■■ Vehicle – Diagnose mechanical problem and correct.

17730-311

21

Preventive Maintenance

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
Figure 7-21

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.
Figure 7-22

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.
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 Inspection
Refer to Meritor for wheel bearing end play inspection and wheel bearing adjustment procedures.

Preventive Maintenance

22

17730-311

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles

SECTION 8

Alignment & Adjustments
Alignment Definitions
Figure 8-1

Ackermann steering geometry — The geometry of the four bar
linkage consisting of the front axle, two knuckle assemblies, and tie
rod assembly is designed to provide free rolling of front tire 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 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

17730-311

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 returnability. 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.

23

Alignment & Adjustments

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
Figure 8-4

Kingpin inclination (KPI) — The inward tilt of the kingpin from the vertical. This front
suspension parameter has a pronounced effect on steering effort and returnability. 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.

Figure 8-5

Figure 8-7

Figure 8-6

Scrub, skew, tram angle or parallelism
— The angle formed by two thrust or
tracking lines of a tandem (or multiple)
axle vehicle. As indicated by the term
“parallelism”, the ideal condition is
when the two thrust lines form a 0°
angle, or are parallel to each other.
Positive skew or tram is when the
distance between the right axle ends is
less than the distance between the left.
Any scrub angle other than 0° will cause
the tandem axles to work against each
other. The steer axle must be turned to
offset the “push” of the tandem axles to
keep the vehicle moving straight ahead.
This causes every tire on the vehicle to “scrub”. Tire wear from tandem scrubbing occurs at
the leading edge of the steer tires in a pattern called “inside / outside” wear, that is, the inside
edge of the left steer tire and the outside edge of the right steer tire will exhibit irregular wear
for example. Additional tire wear may occur on all tandem axle tires.
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.”

Alignment & Adjustments

24

17730-311

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
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 8-8

Figure 8-9

Figure 8-10

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.
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.
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 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.

17730-311

25

Alignment & Adjustments

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
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.
■■ 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 sec-

tion of this publication.

■■ Leaf springs are free of wear or damage.
■■ Shock absorbers are free of wear and damage.
■■ Vehicle ride height for both the front and rear are within specification. Follow m
­ anufacturer’s

guidelines (if equipped).

■■ Front and rear spring mounts are free of wear or damage.

Inspect Tie Rod Ends
Perform Tie Rod Inspection procedure; refer to the Preventive Maintenance section of this
publication.

Rear Axle and Rear Suspension
The rear axle 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

dictated by the vehicle or suspension manufacturer.

■■ 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 Technology & Maintenance Council (TMC)
Guidelines for Total Vehicle Alignment.

Front Wheel Alignment
Hendrickson recommends technicians review The Technology & Maintenance Council’s publication (TMC) “Guidelines for Total Vehicle Alignment” (TMC RP 642).
Check total (front and rear) vehicle wheel alignment when any of the following occurs:
■■ Every 80,000 to 100,000 miles, or 12-18 months (normal maintenance).
■■ When the vehicle does not steer correctly.
■■ To correct a tire wear condition.
Alignment & Adjustments

26

17730-311

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
For rear wheel alignment specifications and adjustments refer to the vehicle manufacturer.
The front wheel alignment specifications can be found in the Alignment Specifications 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 the Inspection Prior to Alignment in
this section.
2. Check the wheel bearing end play.
3. Check and adjust toe.
4. Check and adjust the vehicle ride height as specified in the Preventive Maintenance section
of this publication.

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 8-11 and 8-12.
Figure 8-11

Figure 8-12

3. If the vehicle is equipped with power steering, check the pressure relief in the power steering system and reset if necessary. Refer to the vehicle manufacturer regarding the subject:
Adjusting the Pressure Relief in the Power Steering System.
4. Check the turning angle. Refer to the original equipment manufacturer specifications.
5. Check the kingpin (or steering axis) inclination. Refer to Kingpin Inclination under 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 figure 8-13.

17730-311

27

Alignment & Adjustments

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
Figure 8-13

6. Check camber angle. Do not attempt to adjust camber. Refer to “Camber” under the
Alignment Definitions in this section.
7. It is necessary to verify that all ride heights (front and rear) are within specifications prior to
checking caster to get an accurate caster reading.
8. Check and adjust caster angle. Refer to Caster Angle under Alignment Definitions in this section.
NOTE

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.
9. Check and adjust toe-in, refer to “Toe Setting” in this section.

Steering Stop
Figure 8-14

Adjustment Procedure
When the axle or steering
knuckle is replaced, the steering stop adjustment must
be checked.
Ensure the sides
of square head
axle stops are
set parallel to
the axle beam

The steering stop adjustment
procedure is as follows:
1. Drive truck onto 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 8-14.
5. Decrease the wheel cut by loosening the jam nuts and screw the axle stops out
counter-clockwise.
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.
Alignment & Adjustments

28

17730-311

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
Always check / reset the steering gear box poppets 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, personal injury or property damage and
void any applicable warranty.

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 8-15.
Figure 8-15

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.
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.

17730-311

29

Alignment & Adjustments

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
b. Turn the tie rod cross tube until the specified toe-in distance is achieved.
The threaded portion of the tie rod end must extend past the slots into the tie rod
cross tube, see Figure 8-16. Failure TO DO SO CAN CAUSE COMPONENT TO FAIL CAUSING LOSS
OF VEHICLE CONTROL AND POSSIBLE PERSONAL INJURY OR PROPERTY DAMAGE.

c. Tighten the bolt and locknut on the tie rod cross tube to

68 ± 7 foot pounds torque.

Figure 8-16
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.

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 8-16.
12. Repeat Steps 1-10 until the correct toe setting is achieved.

Alignment & Adjustments

30

17730-311

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles

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 section of this publication. If non-Hendrickson
fasteners are used follow torque specifications listed in the vehicle manufacturer’s service manual.

Shock Absorber
It is not necessary to replace the shock absorber in pairs if only one shock absorber requires
­replacement.

Disassembly
1. Place the vehicle on a level floor.
2. Chock the wheels.
3. Remove the lower mounting bolts, fasteners, and spacer.
4. Remove the upper mounting bolts and fasteners.
5. Slide out the shock absorber.
6. Inspect the shock absorber mounting brackets and hardware for damage or wear, replace as
necessary.
Figure 9-1

Assembly
1. Install the upper inboard shock spacer, shock absorber and fasteners into the upper shock
absorber bracket, see Figure 9-1. Snug fasteners, DO NOT tighten at this time.
2. Install the lower bolt from the outboard side of the leaf spring shock mount and attach the
washer, outboard spacer, inboard spacer and locknut, see Figure 9-1.
3. Tighten the upper and lower shock eye locknuts to

188 ± 13 foot pounds torque.

4. Remove the wheel chocks.

17730-311

31

Component Replacement

STEERTEK NXT High Capacity Steer Axle System for Fire and Rescue Vehicles
Front Leaf Spring Frame Hanger
Disassembly
1. Place the vehicle on level floor.
2. Chock the wheels.
3. Raise the frame and support the vehicle with frame stands.
4. Support the front axle with a floor jack.
5. Remove the lower shock absorber mounting fasteners.
SERVICE HINT

A floor jack may be required to support the axle.
6. Loosen or remove the bottom cap fasteners from the opposite side frame hanger / spring pin
connection.
7. Remove the bottom cap and fasteners from the hanger being replaced, see Figure 9-2.
8. Lower the floor jack until the spring eye / spring pin clears the front frame hanger legs.
9. Remove the frame mounting fasteners from the hanger per manufacturer’s guidelines.
10. Remove the hanger from the vehicle.
Figure 9-2

Assembly
½" Locknut
Tightening Torque
80 ± 8 ft. lbs.

1. Install the new hanger on the frame.
2. Install new frame fasteners per manufacturer’s guidelines.
3. Raise the axle into the front hanger.
4. Install the front hanger bottom cap and
fasteners.
5. Tighten the ½" locknut to
pounds torque.

80 ± 8 foot

6. Install the lower shock absorber mounting
fasteners to
188 ± 13 foot pounds
torque..
7. Remove the frame stands and lower frame.

Front
Frame Hanger

Leaf Spring
Assembly

Front Hanger
Bottom Cap

½" Washer

8. Remove the wheel chocks.