torque rod at the straddle mount end. Shims can be installed between the transverse torque
rod and the transverse torque rod frame bracket or between the transverse torque rod and
axle tower bracket. Refer to vehicle manufacturer for proper shim location; also see Lateral
Alignment in the Alignment & Adjustments Section of this publication.

■■ The transverse torque rods also control axle walk-out during cornering. The mounting brackets

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

Transverse and longitudinal torque
rods have attaching ends designated as “straddle mount,” or “tapered
stud” as shown in Figure 6-26. Most
can be replaced by pressing out the
worn torque rod bushing and installing a replacement bushing, others
require complete torque rod assembly
replacement.

Tapered Stud

Length

Straddle Mount

It is important that the tightening
torque of the nuts be checked during preventive maintenance service. Follow the vehicle manufacturer’s specifications for tightening torque values.
The tapered stud torque rod locknuts also should be checked. Refer to the Torque Specification
Section of this publication for proper torque values.

Preventive Maintenance

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ULTIMAAX® for Fire and Rescue Vehicles
SHOCK ABSORBERS
NOTE

FIGURE 6-27

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.

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 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 r­ eference, 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
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.
FIGURE 6-28

SHOCK ABSORBER VISUAL INSPECTION - UNACCEPTABLE CONDITIONS

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Preventive Maintenance

ULTIMAAX® for Fire and Rescue Vehicles
LEAKING VS. MISTING SHOCK VISUAL INSPECTION
FIGURE 6-29

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 ­operating 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.
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

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ULTIMAAX® for Fire and Rescue 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 are controlled by the torque rods.
■■ Ride height is controlled by the design of the suspension frame hanger. No adjustment is

possible.

DRIVE AXLE PINION ANGLE
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.

TO CHECK THE PINION ANGLE
FIGURE 7-1

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 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 Fire and Rescue 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

28

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ULTIMAAX® for Fire and Rescue Vehicles
AXLE LATERAL ALIGNMENT
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.

BAR PIN ALIGNMENT

FIGURE 7-4

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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Alignment & Adjustments

ULTIMAAX® for Fire and Rescue 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 7-1.

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 INBOARD AND ONE 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

30

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ULTIMAAX® for Fire and Rescue Vehicles
FIGURE 7-6

Nominal

3/16"

Axle Moves

Axle
Bracket

Axle
Bracket

Equalizing
Beam
Center

Axle Moves

Axle
Bracket

Equalizing
Beam
Center

Bar
Pin

3/16"

(4.8 mm)

Equalizing
Beam
Center

Bar
Pin

3/16"

(4.8 mm)
Alignment
Shim

Alignment
Shim
3/8"

Bar
Pin

3/8"

(9.5 mm)

(9.5 mm)

(4.8 mm)

Alignment
Shim
3/8"

(9.5 mm)

FIGURE 7-7

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 Fire and Rescue Vehicles
SECTION 8

Component Replacement
FASTENERS
When servicing an ULTIMAAX suspension, Hendrickson recommends replacing all 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.
NOTE

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

SHOCK ABSORBER
NOTE

It is not necessary to replace shock absorbers in pairs if one shock absorber requires replacement.

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 fasteners from the upper shock bracket and remove shock absorber.
FIGURE 8-1

ULTIMAAX 63K Shown

Upper
Shock Bracket

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

Equalizing Beam
with Shock Bracket
Shock Absorber
Retaining Washer
and Bushing

5/8" Locknut
Tightening Torque
80 ± 10 ft. lbs. (109 ± 14 Nm)

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

32

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ULTIMAAX® for Fire and Rescue Vehicles
SHEAR SPRING / FRAME HANGER ASSEMBLY / SADDLE ASSEMBLY
You will need:
■■

Saddle Disassembly Tool No. 66086-113L and Saddle Assembly Tool No. 66086‑108L,
refer to the Special Tools Section of this publication.
FIGURE 8-2

DISASSEMBLY
1. Chock the front wheels of the vehicle.
2. Raise and support the drive axles.
3. Remove the drive tires from the side of the
vehicle being serviced.
4. Remove and discard the M16 saddle cap
fasteners that attach the saddle assembly to
the center bushing, see Figure 8‑2.

M16 Saddle Cap
Fasteners

Center
Bushing
Saddle Cap

Saddle

5. Raise the vehicle’s frame just enough to create a ½" (13 mm) gap between the saddle assembly and center bushing. Support the vehicle’s frame at this height.
6. Remove the progressive load springs M10 fasteners and discard, see Figure 8-4.
7. Remove the progressive load springs.
8. Apply NLGI #2–EP (Extreme Pressure) chassis lubricant to the threaded rod of the saddle
disassembly tool, Part No. 66086-113L, see Figure 8-3.
FIGURE 8-3
Saddle Disassembly Tool
Hendrickson Part No.66086-113L

Threaded
Rod Nut

NOTE

FIGURE 8-4

Blocking
Nuts
Apply NLGI #2–EP
(Extreme Pressure) chassis lubricant

The threaded rod spacer and spacer nut are designed and orientated to fit into the saddle assembly openings, see Figure 8-5.
9. Install both saddle disassembly tools on each end of one saddle assembly, rotate the threaded
rod blocking nuts until each are oriented properly into the saddle assembly openings, see
Figures 8-4 and 8-5.
FIGURE 8-5

Saddle Assembly
Opening

Threaded Rod
Blocking Nuts

17730-299

Saddle Disassembly Tool
Hendrickson Part No. 66086-113L

33

Component Replacement

ULTIMAAX® for Fire and Rescue Vehicles
SERVICE HINT

Use a rachet strap attached to each saddle half and the frame or vehicle body to secure the
saddle halves during removal.
10. Snug the saddle disassembly tool.

NOTE

The shear springs are in each frame hanger are compressed when installed.
11. Remove and discard the M20 saddle fasteners, see Figure 8-6.
12. To separate the two saddle halves, evenly rotate the threaded rod nut to tighten the saddle
disassembly tool, see Figure 8-6.