15,000 miles
(24,000 kilometers)

Drag Link

See Vehicle Manufacturer

GREASE

NLGI
GRADE

OUTSIDE TEMPERATURE

2

Refer to the lubricant manufacturer’s
specifications for the temperature
service limits applicable to your area.

Multipurpose Grease
SAE 80W-90 GL-5

NOTE: L ubrication greases acceptable for use on the STEERTEK axle will carry a designation of NLGI #2 EP and rated GC-LB or equivalent.

KINGPIN LUBRICATION
STEERTEK NXT upper kingpin grease zerks are located on the inboard side of the steering knuckle
and upper kingpin connection, see Figure 7-1. On some models of the STEERTEK NXT a grease
zerk is located on the bottom of lower steering knuckle on the inboard side.
FIGURE 7-1

FIGURE 7-2

Upper
Grease Zerk

1. Place vehicle on a level floor.
2. Chock the wheels.
3. Raise the vehicle and support the frame
with frame stands.
4. Prior to greasing the kingpins on the vehicle, the suspension must be in a loaded c­ ondition.
5. Clean off all the grease zerks and grease gun tip with a clean shop towel prior to l­ubrication.
6. Lubricate the kingpins through the grease zerks on the top and bottom of the steering knuckle,
see Lubrication Specification chart above.

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AIRTEK® for Tiffin Motorhome Chassis
7. Force the required lubricant into the upper and lower kingpin grease zerks, until new lubricant
flows out from the upper kingpin connection and steering knuckle and the thrust bearing
purge location, see Figure 7-2.
NOTE

Greasing at the lower zerk should purge grease from the thrust bearing shell. The left and right
side of the AIRTEK for Tiffin Motorhome Chassis system have steel roller thrust bearing.

TIE ROD END LUBRICATION
1. Place vehicle on a level floor.
2. Chock the wheels.
3. Raise the vehicle and support the frame with frame stands.
4. Turn the vehicle wheels straight ahead.
5. Wipe the grease zerk and grease gun tip with clean shop towels.
6. Wipe the seal / boot clean with shop towels.
7. Attach a grease gun to the grease zerk. Either a hand or pneumatic grease gun is acceptable.
If air operated grease gun is used, system air pressure should not exceed 150 psi (1035 kPa).
FIGURE 7-3

EXCEEDING THE MAXIMUM AIR PRESSURE TO
THE GREASE ZERK CAN CAUSE DAMAGE TO THE
DUST BOOT CAUSING COMPONENT FAILURE.

8. Dirt, water, and discolored old grease
should flow from the relief vents or purge
holes near the boot crimp or bellows
area, see Figure 7-3. Continue to purge
grease until fresh grease flows from the
purge area.
9. If the tie rod end is designed for lube
service and it will not accept grease proceed as follows:

Dust Boot
Boot Crimp

Zerk Fitting

a. Remove the grease zerk.
b. Inspect the threaded grease zerk hole in the tie rod end and remove any obstructions.
c. Install a new grease zerk.
d. Continue the lubrication procedure.
e. If the tie rod end will not accept grease following this procedure it will be necessary to
replace the tie rod end. Refer to Tie Rod End replacement in Component Replacement
Section of this publication.
10. Apply grease until all the old grease is purged from the boot and fresh grease is coming out.

TIE ROD END
INSPECTION PROCEDURE
Before beginning this inspection procedure, the entire system must be unloaded (i.e., the front
end of the vehicle must be raised and supported with safety stands).
DO NOT GREASE THE TIE ROD ASSEMBLY BEFORE PERFORMING THE INSPECTION. DOING SO CAN
INHIBIT EFFORTS TO DETERMINE ACTUAL WEAR.
REPLACE THE ENTIRE TIE ROD END IF THE BOOT IS TORN OR MISSING, FAILURE TO DO SO CAN CAUSE
PREMATURE WEAR OF THE TIE ROD END.
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1. Block rear wheels of vehicle. Using the bottom of the axle beam or the frame rails, raise the
front end off the ground and support with stands.
2. With the engine off, turn the wheels from full left to full right and then return to the straightahead position.
3. Check that the boots are in place and completely installed over the tie rod ends.
4. Check for cracking or tears in the boots. Also check the boot seals for damage. Replace the
entire tie rod end if the boot is damaged.
THE COTTER PIN MUST BE INSTALLED CORRECTLY THROUGH THE TIE ROD END WITH THE CASTLE NUT
TIGHTENED TO THE PROPER TORQUE SPECIFICATION IN ORDER TO SECURELY ATTACH THE TIE ROD.
LOSS OF THE COTTER PIN CAN CAUSE THE TIE ROD END NUT TO BECOME LOOSE AND ADVERSELY
AFFECT VEHICLE STEERING AND POSSIBLY RESULT IN TOTAL LOSS OF STEERING CONTROL.

5. Check that the tie rod end nut is installed and secured with a cotter pin. If the cotter pin is missing, check the nut torque specification and then install a new cotter pin. Always tighten the castle
nut to specified torque when setting the cotter pin. DO NOT back off the nut to insert cotter pin.
IT IS CRITICAL TO CHECK THE 5⁄ 8" TIE ROD CLAMP BOLT HEAD LOCATION TO VERIFY THE CLAMP
FASTENERS HAVE SUFFICIENT CLEARANCE AWAY FROM THE LOWER SHOCK MOUNT AT FULL WHEEL
CUT. THE FASTENERS MUST NOT CONTACT THE LOWER SHOCK MOUNT. FAILURE TO DO SO CAN
CAUSE ONE OR MORE COMPONENTS TO FAIL CAUSING LOSS OF VEHICLE CONTROL AND POSSIBLE
PERSONAL INJURY OR PROPERTY DAMAGE.

6. Verify the 5⁄8" tie rod clamp bolt head does not contact the lower shock mount at full wheel
cut, see Figure 7-4.
FIGURE 7-4
5/8"

Tie Rod Clamp Bolt
It is critical to check the 5/8" tie rod clamp bolt head
location to verify the clamp fasteners have sufficient
clearance away from the lower shock mount at full
wheel cut. The fasteners must not contact the
lower shock mount.

Tie Rod Cross Tube Slots
It is critical to have the threaded portion of the tie
rod end extend past the slots in the tie rod cross tube.

Threaded Portion
of the Tie Rod End

5/8" Tie

Rod Clamp Locknut
Tightening Torque 68 ± 7 ft. lbs. (92 ± 9 Nm)

THE THREADED PORTION OF THE TIE ROD END MUST EXTEND PAST THE SLOTS INTO THE TIE ROD
CROSS TUBE, SEE FIGURE 7-4. FAILURE TO DO SO CAN CAUSE COMPONENT DAMAGE, LOSS OF
VEHICLE CONTROL AND POSSIBLE PERSONAL INJURY OR PROPERTY DAMAGE.

7. Check that the tie rod end is threaded correctly into the cross tube and is engaged deeper
than the end of the cross tube slot. The tie rod end must be visible the entire length of the
cross tube slot, see Figure 7‑4.
8. Check that grease zerks are installed. Replace a damaged grease zerk with a new one.
DO NOT USE THE FOLLOWING ITEMS OR METHODS TO CHECK FOR MOVEMENT OF THE TIE ROD
ASSEMBLY, WHICH CAN CAUSE DAMAGE TO COMPONENTS:
■■ A CROW BAR, PICKLE FORK OR 2 X 4.
■■ ANYTHING OTHER THAN HANDS USED TO GRASP AND ROTATE THE CROSS TUBE ASSEMBLY (CAN

RESULT IN DAMAGE TO THE CROSS TUBE).
■■ EXCESSIVE PRESSURE OR FORCE APPLIED TO THE TIE ROD ENDS OR THE JOINTS OF THE ASSEMBLY.
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AIRTEK® for Tiffin Motorhome Chassis
9. By hand or using a pipe wrench, with jaw protectors to avoid gouging the cross tube, rotate the
cross tube toward the front of the vehicle and then toward the rear. After rotating, center the cross
tube. If the cross tube will not rotate in either direction, replace both tie rod ends, see Figure 7-5.
10. Position yourself directly below the tie rod end. Using both hands, grab the assembly end
as close to the tie rod end as possible (no more than 6" or 152.4 mm). Apply hand pressure with reasonable human effort vertically up and down in a push-pull motion several
times, using approximately 75 ± 25 foot pounds of force. Check for any movement or
looseness at both tie rod end locations, see Figure 7-6.
FIGURE 7-5

FIGURE 7-6

11. If there is any movement in the tie rod assembly, install a magnetic based dial indicator on the
Ackermann arm, see Figure 7-7.
12. Set the dial indicator to zero.
13. Apply hand pressure with reasonable human effort vertically up and down in a push-pull motion
several times, using approximately 75 ± 25 foot pounds of force. Observe the reading on the
dial indicator.
FIGURE 7-7

14. If the reading is more than 0.060", replace both
tie rod ends at the next service i­nterval.
15. If a tie rod end exhibits ≥ 0.125" of movement
by hand, the vehicle should be removed immediately from use and replace the tie rod end.
NOTE

According to the Commercial Vehicle Safety
Alliance (CVSA), the “out of service” criteria for
front steer axle tie rod assemblies on any commercial vehicle is: Any motion other than rotational
between any linkage member and its attachment
point of more than 1⁄ 8" (3 mm) measured with
hand pressure only. (393.209(d)), (published
in the North American Standard Out-of-Service
Criteria Handbook, April 1, 2006.)

HEIGHT CONTROL VALVE
Refer to component manufacturer for height control valve inspection and adjustment procedures.

BRAKES AND WHEEL BEARING END PLAY
Refer to component manufacturer for wheel bearing end play inspection and wheel bearing
adjustment procedures, see Parts List Section under Brake Assembly for contact information.

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AIRTEK® for Tiffin Motorhome Chassis
CLAMP GROUP RE-TORQUE
LOOSE OR OVER TORQUED FASTENERS CAN CAUSE COMPONENT DAMAGE, LOSS OF VEHICLE
CONTROL, PROPERTY DAMAGE, OR SEVERE PERSONAL INJURY. MAINTAIN CORRECT TORQUE VALUES
AT ALL TIMES. CHECK TORQUE VALUES ON A REGULAR BASIS AS SPECIFIED.

1. Clamp group locknuts must be torque to specification at preparation for delivery.
2. Clamp group locknuts must be re-torqued at 1,000 miles (1,609 km).
3. Thereafter follow the 6 month / 25,000 miles (40,000 km) visual inspection and annual retorque interval.
4. Ensure that the clamp group is properly aligned and the hex bolts are seated in the top pad,
and the top pad / bottom axle wrap is centered on the axle spring seat / top axle wrap, see
Figures 7-8 and 7-9.
5. Check for the signs of component or bolt movement.
6. If signs of movement are present, disassemble the clamp group fasteners, check for component wear or damage and replace as necessary, then install new clamp group fasteners and
repeat Steps 1 through 5.
7. Tighten the clamp group locknuts evenly in 50 foot pounds increments in the proper pattern,
see Figure 7‑10, to achieve uniform bolt tension to 295 ± 10 foot pounds torque.
FIGURE 7-8

FIGURE 7-9

FIGURE 7-10

IMPORTANT

IMPORTANT

Ensure that the ¾" Clamp Bolts
are seated properly in the Top Pad

Ensure that Axle
Clamp Group is
properly aligned

¾" Clamp Group Locknuts
Tightening Torque
295 ± 10 ft. lbs. (400 ± 13 Nm)

KINGPIN BUSHING
INSPECTION PROCEDURE (STEERING KNUCKLE LATERAL MOVEMENT)
1. Chock the wheels to help prevent the vehicle from moving. Set the parking brake.
2. Use a jack to raise the vehicle until the wheels are off the ground. Support the vehicle with
safety stands.
3. CHECKING THE UPPER KINGPIN BUSHING. Install the base of a dial i­ndicator onto the axle
beam and place the tip against the steering knuckle, see Figure 7‑11.
4. Set the dial indicator to “0” zero.
5. Move the top of the tire in and out by applying reasonable constant pressure and then release,
see Figure 7-13.
6. Check the reading on the dial indicator. If the dial indicator moves more than 0.015", the
upper bushing is worn or damaged. Replace both bushings. Refer to the Kingpin Bushing
replacement procedure in the Component Replacement Section of this publication.
7. CHECKING THE LOWER KINGPIN BUSHING. Install a dial indicator so that the base is on the axle
and the indicator tip is against the inside of the bottom of the knuckle, see Figure 7-12.
8. Set the dial indicator to “0” zero.

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FIGURE 7-11

FIGURE 7-12

CHECKING UPPER KINGPIN BUSHING

CHECKING LOWER KINGPIN BUSHING

FIGURE 7-13

9. Move the bottom of the tire in and out. If
the dial indicator moves more than 0.015",
the lower bushing is worn or damaged.
Replace both kingpin bushings. Refer to
the Component Replacement Section of
this publication.
NOTE

If one (1) bushing is worn or damaged, it is
mandatory to replace both the top and bottom
bushings on that knuckle assembly.

STEERING KNUCKLE
CHECKING VERTICAL END PLAY (UP AND
DOWN MOVEMENT)
The operating spec for vertical end play on the
steering knuckle is 0.008" to 0.030".
FIGURE 7-14

1. Chock the rear tires to help prevent the vehicle from moving.
2. Set the parking brakes.
3. Use a jack to raise the vehicle until both tires are 1" off the ground.
4. Place a dial indicator on each side of the axle as follows:
a. Index the wheels slightly (left or right).
b. Place the magnetic dial indicator base on the axle, see Figure 7-14.
c. Place the tip of the dial indicator on the top of the upper steering knuckle
(not on the grease cap).
5. Set the dial indicator to “0” (zero).
6. Lower the jack.
7. If vertical end play is greater than 0.030", or below 0.008" an adjustment of the
upper knuckle is necessary.

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AIRTEK® for Tiffin Motorhome Chassis
8. ■ If the vertical end play is greater than 0.030", loosen the socket head cap screws and
push down on the knuckle assembly until the proper vertical end play is achieved.
■■

If the vertical end play is less than 0.008", loosen the socket head cap screws and pull
up on the knuckle assembly until the proper vertical end play is achieved.

9. Retighten the socket head cap screws to

188 ± 12 foot pounds torque.

SURFACE PAINT WEAR
FIGURE 7-15

FIGURE 7-16

Rear Shackle Plate — The Hendrickson
AIRTEK suspension system equipped on Tiffin
Motorhome Vehicles, utilizes rubber bushings
in the leaf springs. These rubber bushings
allow the leaf spring to deflect and may
contact the shackle plates when the vehicle
encounters high lateral acceleration (e.g. a
highway clover leaf). The rubber bushing will
center the leaf spring between the legs of
the shackle plates once the vehicle is driven
straight.

Rear Shackle
Plate

This function of the rubber bushing may allow
the leaf spring to contact the rear shackle
plate and possibly remove surface paint from the contact area, see Figure 7-15. Surface paint
wear does not cause damage that will affect the function or durability of the rear shackle plate or
their mating components when a minimum wall thickness is maintained.
Rear Shackle Plate
minimum thickness 5.8 mm

INSPECTION
An indication that the rear shackle plates are worn and require replacement is when the thickness
decreases to 5.8 mm or less, see Figure 7-16.
FIGURE 7-17

SHOCK ABSORBER
NOTE

It is not necessary to replace shock absorbers in pairs if only
one (1) shock absorber requires replacement.
Hendrickson uses a long service life, premium shock absorber
on all AIRTEK suspensions. When the shock absorber replacement is necessary, Hendrickson recommends that the shock
absorbers be replaced with identical Hendrickson Genuine
parts for servicing. Failure to do so will affect the suspension
performance, durability, and will void any applicable ­warranty.
See vehicle manufacturer’s applicable publications for other
shock absorber inspection requirements.
Inspection of the shock absorber can be performed by
doing a heat test, and a visual inspection. Replace as necessary, refer to the Component Replace­ment Section of this
publication.

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HEAT TEST
1. Drive the vehicle at moderate speeds on rough road for minimum of fifteen minutes.
DO NOT GRAB THE SHOCK ABSORBER AS IT COULD POSSIBLY BE HOT AND CAUSE PERSONAL INJURY.

2. Use an infrared thermometer to check the temperature of the shock absorber. This can also
be performed by carefully touching the shock absorber body below the dust cover. Touch the
frame to get an ambient reference, see Figure 6-19. A warm shock absorber is acceptable, a
cold shock absorber should be replaced.
3. To inspect for an internal failure, remove and shake the suspected shock absorber. Listen for
the sound of metal parts rattling inside. Rattling of metal parts can indicate that the shock
absorber has an internal failure and the shock absorber should be replaced.

VISUAL INSPECTION
FIGURE 7-18

Look for these potential problems when doing a visual inspection. Inspect the shock absorbers
fully extended. Replace as necessary.
SHOCK ABSORBER VISUAL INSPECTION - UNACCEPTABLE CONDITIONS

LEAKING VS. MISTING SHOCK ABSORBER VISUAL INSPECTION
FIGURE 7-19

The inspection must not be conducted after driving
in wet weather or a vehicle wash. The shock absorber
needs to be free from water. Many shock absorbers are
often misdiagnosed as failures. Misting is the process
whereby very small amounts of shock absorber fluid
evaporate at a high ­o perating temperature through
the upper seal of the shock absorber. When the “mist”
reaches the cooler outside air, it condenses and forms a
film on the outside of the shock absorber body. Misting
is perfectly normal and necessary function of the shock
absorber. The fluid which evaporates through the seal
area helps to lubricate and prolong the life of the seal.
NOTE

AIRTEK systems are equipped with a premium seal on the
shock absorber, however this seal will allow for misting
to appear on the shock absorber body (misting is not a
leak and is considered acceptable).
Inspect the shock absorber fully extended. A shock absorber that is truly leaking will show signs
of fluid leaking in streams from the upper seal. These streams can easily be seen, underneath
the main body (dust cover) of the shock absorber. Replace as necessary.

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AIRTEK® for Tiffin Motorhome Chassis
TIRE INSPECTION
The leading causes of tire wear are the following, in order of importance:
a. Tire Pressure
b. Toe Setting
c. Thrust Angle
d. Camber
■■ The following tire Inspection guidelines are based upon Technology & Maintenance Council

(TMC) recommended practices. Any issues regarding irregular tire wear where Hendrickson
is asked for assistance, will require tire and alignment maintenance records, reference TMC’s
literature numbers RP 219A, RP 230, or RP 642.

■■ Tire wear is normally the best indicator of vehicle alignment condition. If tires are wearing too

rapidly or irregularly, alignment corrections may be needed. The tire wear patterns described
below can help isolate specific alignment problems.

■■ The most common conditions of concern are:

The most common conditions of concern are:
■■ Overall Fast Wear (Miles per 32nd)

■■ Diagonal Wear

■■ Feather Wear

■■ Rapid Shoulder Wear (One Shoulder Only)

■■ Cupping

■■ One-Sided Wear

FIGURE 7-20

OVERALL FAST WEAR
(Miles per 32nd)

Overall Fast Wear — Fast wear can be described as exhibiting a good, but accelerated wear pattern. It is typically caused by operating conditions, such as mountainous terrain, frequency and
severity of turning, abrasive road surfaces in combination with vehicle configurations and their
attributes-such as power steering, heavy axle loads, high wheel cuts, setback axles, short wheel
base tractors, long wheel base straight trucks. To correct this problem, consult with vehicle and tire
manufacturers when specifying equipment or replacing tires. For more information, see TMC RP
219A publication, page 11. For information on how to accurately measure and record tire rates,
see TMC RP 230 publication.

FIGURE 7-21

FEATHER WEAR

Feather wear — Tread ribs or blocks worn so that one side is higher than the other resulting in
step-offs across the tread face. Generally, ribs or blocks exhibit this wear. To spot this problem, do
the following:
With one hand flat on the tread of the tire and a firm down pressure, slide your hand across the
tread of the tire. In one direction, the tire will feel smooth and in the opposite direction there will
be a sharp edge to the tread. Typical causes of feather wear include: excessive side force scrubbing, resulting from conditions of m
­ isalignment such as excessive toe, drive axle misalignment,
worn, missing or damaged suspension components, bent tie rods or other chassis misalignment.
To correct this problem, tires can be rotated to another axle for maximum utilization of remaining
tread. Additionally, diagnose the vehicle itself and correct misalignment condition as required. If
steer tire feathers are in opposite directions, an improper toe condition is most likely the cause.
For more information, see TMC RP 219A publication, page 5.
If feather wear on both steer tires is in the same direction, drive axle or other chassis ­misalignment
is indicated. If one steer tire shows feather wear and the other steer tire has normal wear, a combination of toe and drive axle or chassis misalignment is indicated.

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FIGURE 7-22

RAPID SHOULDER WEAR
(One Shoulder Only)

Rapid Shoulder Wear (One Shoulder Only) — Is defined as a tire worn on the edge of one shoulder, sometimes extending to inner ribs. It can progress to diagonal wipeout. For more information,
see TMC RP 219A publication, page 22.
This wear condition is usually caused by excessive toe or excessive camber. These conditions can
be created by a misaligned or bent axle and can also be caused by loose or worn wheel bearings.
To correct this type of rapid shoulder wear:
■■ Tires – Change direction of rotation of tire. If shoulder wear is severe, remove and retread
■■ Vehicle – Diagnose misalignment and / or mechanical condition and correct

FIGURE 7-23