The most common conditions of concern are:

17730-313

■■

Overall Fast Wear (Miles per 32nd)

■■

Feather Wear

■■

Cupping

■■

Diagonal Wear

■■

Rapid Shoulder Wear (One Shoulder Only)

■■

One-Sided Wear
23

Preventive Maintenance

AIRTEK® for Hoist Liftruck T-Series
FIGURE 7-20

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 — 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.
FIGURE 7-22

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

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:

Preventive Maintenance

■■

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.

24

17730-313

AIRTEK® for Hoist Liftruck T-Series
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.

WHEEL BEARING END PLAY
This inspection can be made with or without the wheel assembly on the vehicle.
NOTE

The correct specification to allow the wheel to rotate freely is 0.001" to 0.005" end play.
FIGURE 7-26

1. Verify end play with a dial
indicator, see Figure 7-26.
Wheel end play is the free
movement of the wheel
assembly along the spindle axis.
a. Attach a dial indicator
with its magnetic base
to the hub.
b. Adjust the dial indicator so that its plunger
or pointer is against
the end of the spindle
with its line of action
parallel to the axis of
the spindle.

17730-313

25

Preventive Maintenance

AIRTEK® for Hoist Liftruck T-Series
c. Grasp the hub assembly at the 3 o’clock and 9 o’clock positions. Push the hub in and
out while oscillating it to seat the bearings. Read bearing end play as the total indicator
movement.
NOTE

If end play is not within specification, a wheel bearing adjustment is required, refer to the vehicle
manufacturer for proper preventive maintenance and rebuild instructions.

SURFACE PAINT WEAR
AIRTEK Rear Shackle Plate — Hendrickson AIRTEK suspension system equipped on Hoist Liftruck
T-Series Vehicles, utilize 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.
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 7-27. 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.
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 7-28.
FIGURE 7-27

Preventive Maintenance

FIGURE 7-28

26

17730-313

AIRTEK® for Hoist Liftruck T-Series
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.

17730-313

27

Alignment & Adjustments

AIRTEK® for Hoist Liftruck T-Series
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

Alignment & Adjustments

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.

28

17730-313

AIRTEK® for Hoist Liftruck T-Series
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 Specifications
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.

17730-313

29

Alignment & Adjustments

AIRTEK® for Hoist Liftruck T-Series
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.

■■

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 25,000 miles (40,000 km) as necessary

■■

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 (2) 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 specified in this section.
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.
Alignment & Adjustments

30

17730-313

AIRTEK® for Hoist Liftruck T-Series
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.
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.
■■

NOTE

DO NOT REMOVE, MODIFY OR REPLACE INTEGRATED AXLE SPRING SEAT OR FASTENERS

Contact Hendrickson Tech Services for any questions regarding STEERTEK NXT integrated axle
spring seats and / or fasteners.
FIGURE 8-11

17730-313

31

Alignment & Adjustments

AIRTEK® for Hoist Liftruck T-Series
7. Check and adjust caster angle. Refer to “Caster” in the Alignment Definitions in this section.
The use of two (2) 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.
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.

DUAL HCV VERIFICATION
The recommendation of the vehicle manufacturer is that dual height control valves are only to
be installed on the front suspension when the rear suspension is equipped with a single height
control valve system. This arrangement is best suited to keep the vehicle level versus having dual
height control systems on both the front and rear suspensions.
1. Drive the vehicle onto a level surface.
2. Free and center all suspension joints by slowly moving vehicle back and forth several times
without using the brakes. It is important when coming to a complete stop to verify that the
brakes are released.
3. Chock drive wheels.
4. Verify that the air system is at full operating pressure.
NOTE

Hendrickson recommends the following be performed during any type of ride height adjustment
to help prevent socket head cap screws from loosening from the height control valve housing, and
any subsequent air leaks from the height control valve.
5. Prior to adjusting the height control valve, clean the threads of the ¼" valve mounting fasteners to remove any debris and corrosion.
6. See additional Air Spring Cautions and Warnings in the Important Safety Notice Section of this
publication prior to inflating or deflating the suspension system.

SERVICE HINT

It is very important that the leveling valve be cycled completely before and after any ride height adjustments.This cycling of the leveling valve will help to make the adjustment as accurate as possible.
7. Detach the lower rubber grommet of the height control valve linkage from the lower stud and