ONE-SIDED WEAR

One-sided wear — Is excessive wear on one side of tire extending from the shoulder towards the
center of the tread. For more information, see TMC RP 219A, page 26.
One-sided wear is usually caused by improper alignment, worn kingpins, loose wheel bearings,
excessive camber, excessive axle loads, non-parallel axles, or non-uniform tire and wheel assembly caused by improper bead seating or bent wheel.
To correct one-sided wear:
■■ Tires – Depending on severity, rotate tires to another axle position or, if worn to minimum tread

depths, submit for possible retreading.

■■ Vehicle – Diagnose mechanical problem and correct.
FIGURE 7-24

Cupping — Localized, dished out areas of fast wear creating a scalloped appearance
around the tire. Cupping, which appears around the tire on the shoulder ribs, may also
progress to adjoining ribs, see TMC RP 219A publication, page 7.
Cupping is usually a result of moderate-to-severe imbalance, improper rim / wheel
mounting, excessive wheel end play or other assembly non-uniformity. It can also be
due to lack of shock absorber control on some suspension types.
To solve cupping problems:
■■ Tires – Correct mismount or balance problem. If ride complaints arise, steer tires

may be rotated to drive or trailer axle.

■■ Vehicle – Diagnose component imbalance condition, i.e., wheel, rim, hub, brake,

drum. Correct as necessary.

FIGURE 7-25

Diagonal Wear — Can be described as localized flat spots worn diagonally across the tread at approximately 25-35° angles, often repeating
around the tread circumference. For more information, see TMC RP 219A
­publication, page 20.
Diagonal wear is usually caused by bad wheel bearings, toe out, mismounting of tire and wheel assembly to axle, and mismatched duals for
size and / or inflation pressures. It may start as brake skid. Diagonal wear is
aggravated by high speed empty or light load hauls.
To correct diagonal wear, reverse direction of rotation of the tire. If wear is
excessive, true tire. If the source of trouble is the vehicle, diagnose cause
and correct as needed.

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Preventive Maintenance

AIRTEK® for Tiffin Motorhome Chassis
SECTION 8

Alignment & Adjustments
ALIGNMENT DEFINITIONS
FIGURE 8-1

Ackermann Steering Geometry — The geometry of the four bar
linkage consisting of the front axle beam pivot points, tie rod arms,
and cross tube and attempts to provide free rolling of front tires in a
turn. Ackermann geometry is dependent upon the steering axle
track-width and wheelbase of the vehicle. Improper geometry results
in wheel scrub in turns which generally appears as toe wear on the
tire. Usually more wear is present on one side of the vehicle than the
other due to the operational route of the vehicle.
Bump Steer (Feedback) — The feedback felt through the steering
linkage to the steering wheel when a steer axle tire hits a bump in
the road. This occurs because the axle-end of the drag link and the
axle attachment point of the spring do not travel in parallel circular
arcs as the suspension moves up and down. This condition can also
be caused by trapped air in the power steering system.

FIGURE 8-2

Camber — The angle formed by the inward or outward tilt of the
wheel reference to a vertical line. Camber is positive when the wheel
is tilted outward at the top and is negative when the wheel is tilted
inward at the top.
Excessive positive camber may cause smooth wear on the outer half
of the tire tread. Excessive negative camber may cause wear on the
inner half of the tread. Static-unloaded camber angles are built into
the axle to put the loaded tire perpendicular to the road.

FIGURE 8-3

Caster — The forward or rearward tilt of the steering axle kingpin in
reference to a vertical line. The angle is measured in degrees. Caster
is positive when the top of the steering axis is titled rearward and is
negative when the tilt is forward. Proper caster is important for directional stability and return ability. Too much positive caster can cause
shimmy, excessive steering effort and is normally a vehicle performance and handling consideration. Uneven positive caster may
create a steering pull toward the side with the lower caster. This attribute may be used to compensate for crowned roads.

Alignment & Adjustments

26

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AIRTEK® for Tiffin Motorhome Chassis
FIGURE 8-4

KINGPIN
INCLINATION
IN DEGREES

Kingpin Inclination (KPI) — The inward tilt of the kingpin from the vertical. This front
suspension parameter has a pronounced effect on steering effort and return ability.
As the front wheels are turned around an inclined kingpin, the front of the truck is
lifted. This lifting of the vehicle is experienced as steering effort when the turn is
executed and exhibits itself as recovery force when the steering wheel is released.
Kingpin Offset — The distance between the center of the tire patch and intersection
of the kingpin axis with the ground.This parameter of front end geometry is important
in vehicles without power steering and has a major effect on static steering. If there
is no kingpin offset, the tires must scrub around the center of the pin patch when
turned in a static condition, resulting in higher static steering efforts.
Steering Arm — The component that connects the drag link to the axle
knuckle assembly.

KINGPIN
OFFSET
FIGURE 8-5

Thrust Angle, Tracking, or Square — The angle formed by the
centerline of the vehicle frame (geometric centerline) and the
direction that an axle points. As indicated by the term “square”,
the ideal value for the angle is 0° or when the axle centerline is at
90° or perpendicular to the geometric centerline. Thrust or
tracking to the right is positive, and to the left is negative.
A steering correction is required to offset the effect of the thrust
angles and keeps the vehicle traveling in a straight line. It results
in a lateral offset between the steer and drive axle tires commonly
referred to as “dog tracking.”
Tie Rod Arm (Ackermann-Arm, Cross Tube Arm) — The component that
transmits steering forces between left and right axle knuckle assemblies
through the cross tube assembly.

FIGURE 8-6

TOE-IN

Toe-in — is when the horizontal line intersects in front of the wheels, or the
wheels are closer together in front than in the back. Toe-in is commonly designated as positive, toe-out as negative. Excessive toe-in wears the outside edge of
the tires. Steer axle toe is adjustable to reduce wear to the leading edge of the
tire and also to avoid road wander.Toe is adjusted in a static, unloaded condition
so that the tires will run in a straight line under a dynamic, loaded condition.

FIGURE 8-7

TOE-OUT

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Toe-out — Is when the horizontal lines intersect behind the wheels, or the
wheels are closer together in back than in front. Toe-in is commonly designated as positive, toe-out as negative. Excessive toe-out wears the inside
edge of the tires. Steer axle toe is adjustable to reduce wear to the leading
edge of the tire and also to avoid road wander. Toe is adjusted in a static,
unloaded condition so that the tires will run in a straight line under a
dynamic, loaded condition.

27

Alignment & Adjustments

AIRTEK® for Tiffin Motorhome Chassis
FIGURE 8-8

Toe-Out on Turns — (See Ackermann Geometry).
Excessive turning angles such as those encountered
in pickup and delivery operations may contribute to
premature tire wear. Be advised that the greater the
turning angles, the more that toe and camber change.
If you have any doubt regarding the optimum turning
angles for your operation, contact the vehicle’s manufacturer, axle OEM, tire OEM and alignment equipment
manufacturer for advice.
Total Toe — The angle formed by two horizontal lines
through the planes of two wheels. Steer axle toe Is
adjustable to reduce wear to the leading edge of the
tire and also to avoid road wander. Toe is adjusted in a
static, unloaded condition so that the tires will run in a
straight line under a dynamic, loaded condition.

TOE-OUT

TOE-IN

INSPECTION PRIOR TO ALIGNMENT
WHEELS AND TIRES
Examine the following items:
■■ The tires are inflated to the manufacturer’s specified tire pressure
■■ The steer axle tires are the same size and type
■■ The lug nuts are tightened to manufacturer’s specified torque
■■ The wheels are balanced and check for tire to rim runout
■■ The wheels and tires are free of excessive wear and damage
■■ Wheel bearing end play is within OEM specification

FRONT SUSPENSION
Inspect the following:
■■ All fasteners are installed and tightened to the specified torque. See Torque Specification

Section of this publication.

■■ Leaf springs are free of wear or damage
■■ Air springs are free of wear or damage (if equipped)
■■ Shock absorbers are free of wear and damage
■■ Vehicle ride height for both the front and rear are within specification. Follow manufacturer’s

guidelines (if equipped).

■■ Front and rear spring mounts for wear or damage

INSPECT TIE ROD ENDS
Perform the “Tie Rod Inspection” procedure, refer to the Preventive Maintenance Section of this
publication.

REAR AXLE AND REAR SUSPENSION
Rear axle misalignment can cause front tire wear. If the outer edge of one front tire is worn and
the inner edge of the other front tire is worn, check the following:
■■ Make sure the rear axle (especially a tandem axle) is correctly aligned. Refer to the procedure

from the manufacturer of the vehicle or the suspension.

Alignment & Adjustments

28

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AIRTEK® for Tiffin Motorhome Chassis
■■ All fasteners including U-bolts (if applicable) are installed and tightened to the specified torque
■■ The leaf springs are not worn or damaged
■■ The bushings in the leaf springs are not worn or damaged
■■ The torque rods (if used) are correctly adjusted (if adjustable)
■■ The frame is not bent or twisted
■■ Refer to any additional recommendations and specifications from the manufacturer of vehicle

on rear axles and suspensions. Reference the TMC (The Technology & Maintenance Council)
Guidelines for Total Vehicle Alignment.

FRONT WHEEL ALIGNMENT
Hendrickson recommends technicians review TMC’s publication TMC (Technology & Maintenance
Council) “Guidelines for Total Vehicle Alignment”.
The AIRTEK front wheel alignment specification can be found in the Front Wheel Alignment
Specification Section of this publication.
Check the total vehicle wheel alignment when the following occur:
■■ Every 80,000 to 100,000 miles (128,700 to 160,900 kms), or 12-18 months (normal main-

tenance), whichever comes first.

■■ When the vehicle does not steer correctly
■■ To correct a tire wear condition

For rear wheel alignment specifications and adjustment refer to the vehicle manufacturer.
The front wheel alignment specifications can be found in the Alignment Section of this publication. There are two types of front wheel alignment:
1. Minor alignment – a minor front wheel alignment is done for all normal maintenance conditions, see below.
2. Major alignment – a major alignment is done when uneven or excessive tire wear is evident,
or response at the steering wheel is sluggish, or the need for major wheel alignment check
and adjustment is required, see below.

MINOR FRONT WHEEL ALIGNMENT
Perform the minor front wheel alignment in the following sequence:
1. Inspect all systems that affect wheel alignment. Refer to “Inspection Prior to Alignment” in this
section.
2. Check the wheel bearing end play.
3. Check and adjust the vehicle ride height as per the vehicle manufacturer’s specifications.
4. Check toe-in and adjust if necessary.

MAJOR FRONT WHEEL ALIGNMENT
Be certain to follow wheel alignment inspection intervals as specified by the original equipment
manufacturer. Before performing a major front wheel alignment it is recommended that alignment
equipment calibration be checked to ensure proper vehicle alignment.
Major wheel alignment is accomplished in the following sequence of operation:
1. Inspect all the systems that influence the wheel alignment. Refer to the “Inspection Prior to
Alignment” in this section.
2. Check and adjust the maximum turn angle, refer to the Steering Stop Adjustment Procedure in
this section, see Figures 8-9 and 8-10.

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Alignment & Adjustments

AIRTEK® for Tiffin Motorhome Chassis
FIGURE 8-9

FIGURE 8-10

3. If the vehicle is equipped with power steering, check the pressure relief in the power steering
system and reset if necessary. Refer to vehicle manufacturer regarding the subject: Adjusting
the Pressure Relief in the Power Steering System.
4. Verify the turning angle per Step 2, (toe-out during vehicle turns or the Ackermann angle).
Refer to vehicle manufacturer’s specifications.
5. Check the kingpin (or steering axis) inclination (the kingpin inclination is not adjustable).
Refer to “Kingpin Inclination”, in the Alignment Definitions in this section.
6. Check the camber angle. DO NOT attempt to adjust. Refer to “Camber” in the Alignment
Definitions in this section.
AXLE CAMBER IS NOT ADJUSTABLE. DO NOT CHANGE THE AXLE CAMBER ANGLE OR BEND THE
AXLE BEAM. BENDING THE AXLE BEAM TO CHANGE THE CAMBER ANGLE CAN DAMAGE THE AXLE AND
REDUCE AXLE STRENGTH, AND WILL VOID HENDRICKSON’S WARRANTY. A BENT AXLE BEAM CAN
CAUSE LOSS OF VEHICLE CONTROL, POSSIBLY CAUSING PERSONAL INJURY OR PROPERTY DAMAGE,
SEE FIGURES 8-11.
UNAUTHORIZED TAMPERING OF STEERTEK NXT INTEGRATED AXLE SPRING SEATS CAN CAUSE
COMPONENT AND STRUCTURAL DAMAGE AND RESULT IN LOSS OF VEHICLE CONTROL, SEVERE
PERSONAL INJURY OR DEATH, PROPERTY DAMAGE, AND WILL VOID ANY APPLICABLE WARRANTY, SEE
FIGURE 8-11.
■■ DO NOT REMOVE, MODIFY OR REPLACE INTEGRATED AXLE SPRING SEAT OR FASTENERS.
FIGURE 8-11
®

®

NOTE

Contact Hendrickson Tech Services for any questions regarding STEERTEK NXT integrated axle
spring seats and / or fasteners.
7. Check and adjust caster angle. Refer to “Caster” in the Alignment Definitions in this section.
The use of two different angle caster shims will not change cross caster. Cross caster is the
difference between the caster readings for left and right side of the vehicle.

Alignment & Adjustments

30

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AIRTEK® for Tiffin Motorhome Chassis
SERVICE HINT

Prior to checking caster confirm that the vehicle is at its proper ride height front and rear. The front
and rear ride height must be correct to achieve proper caster.
8. Check and adjust toe-in, refer to Toe Setting in this Section.

RIDE HEIGHT VERIFICATION
NOTE

The height control valve is not supplied by Hendrickson, although it is a required component.
Hendrickson is not responsible for components supplied by the vehicle manufacturer. For assistance with inspection, maintenance and rebuild instructions of these components, refer to
vehicle manufacturer.

STEERING STOP
ADJUSTMENT PROCEDURE
When the axle or lower steering knuckle is replaced, the steering stop adjustment must
be checked.
ALWAYS CHECK / RESET THE STEERING GEAR BOX POPPET WHEN THE WHEEL CUT IS DECREASED.
FOLLOW MANUFACTURER’S GUIDELINES FOR THE GEAR BOX POPPET RESETTING PROCEDURE.
FAILURE TO DO SO CAN RESULT IN PREMATURE FAILURE OF THE AXLE OR STEERING KNUCKLE. THIS
CONDITION CAN CAUSE LOSS OF VEHICLE CONTROL, POSSIBLE PERSONAL INJURY OR PROPERTY
DAMAGE AND VOID ANY APPLICABLE WARRANTY.
FIGURE 8-12

1. Drive the vehicle on turntables and chock the rear
wheels.
2. Measure the wheel cut. The
wheel cut is determined by
steering the tires. Wheel cut
is measured at the inside
wheel only, therefore the
tires must be turned to the
full lock position for each
right hand and left hand
direction. Refer to the vehicle manufacturer for exact specifications.
3. Increase the wheel cut by loosening the jam nuts and screw the axle stops in clockwise.
4. Tighten the jam nuts.
NOTE

It is very important that the sides of the square head axle stops are set parallel to the axle beam
to ensure a good contact point on the axle, see Figure 8-12.
5. Decrease the wheel cut by loosening the jam nuts and screw the axle stops out
counter-clock‑wise.
6. Tighten the jam nuts to

50 ± 10 foot pounds torque.

7. Measure the wheel cut and check for any interference with related steering components.

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Alignment & Adjustments

AIRTEK® for Tiffin Motorhome Chassis
TOE SETTING
1. Place the vehicle on a level floor with the wheels in a straight ahead position.
2. Raise the vehicle and support the front axle with jack stands.
3. Use paint and mark the center area of tread on both steer axle tires around the complete
outer diameter of the tires.
4. Scribe a line through both steer axle tires in the painted area around the complete outer
diameter of the tires.
5. Raise the vehicle and remove the jack stands.
6. Set the vehicle on the ground.
NOTE

DO NOT measure toe-in with the front axle off the ground. The weight of the vehicle must be on the
front axle when toe-in is measured.
7. Use a trammel bar and measure the distance between the scribe marks at the rear of the
steer axle tires. Record the measurement.
8. Install the trammel bar and measure the distance between the scribe marks at the front of the
steer axle tires. Record the measurement, see Figure 8-13.

NOTE

When setting up the trammel bar the pointers should be level with the spindles at the front and
rear of the steer axle tires.
9. To calculate the toe setting subtract the front measurement from the rear measurement, the
difference between the two will equal the toe-in / toe-out measurement.
FIGURE 8-13

Trammel Bar

▲

Trammel Bar
Pointers

FRONT

Scribe Marks

10. If the toe measurement is not within the specifications of 1/16" ± 1/32" (0.060" ± 0.030"), it will
be necessary to adjust the toe setting. Refer to the following procedure.
a. Loosen the tie rod cross tube clamp bolts and locknuts.
b. Turn the tie rod cross tube until the specified toe-in distance is achieved.
c. Tighten the bolt and locknut on the tie rod cross tube to

Alignment & Adjustments

32

68 ± 7 foot pounds torque.

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AIRTEK® for Tiffin Motorhome Chassis
FIGURE 8-14
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.
5/8" Tie

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

Threaded Portion
of the Tie Rod End

THE THREADED PORTION OF THE TIE ROD END MUST EXTEND PAST THE SLOTS INTO THE TIE ROD (SEE
FIGURE 8-14) 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.

11. Verify the 5⁄8" tie rod clamp bolt head does not contact the lower shock mount at full wheel
cut, see Figure 8-14.
12. Repeat Steps 1-10 until the correct toe setting is achieved.

SPRING EYE RE-TORQUE
■■ This procedure to re-torque is necessary when replacing the: front hanger, shackle assembly

and leaf spring assembly

RE-TORQUE PROCEDURE
1. Chock the rear wheels of the vehicle to prevent movement.
2. Verify ride height. Adjust if necessary, as per the vehicle manufacturer’s specifications.
NOTE

DO NOT remove the spring eye bolts.
3. Loosen all six (6) front and rear spring eye bolts, see Figures 8-15.
FIGURE 8-15

¾" Shackle Bolt
Tightening Torque
400 ± 20 ft. lbs.
(543 ± 27 Nm)
¾" Spring Eye Bolt
Tightening Torque
400 ± 20 ft. lbs. (543 ± 27 Nm)

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Alignment & Adjustments

AIRTEK® for Tiffin Motorhome Chassis
FIGURE 8-16

4. Let the suspension settle.
5. Tighten the front ¾" spring eye bolt locknuts to 400 ± 20 foot pounds torque.
6. Tighten the rear ¾" spring eye bolt and
shackle bolt locknuts to 400 ± 20 foot
pounds torque.
7. Affix a straight edge to the bottom of the
frame rail in front of the air spring, see
Figure 8‑16.
8. With the vehicle on a level surface measure the distance from the top of the
straight edge to the ground on both
sides of the vehicle and record the
measurements.
9. Measure the difference from one side to
the other.
10. Do a road test and repeat measurement
Steps 7 to 9.
11. If the measurement is less than 3⁄8" the
vehicle is level. If measurement is more
than 3⁄8" contact Hendrickson Tech Services.

Alignment & Adjustments

34

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AIRTEK® for Tiffin Motorhome Chassis
SECTION 9

Component Replacement
FASTENERS
Hendrickson recommends that when servicing the vehicle to replace the removed fasteners with
new equivalent fasteners. Maintain correct torque values at all times. Check torque values as specified. See Hendrickson’s Torque Specifications in the Appendix of this publication. If non‑Hendrickson
fasteners are used, follow torque specifications listed in the vehicle manufacturer’s service manual.

HEIGHT CONTROL VALVE
NOTE

The height control valve is not supplied by Hendrickson, although it is a required component.
Hendrickson is not responsible for components supplied by the vehicle manufacturer. For assistance with inspection, maintenance and rebuild instructions of these components, refer to
vehicle manufacturer.

AIR SPRING
DISASSEMBLY