ULTIMAAX® Rear Suspension
for Kenworth Vehicles
SUBJECT: Service Instructions
LIT NO: 17730-301
DATE: August 2018
REVISION: C

TABLE OF CONTENTS
Section 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2

Section 7

Section 2

Product Description . . . . . . . . . . . . . . . . . 2

Drive Axle Pinion Angle . . . . . . . . . . . . . . . . 29

Section 3

Important Safety Notice. . . . . . . . . . . . . . 4

Drive Axle Alignment. . . . . . . . . . . . . . . . . . 29

Section 4

Parts List. . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Axle Lateral Alignment. . . . . . . . . . . . . . . . . 31

Section 5

Special Tools . . . . . . . . . . . . . . . . . . . . . . 12

Bar Pin Alignment. . . . . . . . . . . . . . . . . . . . 31

Section 6

Preventive Maintenance

Section 8

Hendrickson Recommended
Inspection Intervals . . . . . . . . . . . . . . . . 14

Alignment & Adjustments

Component Replacement
Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Shock Absorber – ULTIMAAX 46K•52K. . . . . 34

Component Inspection . . . . . . . . . . . . . . . . 14
Center Bushing. . . . . . . . . . . . . . . . . . . . . . 15

Shear Spring / Frame Hanger Assembly /
Saddle Assembly . . . . . . . . . . . . . . . . . . 35

Equalizing Beam End Connection. . . . . . . . 16

Progressive Load Spring (PLS). . . . . . . . . . . 40

Bar Pin Style End Bushings –
ULTIMAAX 46K•52K. . . . . . . . . . . . . . . . 20

Equalizing Beam. . . . . . . . . . . . . . . . . . . . . 41
Equalizing Beam Center Bushing. . . . . . . . . 44

Bar Pin Shims – ULTIMAAX 46K•52K. . . . . . 20

Bar Pin Style End Bushings –
ULTIMAAX 46K•52K. . . . . . . . . . . . . . . . 47

Beam End Axle Brackets . . . . . . . . . . . . . . . 20
Frame Hanger Assembly . . . . . . . . . . . . . . . 21

Adapter Style End Bushing –
ULTIMAAX 60K•70K. . . . . . . . . . . . . . . . 49

Shear Springs. . . . . . . . . . . . . . . . . . . . . . . 22

Cross Tube. . . . . . . . . . . . . . . . . . . . . . . . . . 52

Progressive Load Springs (PLS). . . . . . . . . . 23

Torque Rods . . . . . . . . . . . . . . . . . . . . . . . . 54

Saddle Connection. . . . . . . . . . . . . . . . . . . 24

XTRB Torque Rod Bushings . . . . . . . . . . . . . 56

Cross Tube. . . . . . . . . . . . . . . . . . . . . . . . . . 25
Torque Rods . . . . . . . . . . . . . . . . . . . . . . . . 26

Section 9

Torque Specifications. . . . . . . . . . . . . . . 58

Shock Absorbers (if equipped) . . . . . . . . . . 26

Section 10 Troubleshooting Guide. . . . . . . . . . . . . . 62

ULTIMAAX® for Kenworth Vehicles
SECTION 1

Introduction
This publication is intended to acquaint and assist maintenance personnel in the preventive
maintenance, service, and repair of the ULTIMAAX® Rear Rubber Suspension System for applicable
Kenworth Vehicles.
NOTE

Use only Hendrickson Genuine parts for servicing this suspension system.
It is important to read and understand the entire Technical Procedure publication prior to
­performing any maintenance, service, or repair of this product. The information in this publication contains parts lists, safety information, product specifications, features, proper maintenance,
service, and repair instructions for ULTIMAAX ­suspensions.
Hendrickson reserves the right to make changes and improvements to its products and
­publications at any time. Contact Hendrickson Tech Services for information on the latest version
of this manual at 1-866-755-5968 (toll-free U.S. and Canada), 1-630-910-2800 (outside U.S. and
Canada) or e-mail: techservices@hendrickson‑intl.com.
The latest revision of this publication is available online at www.hendrickson-intl.com.

SECTION 2

Product Description
ULTIMAAX is an advanced severe-duty rear rubber suspension designed to balance outstanding
durability, empty ride quality, loaded stability and mobility. Through its unique design, the system
offers premium ride quality in both empty and loaded conditions, with increasing stability as the
load increases. The ULTIMAAX system is capable of extremely high articulation for demanding jobsite or off-highway conditions. When loaded, it delivers up to 17.5" of diagonal wheel articulation.
■■ Equalizing beam — Formed and robotically welded to provide a narrow profile for weight

savings. Distributes load equally between axles to improve maneuverability, stability and
handling. Increases ground clearance with flat bottom design. Lowers the center of gravity to
increase stability.

■■ Frame hangers — Optimized design to balance durability and weight savings. Fabricated to

offer flexibility with multiple truck configurations.

■■ Premium rubber bushings — Require no lubrication. Extend service life and reduce re-bush

time with rugged bar pin axle connection. Improve articulation with high performance patent
pending design.

■■ Progressive load springs — Designed to balance empty ride quality and loaded stability.

Stiffness of progressive load spring increases as load increases, providing a unique balance
of empty ride quality and loaded stability.

■■ Rubber shear springs — Primary springs in unloaded condition, providing superb ride quality.

React to longitudinal loads during braking and accelerating for minimal displacement.

■■ Saddle — Triangular geometry provides structure and durability. Weight efficient design

helps to increase payload, while offering a considerable weight savings versus competitive
suspensions.

■■ Torque rods — Longitudinal torque rods are engineered to optimize resistance to axle wind-

up during acceleration and braking. Transverse torque rods ensure maximum lateral axle
control and straight line suspension stability. V-rods are engineered to evenly distribute higher
capacity longitudinal and lateral loads into the chassis connections.

Introduction

2

17730-301

ULTIMAAX® for Kenworth Vehicles
FIGURE 2-1

46K • 52K Capacity

60K • 70K Capacity

ULTIMAAX® SPECIFICATIONS
46K

52K

60K

70K

Suspension Rating

46,000 lbs.

52,000 lbs.

60,000 lbs.

70,000 lbs.

Suspension Weight1

1,179 lbs.

1,198 lbs.

1,407 lbs.

1,750 lbs.

GVW Approval
GCW Approval
Site Travel Rating

Contact Vehicle Manufacturer

Contact Vehicle Manufacturer

Contact Vehicle Manufacturer

Contact Vehicle Manufacturer

70,000 lbs.

2

Diagonal Articulation

3

Lift Axles

75,000 lbs.
17.5 in.

80,000 lbs.

90,000 lbs.
17.5"

Approved

Approved

Ride Heights

9.5 – 13 in.

9.5 – 13 in.

Axle Spacing4

52, 54, 56, 60 in.

56, 60 in.

Hendrickson approves the use of ULTIMAAX in the following vocational truck applications: dump, concrete mixer, refuse, logging, crane /
boom, platform and fire / rescue. All such applications must comply with applicable Hendrickson specifications and must also be approved
by the respective vehicle manufacturer with the vehicle in its original, as-built configuration. Contact Hendrickson and the respective vehicle
manufacturer for approval of additional applications.
1. Installed weight includes full suspensions with torque rods and without shocks.
2. Site travel rating – operators using vehicles equipped with liftable pusher or tag axles must not exceed published ratings. Ratings are
limited to no more than five percent of vehicle operation at speed not to exceed five mph. Liftable pusher or tag axles should only be raised
(or unloaded) to improve vehicle maneuverability in off-road use or when vehicle is empty. Site travel ratings are consistent with published
axle manufacturer’s limitations. Axle and suspension site travel specifications must not be exceeded.
3. Suspension articulation may exceed vehicle’s capability and may be limited by vehicle manufacturer; vehicle manufacturer installed axle
stops may restrict suspension’s articulation.
4. Contact Hendrickson for availability of additional beam lengths.
Actual product performance may vary depending upon vehicle configuration, operation, service and other factors.
U.S. and foreign patents granted and / or pending.

17730-301

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Product Description

ULTIMAAX® for Kenworth Vehicles
SECTION 3

Important Safety Notice
Proper maintenance, service and repair are important to the reliable operation of the suspension.
The procedures recommended by Hendrickson and described in this technical publication are
methods of performing such maintenance, service and repair.
This technical publication should be read carefully to help prevent personal injury and to assure
that proper methods are used. Improper maintenance, service or repair may damage the vehicle,
cause personal injury, render the vehicle unsafe in operation, or void the manufacturer's warranty.
Failure to follow the safety precautions in this manual can result in personal injury and/or property
damage. Carefully read and understand all safety related information within this publication, on
all decals and in all such materials provided by the vehicle manufacturer before conducting any
maintenance, service or repair.
■■

EXPLANATION OF SIGNAL WORDS

Hazard “Signal Words” (Danger • Warning • Caution) appear in various locations throughout this
publication. Information accented by one of these signal words must be observed to help minimize the risk of personal injury to service personnel, or possibility of improper service methods
which may damage the vehicle or render it unsafe.
This is the safety alert symbol. It is used to alert you to potential personal injury hazards. Obey all safety messages that follow this symbol to avoid possible injury or death.
Additional Notes or Service Hints are utilized to emphasize areas of procedural importance and provide suggestions for ease of repair. The following definitions indicate the use of
these signal words as they appear throughout the publication.
INDICATES AN IMMINENTLY HAZARDOUS SITUATION, WHICH IF NOT AVOIDED, WILL RESULT IN SERIOUS
INJURY OR DEATH.
INDICATES A POTENTIAL HAZARDOUS SITUATION WHICH, IF NOT AVOIDED, CAN RESULT IN SERIOUS
INJURY OR DEATH.
INDICATES A POTENTIAL HAZARDOUS SITUATION WHICH, IF NOT AVOIDED, MAY RESULT IN MINOR OR
MODERATE INJURY.

NOTE

An operating procedure, practice condition, etc. which is essential to emphasize.

SERVICE HINT

A helpful suggestion that will make the service being performed a little easier and/or faster.
Also note that particular service operations may require the use of special tools designed for specific
purposes.These special tools can be found in the “Special Tools” Section of this publication.
The torque symbol alerts you to tighten the fasteners to a specific torque value. See Torque
Specifications Section of this publication.

Important Safety Notice

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ULTIMAAX® for Kenworth Vehicles
■■

SAFETY PRECAUTIONS

FASTENERS
DISCARD USED FASTENERS. ALWAYS USE NEW FASTENERS TO COMPLETE A REPAIR. FAILURE TO DO
SO COULD RESULT IN FAILURE OF THE PART, OR MATING COMPONENTS, ADVERSE VEHICLE HANDLING,
PERSONAL INJURY, OR PROPERTY DAMAGE.
LOOSE OR OVER TORQUED FASTENERS CAN CAUSE COMPONENT DAMAGE, ADVERSE VEHICLE
HANDLING, PROPERTY DAMAGE, OR SEVERE PERSONAL INJURY. MAINTAIN CORRECT TORQUE VALUE
AT ALL TIMES. CHECK TORQUE VALUES ON A REGULAR BASIS AS SPECIFIED, USING A REGULARLY
CALIBRATED TORQUE WRENCH. TORQUE VALUES SPECIFIED IN THIS TECHNICAL PUBLICATION ARE FOR
HENDRICKSON SUPPLIED FASTENERS ONLY. IF NON-HENDRICKSON FASTENERS ARE USED, FOLLOW
TORQUE SPECIFICATION LISTED IN THE VEHICLE MANUFACTURER’S SERVICE MANUAL.
TORCH/WELDING
DO NOT USE A CUTTING TORCH TO REMOVE ANY FASTENERS OR BUSHINGS. THE USE OF HEAT
ON SUSPENSION COMPONENTS WILL ADVERSELY AFFECT THE STRENGTH OF THESE PARTS. A
COMPONENT DAMAGED IN THIS MANNER CAN RESULT IN THE ADVERSE VEHICLE HANDLING AND
POSSIBLE PERSONAL INJURY OR PROPERTY DAMAGE.
EXERCISE EXTREME CARE WHEN HANDLING OR PERFORMING MAINTENANCE IN THE AREA OF THE
EQUALIZING BEAM. DO NOT CONNECT ARC WELDING GROUND LINE TO THE EQUALIZING BEAM. DO
NOT STRIKE AN ARC WITH THE ELECTRODE ON THE EQUALIZING BEAM AND AXLE. DO NOT USE HEAT
NEAR THE EQUALIZING BEAM ASSEMBLY. DO NOT NICK OR GOUGE THE EQUALIZING BEAM. SUCH
IMPROPER ACTIONS CAN DAMAGE THE EQUALIZING BEAM ASSEMBLY AND CAUSE ADVERSE VEHICLE
HANDLING AND POSSIBLE PERSONAL INJURY OR PROPERTY DAMAGE.
LOAD CAPACITY
ADHERE TO THE PUBLISHED CAPACITY RATINGS FOR THE SUSPENSION. ADD-ON AXLE ATTACHMENTS
AND OTHER LOAD TRANSFERRING DEVICES CAN INCREASE THE SUSPENSION LOAD ABOVE ITS RATED
AND APPROVED CAPACITIES, WHICH CAN RESULT IN COMPONENT DAMAGE AND ADVERSE VEHICLE
HANDLING, POSSIBLY CAUSING PERSONAL INJURY OR PROPERTY DAMAGE.
MODIFYING COMPONENTS
DO NOT MODIFY OR REWORK PARTS WITHOUT AUTHORIZATION FROM HENDRICKSON. DO NOT
USE SUBSTITUTE OR REPLACEMENT COMPONENTS NOT AUTHORIZED BY HENDRICKSON. USE OF
MODIFIED, REWORKED, SUBSTITUTE OR REPLACEMENT PARTS NOT AUTHORIZED BY HENDRICKSON
MAY NOT MEET HENDRICKSON’S SPECIFICATIONS, AND CAN RESULT IN FAILURE OF THE PART,
ADVERSE VEHICLE HANDLING, AND POSSIBLE PERSONAL INJURY OR PROPERTY DAMAGE AND WILL
VOID WARRANTY. USE ONLY HENDRICKSON AUTHORIZED REPLACEMENT PARTS.
PERSONAL PROTECTIVE EQUIPMENT
ALWAYS WEAR PROPER EYE PROTECTION AND OTHER REQUIRED PERSONAL PROTECTIVE EQUIPMENT
TO HELP PREVENT PERSONAL INJURY WHEN PERFORMING VEHICLE MAINTENANCE, REPAIR OR
SERVICE.
PROCEDURES AND TOOLS
A TECHNICIAN USING A SERVICE PROCEDURE OR TOOL WHICH HAS NOT BEEN RECOMMENDED BY
HENDRICKSON MUST FIRST SATISFY HIMSELF THAT NEITHER HIS SAFETY NOR THE VEHICLE'S SAFETY
WILL BE JEOPARDIZED BY THE METHOD OR TOOL SELECTED. INDIVIDUALS DEVIATING IN ANY MANNER
FROM THE INSTRUCTIONS PROVIDED WILL ASSUME ALL RISKS OF CONSEQUENTIAL PERSONAL INJURY
OR DAMAGE TO EQUIPMENT INVOLVED.

17730-301

5

Important Safety Notice

ULTIMAAX® for Kenworth Vehicles
SUPPORT THE VEHICLE PRIOR TO SERVICING
PLACE THE VEHICLE ON A LEVEL FLOOR AND CHOCK THE WHEELS TO PREVENT THE VEHICLE FROM
MOVING OR ROLLING. DO NOT WORK AROUND OR UNDER A RAISED VEHICLE SUPPORTED BY ONLY
A FLOOR JACK OR OTHER LIFTING DEVICE. ALWAYS SUPPORT A RAISED VEHICLE WITH RIGID SAFETY
STANDS. FAILURE TO DO SO CAN CAUSE SERIOUS PERSONAL INJURY OR DAMAGE TO EQUIPMENT.
IMPROPER JACKING METHOD
IMPROPER JACKING METHODS CAN CAUSE STRUCTURAL DAMAGE WHICH CAN CAUSE ADVERSE
VEHICLE HANDLING, PROPERTY DAMAGE OR SEVERE PERSONAL INJURY AND WILL VOID
HENDRICKSON’S WARRANTY.
■■ DO NOT USE THE SUSPENSION CROSS TUBE AS A JACKING POINT, SEE FIGURE 3-1, REFER TO

VEHICLE MANUFACTURER FOR PROPER JACKING INSTRUCTIONS.

■■ ACCEPTABLE LIFTING POINTS FOR A VEHICLE AT THE RATED LOAD INCLUDE BUT ARE NOT

LIMITED TO: THE AXLE, EQUALIZING BEAM, AND THE VEHICLE FRAME RAIL. REFER TO THE VEHICLE
MANUFACTURER FOR PROPER JACKING INSTRUCTIONS.

FIGURE 3-1
ULTIMAAX 52K Shown

Center Bushing
DO NOT grease
Equalizing Beam

Cross Tube
DO NOT grease or use
as a jacking point

SADDLE CONNECTION
A SADDLE ASSEMBLY IS ATTACHED TO THE CENTER BUSHING OF EACH EQUALIZING BEAM WITH TWO (2)
SADDLE CAPS. EACH SADDLE CAP USES TWO (2) BOLTS TO CLAMP THE CENTER BUSHING INNER METAL
TO THE SADDLE. EACH SADDLE CAP MUST BE INSTALLED SO THAT THERE IS AN EVEN GAP BETWEEN THE
SADDLE CAP AND THE BASE OF THE SADDLE LEGS AS SHOWN IN FIGURE 3-2. IF EACH SADDLE CAP IS
NOT INSTALLED EVENLY, THE SADDLE LEGS COULD BECOME DEFORMED, RESULTING IN BENT BOLTS
OR DAMAGED SADDLES.
FIGURE 3-2

Saddle

Saddle Cap Locknut
M16,Tightening Torque M20,Tightening Torque
558 ± 32 ft. lbs.
200 ± 20 ft. lbs.
(757 ± 43 Nm)
(270 ± 30 Nm)

Maintain an
even gap
between
the saddle and
the saddle cap
Equalizing
Beam
Saddle Cap

Important Safety Notice

Center Bushing

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ULTIMAAX® for Kenworth Vehicles
TORQUE ROD ASSEMBLY
THE ULTIMAAX SUSPENSION INCORPORATES LONGITUDINAL,TRANSVERSE TORQUE RODS AND V-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.
PARTS CLEANING
SOLVENT CLEANERS CAN BE FLAMMABLE, POISONOUS, AND CAUSE BURNS. TO HELP AVOID SERIOUS
PERSONAL INJURY, CAREFULLY FOLLOW THE MANUFACTURER’S PRODUCT INSTRUCTIONS AND
GUIDELINES AND THE FOLLOWING PROCEDURES:
1.

WEAR PROPER EYE PROTECTION.

2.

WEAR CLOTHING THAT PROTECTS YOUR SKIN.

3.

WORK IN A WELL-VENTILATED AREA.

4.

DO NOT USE GASOLINE OR SOLVENTS THAT CONTAIN GASOLINE. GASOLINE CAN EXPLODE.

5.

HOT SOLUTION TANKS OR ALKALINE SOLUTIONS MUST BE USED CORRECTLY. FOLLOW THE
MANUFACTURER’S RECOMMENDED INSTRUCTIONS AND GUIDELINES CAREFULLY TO HELP
PREVENT PERSONAL ACCIDENT OR INJURY.

DO NOT USE HOT SOLUTION TANKS OR WATER AND ALKALINE SOLUTIONS TO CLEAN GROUND OR
POLISHED PARTS. DOING SO WILL CAUSE DAMAGE TO THE PARTS AND VOID WARRANTY.

17730-301

7

Important Safety Notice

ULTIMAAX® for Kenworth Vehicles
SECTION 4

Parts List
29
29

■■

46K • 52K CAPACITY

28

26

25

25

27

29

29

28

12

28

11
27

26

28
12

20
19

9

11

14

16

10

20
19

14
15

13

13
22
22
23
24
2
21

8

1

3

21
7