Lateral Cab Motion
M-852-001
(September 2007)

Valid for
All GU models

Case description
On certain CTP and GU model chassis, lateral motion of the cab may be experienced when entering, during and
exiting a turn. To dampen this lateral motion, a cab lateral damper and mounting arrangement has been developed
and is available through the MACK Parts System. Should lateral cab motion complaints be encountered, installation of
the cab lateral damper is recommended.
Note: Does not apply to Mack Trucks Australia.

Required parts
Lateral Cab Shock — GU and CTP Models

Key

Qty.

Part No.

Description

1

1

30QS5375M

Mounting bracket, cab side

2

9

271AM8

Flat washer, hardened, M8

3

5

26AM13

Bolt, flange-head, M8 x 1.25 - 25 mm long

4

4

26AM14

Bolt, flange-head, M8 x 1.25 - 30 mm long

5

4

191AM2

Flange nut, serrated, prevailing torque, M8 x
1.25

6

1

30QS4613M

Mounting bracket, frame side

7

1

13ME3246M2 Heat shield (required for dual exhaust system)

8

1

83AX698

Heat shield (required for dual exhaust system)

9

1

14QK3111

Cab lateral damper

10

1

30QS3648M

Spacer, required when fuel tank mounting Jbracket is mounted behind the vertical cab
shock absorber bracket

11

5

27AM87*

Bolt, flange-head, M14 x 2.00 x 40 mm long

5

27AM99*

Bolt, flange-head, M14 x 2.00 x 50 mm long

5

191AM5

Nut, M14 x 2.00

12

* Length of bolt depends upon component stack-up (i.e., frame rail thickness, inside
frame liner, etc.). Refer to the part number table following figure 11 to determine which
bolt must be used.

Procedures for installing the cab lateral damper are as follows:
1. Secure the chassis for service, apply the parking brakes and block the wheels to prevent the vehicle from
moving.
2. Disconnect the fuel line and the vent line from the fuel tank. Plug the lines, and also plug the ports in the tank to
prevent dirt entry.
3. Disconnect the fuel level sensor harness connector.
4. Position a suitable lifting device (such as a transmission jack with a suitable cradle) under the fuel tank.

Warning
Be sure the transmission jack is positioned under the center of the tank to keep it properly balanced
when it is being removed from the chassis. The fuel in the tank may slosh from side-to-side, resulting in
the tank falling from the jack.
5. Remove the nuts from the fuel tank mounting strap T-bolts at the bottom of the fuel tank.
6. Carefully lower the jack. Lift the mounting straps out of the way, and then roll the fuel tank away from the
chassis. Place the jack and tank in a safe location where they will not interfere with the remaining procedures,
and where the tank cannot be inadvertently knocked off the jack.
7. Installation of the cab lateral damper mounting bracket requires that three holes for the rearward mounting
fasteners be drilled in the cab floor panel. Install the cab lateral damper mounting bracket as follows:
a. Remove both the driver and rider seats.
b. Remove the trim panels from the cab back wall, and also remove the carpeting from the cab floor.
c. Clean the silicone sealant from the forward two holes in the cab floor where the cab damper mounting
bracket will be secured. It will be necessary to drill the remaining holes in the cab floor for installation of
the cab damper mounting bracket.
Note: The forward hole on the left-hand side of the cab floor already includes a weld nut for the mounting
bracket fastener, whereas the right-hand hole does not include a weld nut.
d. Using an M8 x 1.25 tap, clean the silicone sealant from the threads of the weld nut on the left-hand
side of the cab floor.
Cab Lateral Damper Mounting Bracket Drilling and Mounting Locations

e. Locate the mounting bracket (part No. 30QS5375M) in place underneath the cab floor, and secure
with one bolt (part No. 26AM13) and flat washer (part No. 271AM8) at the forward hole on the left-hand
side of the cab floor (location that includes the weld nut). Also install a bolt (part No. 26AM14), washer
(part No. 271AM8) and nut (part No. 191AM2) at the right-hand side lower cab flange.
Note: Apply never-seize compound to the threads of the bolts before installing.
Locating Damper Mounting Bracket Underneath Cab Floor

Key

Qty.

Part No.

Description

1

1

30QS5375M

Bracket, cab side, damper mounting

2

1

26AM13

Bolt, flange-head, M8 x 1.25 - 25 mm long

3

2

271AM8

Flat washer, M8

4

1

26AM14

Bolt, flange-head, M8 x 1.25 - 30 mm long

5

1

191AM2

Flange nuts, serrated, prevailing torque, M8 x 1.25

f. Using the bracket as a guide, drill the three 10 mm (3/8") holes in the cab floor for the rear mounting
bolts. Drill the holes from underneath the cab floor.
Drill Damper Bracket Mounting Holes in Cab Floor

g. Secure the mounting bracket to the floor panel using four bolts (part No. 26AM13), flat washers (part
No. 271AM8) and nuts (191AM2). Apply never-seize compound to the threads of the bolts before
installing. Hand-tighten the fasteners at this time.
Install Damper Mounting Bracket Fasteners — Cab Floor

Key

Qty.

Part No.

Description

1

4

26AM13

Bolt, flange-head, M8 x 1.25 - 25 mm long

2

4

271AM8

Flat washer, M8

3

4

191AM2

Flange nuts, serrated, prevailing torque, M8 x 1.25

h. Secure the mounting bracket to the cab back wall lower flange using three bolts (part No. 26AM14),
flat washers (part No. 271AM8) and nuts (part No. 191AM2). Apply never-seize compound to the threads
of the bolt before installing, and be sure to install the cab leveling linkage rod mounting bracket to the
left-hand side lower cab flange mounting bolt.
To prevent bending the cab lower flange, hand-tighten the bolts under the cab first, and then completely
tighten the fasteners at the cab lower flange. Once the cab lower flange nuts are tightened, completely
tighten the fasteners underneath the cab.
Install Damper Mounting Bracket Fasteners — Cab Lower Flange

Key

Qty.

Part No.

Description

1

3

26AM14

Bolt, flange-head, M8 x 1.25 - 30 mm long

2

3

271AM8

Flat washer, M8

3

3

191AM2

Flange nuts, serrated, prevailing torque, M8 x 1.25

i. Reinstall the carpeting, the cab back wall trim panel and the driver and rider seats.
8. For CTP models equipped with a dual exhaust, install the heat shield (part No. 13ME3246M2) on the exhaust
pipe using a clamp (part No. 83AX698). Position the heat shield as shown in the following illustration.
Installing Heat Shield (Chassis with Dual Exhausts Only)

Key

Qty.

Part No.

Description

1

1

13ME3246M2

Heat shield

2

1

83AX698

Clamp, size No. 60 (4.25" max. dia., 3.31" min. dia.)

9. Cut a 4" x 4" wooden block approximately 222 mm (8-3/4") long.
10. Move the cab leveling arm UP to raise the cab slightly, and then place the 4" x 4" block of wood between the
cab floor and the frame rail on the left-hand side of the cab.
11. Move the cab leveling arm DOWN to lower the cab onto the wooden block.
Block of Wood Positioned Between Frame Rail and Cab Floor

12. Completely drain the air system.
13. With the cab suspension air bag completely deflated, remove the cab vertical shock absorber from the left-hand
side of the vehicle.

Remove Cab Vertical Shock Absorber

14. Remove and discard the left-rear cab shock absorber mounting bracket from the frame rail. The bracket is
secured to the frame rail with Huck-Spin® frame fasteners. For information on removing Huck® fasteners, refer
to the Frame, Axle and Suspension Service and Total Vehicle Alignment service manual, 14-103.

Caution
If a torch is used to cut the fasteners, use caution, as there are air lines and wire harnesses routed
inside the frame rail directly behind the cab mounting bracket. The air lines and harnesses can be
damaged by the hot pins as they are being cut and removed.
15. Temporarily install the new cab shock absorber mounting bracket (part No. 30QS4613M) on the frame rail, and
then mark the location where the three additional mounting holes must be drilled.
Marking Location for Additional Mounting Holes

16. Remove the frame bracket and then drill the three 15 mm diameter mounting holes in the frame.
17. Install the cab vertical shock absorber mounting bracket (part No. 30QS4613M) to the frame. If the fuel tank
mounting bracket is located under the shock absorber mounting bracket, a spacer (part No. 30QS3648M) will
be required. The length of the bolts depends upon frame rail thickness, if equipped with an inside liner and if
the 30QS3648M spacer is required. Select the proper bolt part numbers from the chart below, and use five nuts
(part No. 191AM5) to secure the bracket to the frame rail. Tighten the fasteners to 183 N•m (135 lb-ft).
Installing Cab Vertical Shock Absorber Mounting Bracket

Key Qty.

Part No.

Description
Mounting bracket, cab vertical shock absorber

1

1

30QS4613M

2

1

30QS3648M Spacer (required if fuel tank mounting bracket is located under
the vertical shock absorber mounting bracket)

3

5

-

Refer to table below for proper part numbers

4

5

191AM5

Nut, M14 x 2.00

Bolt Part Nos.
Frame
Bracket Bracket
Rail
Only
and
Thickness
Spacer

Bracket
and
Inside
Frame
Liner

Bracket,
Spacer
and
Inside
Fame
Liner

7 mm

27AM87 27AM87 Not
Not
Applicable Applicable

8 mm

27AM87 27AM87 27AM87

27AM99

9.5 mm

27AM87 27AM87 27AM87

27AM99

11.1 mm

27AM87 27AM99 27AM99

27AM99

18. Assemble the mounting studs onto both ends of the lateral damper (part No. 14QK3111). The studs are
supplied with the damper.
Assembling Lateral Damper Mounting Studs

19. Install the lateral damper to the mounting brackets. For the damper to function properly, the rod end must be
installed on the cab mounting bracket as shown below. Install the damper with the mounting studs installed into
the brackets from the back.
Note: To facilitate installation of the damper, extend the rod from the body so that the length of the damper from
the center of the two mounting holes is approximately 18" (457 mm).
Installing Cab Lateral Damper

20. Reinstall the cab vertical shock absorber.
21. Position the fuel tank alongside the frame, and then raise the jack into position so that the mounting strap Tbolts can be installed to the J-bracket. Install new nuts (part No. 190AM4) to the T-bolts and tighten to the
following torque specification:
Steel Fuel Tanks — 61 N•m (45 lb-ft)
Aluminum Fuel Tanks — 54 N•m (40 lb-ft)
Note: Do not reuse the existing fuel tank mounting nuts. New nuts (part No. 190AM4) must be used.
Install the nuts dry. Do not lubricate the nut or T-bolt threads.
22. Reconnect the fuel line, vent line and fuel level sensor harness connector.
23. Reinstall the fasteners between the fender extension and lower step.
24. Start the engine and build air system pressure to governor cut-out.
25. When the cab air bags are fully inflated, remove the wooden block from under the cab.
26. Check cab ride height. Ride height dimension is 187 mm ± 3 mm (7.36" ± 0.12"), dimension “A” in the
illustration below. If ride height is not within specifications, adjust as follows:
Cab Ride Height Measurement

a. Loosen the linkage rod at the cab bracket.
b. Manually operate the leveling valve arm to raise or lower the rear of the cab as required to obtain the proper
ride height dimension (187 mm ± 3 mm [7.36" ± 0.12"]).

Warning
Keep hands and arms out of the way to avoid injury when performing this procedure.
c. With the cab at proper ride height, tighten the linkage rod mounting nut at the cab bracket without allowing
the leveling valve arm to move.
d. Recheck cab ride height. If not within specifications, readjust as required.

Warranty information
Reimbursement
This repair may be eligible for Reimbursement
reimbursement if a product
failure was experienced
within time and mileage limits
of the applicable Warranty
coverage. Reimbursement is
obtained via the normal claim
handling process.
Claim Type (used only when
uploading from the Dealer
Bus. Sys.)
Labour Code

W

Primary Labor Code

668 3A 00 80 –
3.5 hrs. — Time
allowed to install
cab lateral shock
absorber on
CTP and GU
models without
dual exhaust.
Does not include
“take-charge”
time.
668 3B 00 80 –
3.7 hrs. — Time
allowed to install
cab lateral shock
absorber on
CTP model
chassis with dual
exhaust. Does
not include
“take-charge”
time.

Issued by
Technical Service
Mack Trucks, Inc. engages in a continuous program of testing and evaluating to provide the best possible product.
Mack Trucks, Inc., however, is not committed to, or liable for updating existing chassis.