . . . . . . . . . . . . . . . .2Soft Riding . . . . . . . . . . . . . . . . . . . . . . . . . .2Load Control . . . . . . . . . . . . . . . . . . . . . . . . .2Durability . . . . . . . . . . . . . . . . . . . . . . . . . . .2

RIDE HEIGHT . . . . . . . . . . . . . . . . . . . . . . . . . . .2Factors Affecting Ride Height . . . . . . . . . . . . . .3

CENTER LIFT SUSPENSIONS . . . . . . . . . . . . . . . . .6

AIR CONTROL SYSTEM . . . . . . . . . . . . . . . . . . . .6Height Control Valve . . . . . . . . . . . . . . . . . . .6Air Dump Valves . . . . . . . . . . . . . . . . . . . . . .7

PERIODIC INSPECTION SCHEDULE . . . . . . . . . . . .7Original-Installation Inspections . . . . . . . . . . . .8Daily Inspections . . . . . . . . . . . . . . . . . . . . . .830-Day Inspection . . . . . . . . . . . . . . . . . . . . .890-Day Inspection . . . . . . . . . . . . . . . . . . . . .8QUIK-ALIGN® Inspection . . . . . . . . . . . . . . . . .8Wheel End Maintenance . . . . . . . . . . . . . . . . .8

SUSPENSION SYSTEMS MAINTENANCE . . . . . . . . .8Ride Height Adjustment . . . . . . . . . . . . . . . . .8Air Spring . . . . . . . . . . . . . . . . . . . . . . . . . . .9Shock Absorber . . . . . . . . . . . . . . . . . . . . . . .9Pivot Connection . . . . . . . . . . . . . . . . . . . . .10TRI-FUNCTIONAL BUSHING . . . . . . . . . . . . . .10

TROUBLESHOOTING: TRI-FUNCTIONAL BUSHING .11Commonly Misdiagnosed Bushing Problems .11

TORQUE SPECIFICATIONS . . . . . . . . . . . . . . . . .13

TABLE OF CONTENTS

TRAILER SUSPENSION SYSTEM MAINTENANCE

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INTRODUCTIONHendrickson Trailer Suspension Systems designs itssuspensions to provide low-maintenance operationand a long, safe life. The suspensions exhibit excellent ride characteristics under all legal load conditions. Your suspension was chosen to give yourtrailer the best ride, the correct load-carrying capability and the required amount of roll control foryour vehicle.

Hendrickson trailer air suspensions are manufacturedin modern, quality-oriented facilities. Great care istaken to ensure that our customers receive the bestproduct value for their purchasing dollar.

Hendrickson trailer air suspensions deliver durabilitywith a light-weight, simple and trouble-free design.The suspensions will cushion the trailer, cargo andthe driver with a quality ride not attainable without aHendrickson air-suspension system.

Hendrickson supplies a wide variety of trailer suspension designs to meet your application needs.Each suspension is intended for use in specific applications with maximum load capacities.

For a complete listing of Hendrickson products, contact your Hendrickson representative.

HENDRICKSON SUSPENSIONFEATURESTRI-FUNCTIONAL® BUSHINGSThe TRI-FUNCTIONAL BUSHING (located at the suspension pivot connection) controls vehicle roll-and axle-alignment, yet allows easy up-and-downtravel. It also controls forces generated by braking,accelerating and irregular road surfaces. Cavities orvoids in the rubber located at the top and bottom ofthe bushing absorb vertical movement. These cavitieshelp to increase roll stability by elongating duringoperation to absorb forces as the vehicle turns. Thebushing’s center portion (solid rubber molded arounda steel center sleeve) absorbs horizontal and lateralmovement. The bushing and suspension pivot connection are virtually maintenance free.

RIGID-AXLE CONNECTIONAll Hendrickson trailer axles are welded directly to thesuspension beams. This design has no flexible connections, which may lead to maintenance orreplacement due to instability. In addition to beingwelded, the HT series axle connection is also bolted.

The INTRAAX® series axle connection is integratedinto the suspension beams with a patented axle wrapand window weld for optimal structural integrity. Thesuspension beam mounting surface is machined andcontinuously welded to the axle wrap, eliminatingaxle seats and U-bolts. The INTRAAX rigid-axle connection provides outstanding roll stability, maintains axle alignment to the beam, and contributes to a straighter axle tube and controlled toealignment.

ROLL STABILITYThe TRI-FUNCTIONAL BUSHING and rigid-axle connection result in a roll-stable installation. The trailer floor remains level, even when the trailer is off-set loaded, with only one height control valve pertrailer.

SOFT RIDINGThe air springs and TRI-FUNCTIONAL BUSHINGS support the trailer load while simultaneously absorbing road shocks. This softer ride protects thedriver, cargo and vehicle; it also provides longervehicle life and greater driver comfort.

LOAD CONTROLWhen properly installed, the single height controlvalve helps to maintain an evenly distributed loadacross all axles. With the exception of tire deflection,the trailer’s ride height remains constant whetherloaded or unloaded.

DURABILITYHendrickson air suspensions and their componentshave been thoroughly tested to provide a long, virtually maintenance free life. Their sturdy construction has a history of proven durability.

RIDE HEIGHTRide height is the distance from the suspensionmounting surface to the center of the axle. AllHendrickson air suspensions are designed to operateat a specific ride height. Care must be taken toensure the correct loaded suspension ride height ismaintained while the trailer is in use.

To determine your Hendrickson suspension rideheight, locate the suspension identification tag. Thistag can be found:


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Read the model number on the identification tag. Theride height, along with other product information, isincluded in the model number. Refer to the followingmodel number examples for ride height identification(the bold number indicates ride height):

If you cannot determine the ride height from the information on the identification tag, contact theHendrickson technical service department at 800-455-0043 in the United States or 800-668-5360 inCanada. They will help you determine the designedride height of your suspension.

Changes in ride height affect the air spring height,which in turn changes the suspension’s load carrying capabilities. To help maintain load equalization among the axles, Hendrickson trailersuspensions are intended to be used at ride heightswhich maintain equal air spring heights throughoutthe application.

Operating a suspension at an incorrect ride heightcan result in improper loading and can shorten theservice life of the suspension. Hendrickson is notresponsible for components which fail due to incorrect ride height settings.

FACTORS AFFECTING RIDE HEIGHTThe following features need to be considered when determining ride height:

FRAME-TO-GROUND HEIGHTThe height from the bottom of the trailer frame (or suspension mounting surface) to the ground must bedetermined at each suspension location (Figure 1).This dimension provides the desired trailer deckheight.

TRAILER DECK HEIGHTThe suspension ride height is calculated by subtracting the LOADED tire radius from the LOADEDframe-to-ground height. The radius of the tire willdecrease as the trailer is loaded due to tire deflection,which in turn, affects the trailer deck height (Figure 2).

Suspension Suspension

Suspension mounting surface

Frame-to-ground Frame-to-ground

Deck height

Figure 1. Frame-to-ground-height


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Figure 3. Fifth wheel height

Suspension Suspension

Deck height

Fifth wheel height lower thandesign specifications Varying frame-to-ground heights

Figure 4. Frame deflection

Unloaded frame Deflection ofloaded frame

Frame-to-groundinstalled

Frame-to-groundunder load

Auxiliary airsuspension

Suspension mountingsurface

Figure 5. Frame-to-ground height (center lift axle)

Deck height

Loaded ride heightLoaded frame-to-ground

Figure 2. Trailer deck height

Center of axleTire

Ride height

Loaded tire

Loaded trailerframe-to-ground

height

Loaded deckheight


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FIFTH WHEEL HEIGHTThe tractor fifth wheel affects the height of the trailerframe (for example: a low fifth wheel height wouldcause the trailer frame to slope downward).Variations in the fifth wheel height will result in variations of suspension ride heights.

The correct suspension ride height must be determined at each suspension location (Figure 3).When ride height variations are required, contact theHendrickson trailer engineering department at 800- inthe United States or 800- in Canada to evaluate loadequalization capabilities.

FRAME DEFLECTIONDeflection of the trailer frame when loaded must be considered. Frame deflection will result in a suspension ride height different from the installed rideheight. The correct suspension ride height must bedetermined at each suspension location (Figure 4).When ride height variations are required, consult theHendrickson Trailer Engineering Department to evaluate load equalization capabilities.

FRAME-TO-GROUND HEIGHT (CENTER LIFT AXLES)The height of the bottom of the trailer frame (or suspension mounting surface) from the ground mustbe determined at each suspension location (Figure5). This dimension must provide the desired LOADEDdeck height.

A leaf spring suspension’s ride height will changeunder various loads. The auxiliary air suspension’sride height must be specified to match the loaded leafspring suspension’s ride height.

SUSPENSION TRAVELHendrickson Trailer Suspension Systems uses theseterms to define suspension travel:

Jounce: The maximum amount of upward axle travel, from ride height toward the frame,allowed by the suspension (Figure 6).

Rebound: Maximum amount of downward axle travel, from ride height toward the ground,allowed by the suspension (Figure 6).

When selecting a suspension, the amount of axletravel must be considered in both the loaded andunloaded conditions. Unloaded, the suspensionrebound must not be less than 2 in.

TIRE CLEARANCEIn selecting a suspension, the trailer’s tire clearancemust be used to determine the maximum suspensionjounce permitted by the trailer design. Hendricksonspecifies that the tire clearance above the jouncerequirement must include one inch for all HT andINTRAAX models (Figure 7). T series models requiretwo inches of tire clearance above the specifiedjounce requirement. A two inch clearance is specifiedbetween the trailer frame and inside tire inboard sidewall. This will provide sufficient clearance toallow for tire distortion and axle walk.

Figure 6. Suspension travel

Ride height

JounceRebound

Center of axle

Figure 7. Tire clearance

Center of axle

Ride height

Tire

Jounce + 1" = tire clearance


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The top dimensions in Figure 8 are for 35-in. suspension beam centers. The bottom dimensions(in parentheses) are for 41-in. suspension beamcenters.

CENTER LIFT SUSPENSIONSHendrickson offers center lift kits, which when addedduring a trailer suspension installation, provide a lift-ing capability (Figure 9). Only those suspensionswith a minimum of 4 in. of jounce are approved foruse with a center lift kit.

Hendrickson’s suspension jounce dimension includesan allowance for air spring bumper compression. Asa result, the amount of lifted up travel will be lessthan the jounce.

The suspension lift distance indicates the amount ofaxle up travel. The resulting clearance under the tirewill vary depending on both frame and tire deflection.

AIR CONTROL SYSTEMMany types of air controls are available forHendrickson trailer air suspensions. The most common system automatically regulates the designedride height by controlling the air pressure supplied tothe air springs. When used in conjunction with othertypes of suspensions, such as a leaf-spring suspension, an operator-controlled pressure regulatoris often employed. If using axle lifts or other specialfeatures, other air control circuits and componentsare added. All systems operate from the vehicle compressed air supply. The air pressure in the airsprings controls the height or load on the axle.

Figure 10 illustrates a typical air control arrangementused on Hendrickson trailer air suspensions. Oneheight control valve controls any number of primaryair suspensions. Contact the trailer manufacturer forspecific information about your trailer air control system.

HEIGHT CONTROL VALVEThe height control valve on the Hendrickson trailer air suspension automatically responds to the relativeposition of the axle and vehicle frame. It meters airinto or out of the air springs. Variations in load ortemperature only affect the adding or exhausting ofair. Since the Hendrickson trailer air suspension is amechanically stable suspension, only one heightcontrol valve is necessary. This system is less complex, less expensive and less troublesome thancompetitive systems.

Figure 8. Inside-to-inside tire measurements

46½"(56½")

Minimuminside-to-inside tireclearance

35"(41")

Suspensionbeamcenters

Area of thepivot bolt

49"(55")

If the potential existsfor tire interference,the QUIK-ALIGNshear-type bolt canbe installed from theoutboard side of theframe bracket.

Figure 9. Center lift suspension

Ride height

Lift(axle travel)

Center of axle

Tire clearance


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In addition, it provides a safer system should an airspring malfunction occur. Notice that only one heightcontrol valve is used per trailer or dolly; this groupingcan include two, three, four or more axles.Hendrickson generally recommends that the heightcontrol valve be positioned on the rear axle on tandem axle arrangements and on the center axle oftri-axle arrangements. For trailers equipped withSURELOK®, a ride height locking device, it is important to place the height control valve on thesame axle as the SURELOK mechanical support arms.

When the actuating lever of the height control valvemoves up, the valve opens and connects the air supply to the air spring. When the actuating levermoves down, the valve shuts off the air supply andopens the exhaust port to vent excess air from the airsprings. A check valve prevents the loss of air springpressure if the air supply fails. In the central position,air does not flow in or out of the air springs.

AIR DUMP VALVESAir dump (or exhaust) valves increase stability duringtrailer loading and unloading, as well as prolongcomponent life. The valves can be controlled automatically, manually or by the use of an air-pilotvalve.

When suspension air is exhausted, Hendrickson trailer air suspensions limit the suspension up travel(jounce) by a rubber bumper located inside the airspring. The air-spring bumpers adequately supportthe rated suspension capacity with the suspension airexhausted. Hendrickson approves using air dump

valves only when the control exhausts all the trailerair springs. Also, use of the air dump control isapproved for the following situations:

• A trailer parked for any length of time, loaded orunloaded, either when connected to the tractor orsupported by the landing gear legs.

• A trailer being loaded or unloaded, particularlywhen fork lift trucks are used.

• A dump trailer during the dump mode only.

• A trailer experiencing a sudden unloading of cargo,such as steel removed with a crane.

Any variation beyond these conditions must beapproved in writing by Hendrickson ApplicationsEngineering Department.

CAUTION: Due to the geometry of all trailingarm air suspensions, the trailer willmove forward when air is exhaustedfrom the suspension and the trailerbrakes are locked. If the trailer isresting on it’s landing gear, thismovement may damage or collapsethe landing gear. Always exhaust theair suspension before locking thebrakes.

Variations in trailer deck height and, therefore, thesuspension ride height will cause the longitudinalmovement of the trailer. When loading and unloadingthe trailer, the changes in the load supported by thesuspension will cause the deck height to change; thischange results in the trailer moving away from theloading dock. Unless the air is properly exhaustedfrom the air suspension, the above movement candamage or collapse the trailer landing gear, as wellas result in a potentially dangerous gap between thetrailer and the loading dock.

PERIODIC INSPECTION SCHEDULEThe Hendrickson trailer air suspension requires verylittle attention. Your air suspension may well last thelife of the vehicle by using the information in thispublication and other Hendrickson technical publications.

Figure 10. Height control valve

Height control valve

Air springs

To air supply

Brake protection valve


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ORIGINAL-INSTALLATION INSPECTIONSThe vehicle manufacturer is responsible for completing the installation to Hendrickson specifications. In your review of the vehicle for thefirst time, check that:

• the trailer is level• all welds are of acceptable quality• all bolts are in place and secure• the pivot connection hardware is properly

assembled:welded collar pivot connectionsthe pivot-connection nut is tack welded to thebolt threads (not required with “Huck” fastener)QUIK-ALIGN® pivot connectionslist all the proper connection requirements

• no component interferences exist

DAILY INSPECTIONSA quick look to verify a level trailer that is riding atthe correct ride height is suggested. This inspectionwill help you find any obvious problems. A closerinspection can detect broken or loose parts beforeany serious problems appear.

30-DAY INSPECTIONAt 30 days, inspect clearances around air springs,tires, shock absorbers and all other moving parts.Evidence of part interference requires immediateattention by a qualified mechanic. The 30-dayinspection includes checks to verify that:

• bolts are secure• axle connections are tight• no obvious sign of wear exists

If you have any questions about the suspension area,contact the trailer manufacturer or the Hendricksontechnical service department at 800-455-0043 in theUnited States or 800-668-5360 in Canada.

90-DAY INSPECTIONAt 90 days, thoroughly check all items that wereinspected at 30 days. The 90-day inspection alsoincludes checks to verify that:

• all welded connections are sound and there is nosign of deterioration

• frame attachment joints, crossmember structuresand all pivoting and clamping connections aresound

Early detection and correction of problems can save expenses and prolong the life of your trailer.

It is unlikely that you will find any problems with yourHendrickson air suspension during these inspections.However, your careful attention to these periodicinspections can save a great deal of time andexpenses by avoiding unexpected difficulties inremote locations. Contact your Hendrickson representative or the Hendrickson ApplicationsEngineering Department at (330) 456-7288 to discuss any questions about the construction and/oroperation of your Hendrickson trailer air suspension.

QUIK-ALIGN® INSPECTIONInspection of the QUIK-ALIGN occurs at 3,000 milesand at every lining change.

WHEEL END MAINTENANCE7,500 MILESVisually inspect seal and hub cap for leakages andhub oil level (if oil bath type).

12 MONTHS OR 100,000 MILESAt 12 months or 100,000 miles, which ever occursfirst, visually inspect seal and R&I hub cap. Visuallyinspect for contaminants; check wheel bearingadjustment; install new oil, if oil filled, and replacehub cap gasket-retorque. Repair if necessary.

SUSPENSION SYSTEMS MAINTENANCEBy correcting minor problems when found, yourHendrickson air suspension will provide excellentservice throughout your trailer’s life. This section willhelp you to determine what to expect from your suspension components and the proper maintenanceprocedures.

RIDE HEIGHT ADJUSTMENT1. Connect the vehicle to a compressed air supply

with approximately the pressure of the normalsupply system.

2. Ensure the inflation of the air springs.

3. Measure the ride height by using this method:

a. Measure from the underside of the trailerframe to the top of the axle

b. Add 2½ in. (half the diameter of the axle) tothe measurement


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Example: 11½ in. to the top of the axle with the2½ in. equals a 14 in. ride height.

4. Raise or lower the trailer as necessary, so it is atthe designed ride height.

5. Once the trailer is set to the correct designed rideheight, set the HCV lever to the neutral (central)position.

6. Adjust the HCV linkage to fit between HCV leverand lower linkage attachment.

IMPORTANT: When adjusting the height control valve,block the tire and release the trailerbrakes. The axle must rotate freely toavoid a false reading.

Some height control valves have very small openingsand a time delay of as much as 15 seconds. Allowsufficient time for the system to react to the adjustment. The response time will appear to belengthy, but be patient.

Once set to the designed ride height, test drive thetrailer. After the test drive, check the ride height toassure an accurate adjustment.

Notice that the use of one height control valveremoves the requirement for synchronization foundwith most other air suspension systems. This featurewill save you time and expense in servicing your airsystem.

If you have any questions regarding the operation ofyour Hendrickson trailer air system, contact theHendrickson technical service department at 800-455-0043 in the United States or 800-668-5360 inCanada.

AIR SPRINGSAir springs will last almost indefinitely in most applications. However air springs will fail quicklywhen rubbed, scuffed, or punctured. If an air springfails, the trailer will settle on the internal rubberbumpers, so you can proceed to the nearest servicefacility at a lower speed. You should try to determinethe cause of a failure, so you can avoid a costlyrepeat of the problem. If you have questions aboutthe cause of a failure, contact the Hendrickson technical service department at 800-455-0043 in theUnited States or 800-668-5360 in Canada.

To replace an air spring, follow these steps:

1. Exhaust all air from the suspension system.

2. Raise and support the vehicle in a safe manner.

3. Unbolt the air spring.

4. Disconnect air-supply lines.

5. Replace the air spring.

6. Bolt the air spring in place.

7. Connect the air-supply lines.

8. Lower the trailer to the ground.

9. Supply air to the suspension system.

SHOCK ABSORBERShock absorbers do not absorb shock, they absorbenergy to prevent suspension oscillation. Shockabsorbers are also used as rebound stops in most airsuspensions. The shock absorber limits the stroke ofan air spring, which prevents the air spring frombeing pulled apart. In some severe service applications, a shock strap or chain down stops areadded to additionally aid in limiting the stroke of anair spring.

To remove an air spring, follow these steps:

1. Remove the end fasteners.

2. Insert the new shock absorber.

3. Secure with correct size locknut and bolts.

4. Torque fasteners to specification.

If your suspension has unique travel requirements,use only Hendrickson shock absorbers for replacements.

CAUTION: Do not lift the trailer without theshock absorbers in place. If shockabsorbers are not in place,overextension of the air springs willoccur. Damage may occur to theoverextended air springs.


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IMPORTANT: Hendrickson trailer air suspensiondesign requires the use of specific airsprings and shock absorbers. Onlycomponents purchased fromHendrickson or a Hendrickson-approveddistributor can be used. Replacementwith other components may causepremature failures and void thewarranty.

PIVOT CONNECTIONA correct pivot connection is crucial to the life of the suspension. The pivot fastener must continually provide a sufficient clamp load through the bushingto prevent premature suspension failure.

Hendrickson trailer air suspension models comeequipped with either a “Huck”-type fastener or a conventional nut-and-bolt arrangement at this location.

“Huck”-type fasteners are installed using specializedhydraulic equipment. This fastener can only beremoved by cutting the fastener apart.

Other factory-installed units are equipped with a nutand bolt at the pivot connection. This arrangement isalso used when a field replacement is necessary. Thepivot bolts are torqued to 800 ft-lbs. The nut is tackwelded to the bolt threads to assure a permanentconnection.

Hendrickson INTRAAX suspension systems comeequipped with QUIK-ALIGN pivot connection hardware. The hardware consists of a specially plated shear bolt to ensure a proper clamp load,(550 ft-lbs, H-45 torque).

CAUTION: Failure to properly torque the pivotbolt or tack weld the pivot nut to thebolt will result in loss of warrantycoverage.

TRI-FUNCTIONAL BUSHINGHendrickson’s TRI-FUNCTIONAL BUSHING has unique properties that will provide years of maintenance-free service. The TRI-FUNCTIONAL BUSHING (located atthe suspension pivot connection) provides a resilientconnection that allows an axle to walk without excessive flexing. The TRI-FUNCTIONAL BUSHING, inconjunction with the rigid axle connection, results in

a roll-stable suspension design that resists trailerlean independent of the air spring loading.

There are times when a problem seemingly in thearea of the suspension is diagnosed as a failedbushing. Closer inspection typically reveals anothercomponent or a faulty installation is the problem. If aproblem is in the area of the suspension, refer to theTROUBLESHOOTING section on page 11. If a failedbushing is present, contact the Hendrickson technicalservice department at 800-455-0043 in the UnitedStates or 800-668-5360 in Canada.

Rebushing of a suspension requires the use of abushing removal/installation tool and bushing kit,containing the required components for rebushing.Contact Hendrickson for assistance. When rebushingthe suspension, refer to Hendrickson publicationL427, Bushing Replacement Procedures, for complete bushing replacement instructions.

IMPORTANT: Literature is also available for installingthe TRI-FUNCTIONAL BUSHING. Rebushusing only the lubricant supplied in thebushing kit by Hendrickson TrailerSuspension Systems.


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TROUBLESHOOTING: TRI-FUNCTIONAL BUSHINGCOMMONLY MISDIAGNOSED BUSHING PROBLEMSWhile the following problems can result from a failed bushing, most often they are the result of the items listed below.

IMPORTANT: Contact Hendrickson Technical Service Department at (330) 456-7288 for assistance.


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COMMONLY MISDIAGNOSED BUSHING PROBLEMS (CONTINUED)


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TORQUE SPECIFICATIONSUse these torque specifications when installing the fasteners covered below.

NOTE: Torque values are specified for the fasteners in the condition in which they are supplied by Hendrickson. DO NOT APPLY ANY ADDITIONAL LUBRICANTS.

CAUTION: Overtorquing could result in fastener failure.


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Information contained in this literature was accurate at the time of publication. Product changes may have been made after the copyright date that are not reflected.© 2008 Hendrickson USA, L.L.C. (U.S. Rights) Hendrickson International Corporation (Rights Outside U.S.) All Rights ReservedL578 Rev A 09-01

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Documents

L578 System maintenance - BENLEE SUSPENSION SYSTEM MAINTENANCE 3 L578 A Read the model number on the identification tag. The ride height, along with other product information, is included