Preventive Maintenance

ULTIMAAX® for Kenworth Vehicles
TORQUE RODS
THE ULTIMAAX SUSPENSION INCORPORATES TORQUE RODS FOR VEHICLE STABILITY. IF THESE
COMPONENTS ARE DISCONNECTED OR ARE NON-FUNCTIONAL THE VEHICLE SHOULD NOT BE
OPERATED. FAILURE TO DO SO CAN RESULT IN ADVERSE VEHICLE HANDLING AND POSSIBLE TIRE
CONTACT WITH THE FRAME OR THE SUSPENSION.

VISUAL INSPECTION
All transverse, longitudinal or V-rods (as applicable) need to be inspected during preventive maintenance and service for looseness.
Visually inspect (1) torque rod bushings for any torn or shredded rubber material interfaces
or elongated oval shapes and (2) torque rods for any metal to metal contact, bent, cracked or
broken components. The torque rod and / or the torque rod bushings will require replacement if
any of these conditions are encountered.
Torque rod looseness inspection is necessary. With the vehicle shut down, a lever check can be
made with a long pry bar (36") placed under each torque rod end and pressure applied.
Torque rod length is determined by the original vehicle manufacturer (see Figure 6-26). The
mounting bracket at the axle housing end of the torque rods are furnished and welded into position on the axle housings by the axle or vehicle manufacturer,
FIGURE 6-26

ULTIMAAX 46K • 52K

ULTIMAAX 60K • 70K

Length

Tapered Stud

Straddle Mount
Corner
Bracket

NOTE

V-rod
Assembly

Axle Apex
Bracket

Hendrickson Suspension recommends Grade 8 bolts, hardened flat washer and Grade C locknuts
be used for all straddle mount torque rod attachments.
■■ It is important that the tightening torque of the locknuts be checked during preventive main-

tenance and service. Follow the tightening torque specifications and all applicable preventive
maintenance, service and safety instructions issued by the respective vehicle and suspension
manufacturers.

SHOCK ABSORBERS (if equipped)
NOTE

It is not necessary to replace shock absorbers in pairs if one shock absorber requires replacement.
Hendrickson offers a long service life, premium shock absorber for use on ULTIMAAX suspensions.
If shock absorber replacement is necessary, Hendrickson recommends that original Hendrickson
shock absorbers be replaced with identical Hendrickson Genuine parts for servicing. Failure to do
so will affect the suspension performance, durability, and will void the ­warranty.
Inspection of the shock absorber can be performed by doing a heat test, and a visual inspection. For instructions on shock absorber replacement see the Component Replacement Section
of this publication.

Preventive Maintenance

26

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ULTIMAAX® for Kenworth Vehicles
FIGURE 6-27

HEAT TEST
1. Drive the vehicle at moderate speeds on rough
road for minimum of fifteen minutes.
DO NOT GRAB THE SHOCK 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 body
below the dust cover. Touch the frame to get an
ambient r­eference, see Figure 6-27. 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. Listen for the sound of metal
parts rattling inside. Rattling of metal parts can indicate that the shock has an internal failure.

VISUAL INSPECTION
FIGURE 6-28

Look for any of the potential problems shown in Figure 6-28 when doing a visual inspection.
Inspect the shock absorbers fully extended. Replace as necessary.
SHOCK ABSORBER VISUAL INSPECTION - UNACCEPTABLE CONDITIONS

FIGURE 6-29

LEAKING VS. MISTING VISUAL INSPECTION
The inspection must not be conducted after driving
in wet weather or a vehicle wash. Shocks need to be
free from water. Many shocks are often misdiagnosed
as failures. Misting is the process whereby very small
amounts of shock fluid evaporate at a high o­ perating
temperature through the upper seal of the shock,
see Figure 6-29. When the “mist” reaches the cooler
outside air, it condenses and forms a film on the outside of the shock body. Misting is perfectly normal
and necessary function of the shock. The fluid, which
evaporates through the seal area helps to lubricate
and prolong the life of the seal.

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27

Preventive Maintenance

ULTIMAAX® for Kenworth Vehicles
A shock that is truly leaking and needs to be replaced will show signs of fluid leaking in streams
from the upper seal. These streams can easily be seen when the shock is fully extended, underneath the main body (dust cover) of the shock. Look for these potential problems when doing a
visual inspection. Inspect the shock absorbers fully extended. Replace as necessary.
NOTE

The ULTIMAAX suspension is equipped with a premium seal on the shock, however this seal will allow
for misting to appear on the shock body (misting is not a leak and is considered acceptable).
If the shock is damaged, install new shock absorber and replace as detailed in the Component
Replacement Section of this publication.

Preventive Maintenance

28

17730-301

ULTIMAAX® for Kenworth Vehicles
SECTION 7

Alignment & Adjustments
AXLE ALIGNMENT
■■ The primary control for axle alignment is the location of the frame hanger assemblies on

the frame rail as installed by the vehicle manufacturer, and the location of the axle brackets
on the axles as installed by the axle or vehicle manufacturer.

■■ Axle centering and pinion angles for (1) ULTIMAAX 46K • 52K are controlled by the longitu-

dinal and transverse torque rods, and (2) ULTIMAAX 60K • 70K are controlled by the V-rods. All
such torque rods are not adjustable.

■■ Ride height is controlled by the design of the suspension frame hanger. No adjustment is possible.

DRIVE AXLE PINION ANGLE
NOTE

Drive axle pinion angle for vehicles equipped with V-rods is non-adjustable.
Drive axle pinion angles are established by the vehicle manufacturer. If pinion angle adjustment
is required, check for proper angles with the vehicle manufacturer. Pinion angle is set by the longitudinal torque rod length.
FIGURE 7-1

TO CHECK THE PINION ANGLE
1. Use a work bay with a level floor.
2. Relax the suspension by slowly
moving the vehicle back and forth
several times in a straight line
without using the brakes. This will
slacken or loosen the suspension
as the vehicle is positioned. End
with all wheels positioned straight
ahead. Roll to a stop without the brakes being applied. DO NOT set the parking brake.
3. Chock the front wheels of the vehicle.
4. Place a digital protractor on the axle housing as shown in Figure 7-1.
5. Check to see if the pinion angle is correct per the vehicle manufacturer’s specified range.
6. If necessary, add/remove shims at the longitudinal torque rod connections as required to
achieve the proper pinion angle.
7. When the pinion angle is correct tighten all fasteners to the proper torque specifications per
the vehicle manufacturer and recheck the pinion angles.
8. Remove wheel chocks.

DRIVE AXLE ALIGNMENT
NOTE

Drive axle alignment with suspensions equipped with adapter style equalizing beam end connections ARE NOT adjustable.
Computerized alignment equipment is the preferred method of measuring alignment. To calculate
the shim thickness required, the target offset must be converted to thrust angle, see alignment
equipment manufacturer for procedures. If, however, computerized axle alignment equipment is
not available refer to the following Inspection in this section.

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Alignment & Adjustments

ULTIMAAX® for Kenworth Vehicles
Proper alignment is essential for maximum ride quality, performance, and tire service life. The following recommended alignment procedure as described below, should be performed if excessive
or irregular tire wear is observed.
NOTE

Proper vehicle alignment can only be achieved when all axles are aligned to the vehicle’s centerline and the steering axle’s caster, camber and toe-in settings are within specifications.

FIGURE 7-2

▲

INSPECTION

FRONT

1. Use a work bay with a level, flat surface.
2. Relax the suspension by slowly moving the vehicle back and forth several
times in a straight line. This will slacken or loosen the suspension as the
vehicle is positioned. End with all wheels positioned straight ahead.
3. DO NOT set the parking brake. Chock the front wheels of the vehicle.
B
4. Verify the vehicle system air is at full operating pressure.
5. Verify all suspension components are in good condition. Repair or replace
any worn or damaged suspension components before proceeding with the
alignment process.
D
6. Ensure all drive axle tires are at the same size.
7. Securely clamp a six-foot piece of STRAIGHT bar stock or angle iron across
the lower frame flange as shown in Figure 7-2. Select a location for the bar
stock or angle iron as far forward of the drive axle as possible where compoTrammel
nents will not interfere.
Bar
8. Accurately square the bar stock or angle iron to the frame using a carpenter’s square.
9. Using a measuring tape, measure from the straight edge to the forward face of the front drive
axle arms on both sides of the vehicle as shown in Figure 7-2, dimensions A and B.
10. Calculate the difference between measurements A and B.
a. If the front drive axle is within vehicle manufacturer’s specifications, proceed to check the
rear drive axle (Step 11).
b. If alignment of the front drive axle IS NOT within the vehicle manufacturer’s specifications,
then the alignment of this axle MUST be corrected BEFORE measuring the rear drive axle
alignment (Step 11).
c. If the suspension is equipped with bar pin end bushings, correct the alignment of this axle
by following the bar pin alignment instructions in this section.

A

C

NOTE

Since the remaining drive axle will be aligned relative to the front drive axle, it is essential that the
front drive axle is aligned within the vehicle manufacturer’s specifications prior to the alignment
of the remaining drive axle.
11. Using a trammel bar, measure the distance from the spindle center of the front drive axle to the
spindle center of the rear drive axle on both sides of the vehicle; see Figure 7-2, C and D.
12. Calculate the difference between measurements C and D.
a. If the measurements are within the vehicle manufacturer’s specifications, then the rear
drive axle alignment is acceptable.
b. If alignment of the rear drive axle IS NOT within the vehicle manufacturer’s specifications,
then the alignment of this axle MUST be corrected.
c. If the suspension is equipped with bar pin end bushings, correct the alignment of this axle
by following the Bar Pin with Shims Alignment instructions in this section.
13. Recheck measurements to confirm adjustments. Repeat Steps 10 through 12 until the correct
alignment is achieved.
14. After all drive axles are aligned, check the pinion angle of each drive, refer to the Axle Pinon
Angle in this section.

Alignment & Adjustments

30

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ULTIMAAX® for Kenworth Vehicles
AXLE LATERAL ALIGNMENT
NOTE

Axle lateral alignment for vehicles equipped with V-rods is non-adjustable.
1. Use a work bay with a level floor.
2. Drive the vehicle slowly, straight ahead. Try to slacken or loosen the suspension as the vehicle
is positioned. End with all wheels positioned straight ahead. Try to roll to a stop without the
brakes being used. DO NOT set the parking brake.
3. Chock the front wheels of the vehicle.
4. Measure from the outside of the frame rail to the rim flange of the inner tire. Record the measurement A and B, see Figure 7-3.

FIGURE 7-3

▲

5. Measure the same distance on the opposite side of the same axle. Record the measurement
C and D, see Figure 7-3.

FRONT
A

C

B

D

6. Verify the axle lateral alignment is within the vehicle manufacturer’s specifications. Adding
or removing shims that are located between the transverse torque rod and the frame rail will
normally correct the axle lateral alignment.
■■

A general rule of thumb is to use a torque rod shim with a thickness that is half of the difference between the two measurements.

EXAMPLE

If the axle lateral alignment is out of specification by ¼" (6 mm), remove or install a 1⁄8" (3 mm)
torque rod shim between the transverse torque rod and frame rail as needed. Refer to Longitudinal
and Transverse Torque Rod Section in Preventive Maintenance Section of this publication.

NOTE

Hendrickson recommends the use of Grade 8 bolts and Grade C locknuts. Washers are not necessary when flanged fasteners are used.
FIGURE 7-4
ULTIMAAX
46K • 52K Shown

BAR PIN ALIGNMENT
The alignment feature consists of specially designed, tightly tolerance steel
shims which fill the 3⁄8" (9.5 mm) total
gap between the bushing’s bar pin and
the axle bracket legs. The gap must
be filled by placing the shims on the
bushing assembly in one of the positions shown in Figure 7-4. Hendrickson
has three shim designs options for
alignment, part number 50130-000
(provided), 50131-000 and 57026‑000,
see Figure 7-7.

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31

Axle Bracket
Supplied by
Manufacturer

1" Locknut
Tightening Torque
525 ± 75 ft. lbs
(712 ± 102 Nm)

Bar Pin

Bar Pin
Shim
1" Bolt,Tightening Torque
575 ± 75 ft. lbs (780 ± 102 Nm)

Alignment & Adjustments

ULTIMAAX® for Kenworth Vehicles
A BAR PIN SHIM MUST BE INSTALLED AT EACH BOLT LOCATION. THE SAME PART NUMBER SHIM IN THE
SAME ORIENTATION MUST BE USED AT BOTH BOLT LOCATIONS ON ANY ONE END BUSHING. DO NOT
INSTALL OR STACK MORE THAN ONE SHIM AT EACH BOLT LOCATION. USE GENUINE HENDRICKSON BAR
PIN SHIMS, DO NOT USE STANDARD WASHERS. FAILURE TO FOLLOW THESE WARNINGS MAY RESULT IN
IMPROPER VEHICLE ALIGNMENT, FRACTURE OF THE AXLE BRACKET OR BAR PIN WHICH COULD RESULT IN
THE ADVERSE VEHICLE HANDLING AND POSSIBLE PERSONAL INJURY OR PROPERTY DAMAGE.

ALIGNMENT ADJUSTMENT
FIGURE 7-5

If alignment of the drive axles is required, as determined by an
alignment inspection procedure, the following steps will need
to be performed.
1. Determine direction of axle thrust angle. Figure 7-5 illustrates the forward drive axle with a thrust angle to the left
(-negative thrust).
SERVICE HINT

Axle movement is in the same direction as the increased shim
thickness, see Figure 7-6.
2. To determine where to adjust shim thickness use measurement A and B for front drive axle or C and D for rear drive
axle, see Figure 7-2.

SERVICE HINT

Axle adjustment will be on the side of the bar pin where shim
thickness is increased. For example, to correct the axle thrust
angle illustrated in Figure 7-5, shim thickness will need to be
increased at the front of the bar pin (Location X) and/or the
rear of the bar pin (Location Y).

NOTE

Computerized alignment equipment is the preferred method of measuring alignment. To calculate
the shim thickness required the target offset must be converted to thrust angle, see alignment
equipment manufacturer for procedures.
3. Chock the wheels of the front axles to prevent vehicle movement during service.
4. Raise the frame of the vehicle to remove the load from the suspension. Support the frame at
this height.
5. Support the equalizing beam and remove the fasteners from the end bushing where the bar
pin alignment shim adjustment is being made.
6. Adjust shim thickness to move the axle in the desired direction, see Figure 7-6.
EACH EQUALIZING BEAM END BUSHING HAS ONE (1) INBOARD AND ONE (1) OUTBOARD ALIGNMENT
SHIM, FOR A TOTAL OF FOUR SETS OF TWO ALIGNMENT SHIMS PER SUSPENSION. EACH SET OF
ALIGNMENT SHIMS FOR A PARTICULAR BEAM END BUSHING MUST BE INSTALLED IN THE SAME
ORIENTATION. SHIM ORIENTATION MAY DIFFER FOR EACH BEAM END BUSHING, SEE FIGURE 7-4. FAILURE
TO FOLLOW THESE WARNINGS MAY RESULT IN THE FRACTURE OF EITHER THE AXLE BRACKET OR BAR
PIN WHICH COULD RESULT IN THE ADVERSE VEHICLE HANDLING AND POSSIBLE PERSONAL INJURY OR
PROPERTY DAMAGE.
THE BAR PIN ALIGNMENT SHIM (PART NO. 50130-000) MUST BE INSTALLED WITH THE FOLDED
EDGE FACING AWAY FROM THE BUSHING, SEE FIGURE 7-7. FAILURE TO DO SO MAY RESULT IN
SHIM DAMAGE, IMPROPER ALIGNMENT, DAMAGE OR FRACTURE OF THE AXLE BRACKET OR BAR PIN
WHICH COULD RESULT IN THE ADVERSE VEHICLE HANDLING AND POSSIBLE PERSONAL INJURY OR
PROPERTY DAMAGE.

7. Install new end bushing fasteners and tighten to:
■■ At the locknut to
525 ± 75 foot pounds torque, or
■■ At the bolt head to
575 ± 75 foot pounds torque
Alignment & Adjustments

32

17730-301

ULTIMAAX® for Kenworth Vehicles
FIGURE 7-6

FIGURE 7-7

BAR PIN ALIGNMENT SHIMS
The following service notes will help when performing Hendrickson equalizing beam bar pin alignment

The standard alignment shims supplied with each
suspension (P/N 50130-000) have two 3/16" (4.8 mm) legs
and a 3/8" (9.5 mm) back. Rotating the shim pairs 90° will
change the axle alignment in ± 3/16" (4.8 mm) increments.
If a finer adjustment is required use alignment shim (P/N
50131-000).This alignment shim has one 1/8" (3.2 mm) leg,
one ¼" (6.4 mm) leg, and a 3/8" (9.5 mm) back. A total of ¾"
(19 mm) adjustment is achievable to the axle. A 3/8" (9.5 mm)
flat shim is also available (P/N 57026-000).
Part Number
50130-000

1/8
3/16

Part Number
50131-000

Part Number
57026-000

3/8"

(1.5 mm) shim thickness increases thrust angle
by 0.10".
To accomplish a thrust angle adjustment rotate the
alignment shims on the bar pin of the end bushing.
Axle movement will be in the direction of the shim
thickness increase.
Axle thrust angle may be adjusted at either wheel end
on an axle. If insufficient adjustment is available at
one wheel end, the opposing wheel end will also
need to be adjusted, but in the opposite direction.

Example: The alignment equipment shows the front drive
axle to have a 0.40° thrust angle to the left.This will
require a ¼" (6.4 mm) shim thickness increase to the
front side of the left front equalizing beam end bushing. If
there is less than ¼" (6.4 mm) of adjustment available at
this location then some of the adjustment will have to be
made at the rear of the right front end bushing. In this
case a 1/8" (3.2 mm) shim thickness increase at the front
side of the left front bar pin AND a 1/8" (3.2 mm) shim
thickness increase at the rear side of the right front bar
pin will correct the 0.40° thrust angle.

" (3.2 mm) Leg

" (4.8 mm) Legs ¼" (6.4 mm) Leg

1/16"

(9.5 mm) Leg

NOTE: Folded edge in 50130-000 shim
must be positioned away from the bushing

8. Remove support and lower the vehicle.
9. Verify the axles’ alignments are within the vehicle manufactures tolerance.
10. Set brakes and remove wheel chocks.

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Alignment & Adjustments

ULTIMAAX® for Kenworth Vehicles
SECTION 8

Component Replacement
FASTENERS
When servicing an ULTIMAAX suspension, Hendrickson recommends replacing all removed fasteners with new genuine Hendrickson 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.
NOTE

Torque values shown in this publication apply only if Hendrickson supplied fasteners are used. If
non Hendrickson fasteners are used, follow the torque specification listed in the vehicle manufacturer’s service manual.

SHOCK ABSORBER – ULTIMAAX 46K•52K
NOTE

It is not necessary to replace shock absorbers in pairs if one shock absorber requires replacement.
FIGURE 8-1
ULTIMAAX 46K • 52K Shown

Upper Shock Bracket

M16 Upper Shock Bracket Fasteners
Tightening Torque
170 ± 20 ft. lbs. (231 ± 27 Nm)

Shock Absorber

Equalizing Beam
with Shock Bracket

Retaining Washer
and Bushing

5/8" Locknut
Tightening Torque
80 ± 10 ft. lbs. (109 ± 19 Nm)

DISASSEMBLY
1. Chock the front wheels of the vehicle.
2. Remove the lower shock absorber nylon locknut, retainer washer and rubber bushing from the
shock absorber stud, see Figure 8-1.
3. Remove the upper shock fasteners from the upper shock bracket, see Figure 8-1.
4. Remove shock absorber.

ASSEMBLY
1. Mount the shock absorber in the upper shock bracket and install fasteners, tighten to
170 ± 20 foot pounds torque, see Figure 8-1.
2. Locate the shock absorber stud in the lower shock bracket and install the rubber bushing,
retainer washer and nylon locknut. Tighten to 80 ± 10 foot pounds torque, see Figure 8-1.
3. Remove the wheel chocks.

Component Replacement

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ULTIMAAX® for Kenworth Vehicles
SHEAR SPRING / FRAME HANGER ASSEMBLY / SADDLE ASSEMBLY
You will need:
■■ Saddle Disassembly Tool Part No. 66086-113L and Saddle Assembly Tool Part No.

66086‑108L, refer to the Special Tools Section of this publication.

FIGURE 8-2

DISASSEMBLY
1. Chock the front wheels of the vehicle.

M16 or M20