SERVICE BULLETIN

Number: SB313002
Date: 12/21/07
Model: CXN, CHN,
CT, CX, CH,
CV, CL
(Also applies to Mack Trucks Australia)
(Supersedes SB313002 dated 11/09/06)

Air-Operated Clutch Assist System — Adjustment,

Troubleshooting and Retrofit Instructions
This service bulletin provides a description of the air-operated clutch assist arrangement
which is available on certain MACK model chassis equipped with either a MACK or vendor
transmission. Also included is retrofit instructions, part numbers, adjustment procedures and
a troubleshooting guide.
With the air operated clutch assist, clutch pedal effort is reduced by approximately 20%,
along with 2″ (50.8 mm) less pedal travel. The reduction in clutch pedal travel results in
reduced initial pedal height, providing more leg and knee room for the operator. This system
increases operator comfort by reducing leg strain.
The air-operated clutch assist consists of a clutch cable with an integral pressure regulator
and a single-acting air cylinder. All components are made from corrosion resistant materials
for added performance, durability and reliability.
1

Figure 1 — Air-Operated Clutch Assist Arrangement

SB313002 — Page 1 of 21
SERVICE PUBLICATIONS, ALLENTOWN, PA 18105 ©MACK TRUCKS, INC. 2007
Key Qty. Part No. Description
1 1 63AX3877 Y-Fitting
2 1 27RC47M Cable assembly, clutch, CXN, CHN, CX and CH without REPTO, CV
with REPTO, CT with or without REPTO
1 27RC47M2 Cable assembly, clutch, CV without REPTO
1 27RC47M3 Cable assembly, clutch, CL without REPTO
3 1 63AX3981 Filter, air cylinder exhaust port
4 1 63AX51438R Fitting, push-to-connect connector, 1/4" tube, internal 1/8" NPTF

5 6 48RU2313 Tie wraps

6 108" 101AX120RF Tube, air line, 1/4", total length, 108" (2 743 mm), 38" (96.5 mm) for
supply-to-pressure regulator line, 8" (20.3 mm) for pressure
regulator-to-cylinder delivery line and 62" (1 574.8 mm) for cylinder
exhaust port-to-remote mounted cylinder
7 1 26QB433M Bracket, mounting, CXN, CHN, CT, CX, CV, CH and CL (with MACK
engine) models all without REPTO
1 26QB434M Bracket, mounting, CT, CX, CV, CH and CL (with MACK engine)
models all with REPTO
1 26QB54M Bracket, mounting, CL model with Cummins engine (requires three
nuts [part No. 191AM2] to mount the bracket to the oil pan mounting
studs)
8 1 84AX549 Threaded rod end, male
9 2 21AX317 Lock nut, 7/16-20UNF
10 1 20AX4 Nut, 7/16-20UNF
11 2 63AX54124 Fitting, 90-degree elbow, push-to-connect connector, 1/4" tube,
external 1/8" NPTF
12 1 36MX31BM Cylinder, clutch assist

13 1 8MY428 Boot, assist cylinder rod

14 1 84AX548 Threaded rod end, female
15 1 33MX43M Lever, clutch release
16 1 35AX634 Spacer
17 1 1AX189 Bolt, 5/16-24UNF-2A x 2-1/2” long
18 1 37AX68 Flat washer 11/32” ID
19 1 21AX314 Lock nut, 5/16-24UNF
20 1 33MX315 Clutch dog, MACK transmissions
1 33MX316 Clutch dog, Eaton® Fuller® transmissions
21 2 77AM16 Pan head Torx® screw, M6 x 1.0 x 20 mm long

22 2 154AM5001 Lock nut (with nylon insert), M6 x 1.0

23 2 30AM12 Cap screw, flange-head, with patch lock, M12 x 1.75 x 30 mm long
— 1 12AX154 Rubber stop, clutch pedal (not shown on exploded view)

SB313002 — Page 2 of 21
Individual components for the clutch cable assemblies are available separately through the
MACK Parts System. Part numbers are as follows:
2

Figure 2 — Clutch Cable Components

Cable Assembly
Part No. Key Qty. Part No. Description
27RC47M 1 1 2894-195300001 Replacement cable
2 1 2894-190300237 Regulator
3 1 2894-195300040 Kit, hardware (includes one threaded rod
end, two 90-degree push-to-connect air
fittings, one spring and two nuts)

27RC47M2 1 1 2894-195300002 Replacement cable

2 1 2894-190300237 Regulator
3 1 2894-195300040 Kit, hardware (includes one threaded rod
end, two 90-degree push-to-connect air
fittings, one spring and two nuts)

27RC47M3 1 1 2894-195300003 Replacement cable

2 1 2894-190300237 Regulator
3 1 2894-195300040 Kit, hardware (includes one threaded rod
end, two 90-degree push-to-connect air
fittings, one spring and two nuts)

27RC48M 1 1 2894-195300023 Replacement Cable

2 1 2894-190300239 Regulator
3 1 2894-195300040 Kit, hardware (includes one threaded rod
end, two 90-degree push-to-connect air
fittings, one spring and two nuts)

SB313002 — Page 3 of 21
Pressure for the clutch assist is supplied from the pressure protection valve located on the
treadle valve. As the clutch pedal is pushed in to disengage the clutch, movement of the
clutch cable opens the pressure regulator to allow air flow to the rod end of the cylinder. The
amount of force placed on the clutch cable determines how much pressure is delivered by
the regulator. As pressure enters the cylinder, the cylinder rod retracts and pulls the clutch
release lever. The action of the assist cylinder pulling the release lever reduces the amount
of pedal effort required to disengage the clutch.
3

Figure 3 — Air-Operated Clutch Assist Air Flow Diagram (Disengaging Clutch)

SB313002 — Page 4 of 21
When the clutch pedal is released to engage the clutch, the pressure regulator closes and
shuts off the flow of air to the cylinder. The return spring (integral with the clutch cable
assembly) returns the release lever to its home position, and the returning release lever
pulls the rod from the cylinder. As the rod extends, pressure inside the cylinder exhausts
through an exhaust port in the regulator valve.
4

Figure 4 — Air-Operated Clutch Assist Air Flow Diagram (Engaging Clutch)

Clutch Pedal Stop
The air-operated clutch assist arrangement requires a thicker pedal stop on the pedal
mounting bracket. The same rubber stop (part No. 12AX154) fits both the standard clutch
pedal with rubber pedal pad and open grate clutch pedal arrangements.
5

Figure 5 — Clutch Pedal Rubber Stop

SB313002 — Page 5 of 21
Clutch Release Cylinder Exhaust Filter

As the clutch pedal is pushed in to disengage the clutch, the assist cylinder rod retracts into
the cylinder. Air trapped in the “head-end” of the cylinder exhausts through the exhaust port
at the rear of the cylinder. When the clutch pedal is released to engage the clutch, the
cylinder rod extends. As the rod extends, air is drawn back into the cylinder through the
exhaust port. The exhaust port includes a sintered-bronze filter (part No. 63AX3981) to
prevent contaminants from entering the cylinder. A clogged filter can result in a “spongy”
clutch pedal or an increase in pedal effort. Should either of these conditions be noticed,
remove the filter from the cylinder, clean in a suitable non-flammable solvent, blow dry with
shop air and reinstall.

Clutch Adjustment Procedures

When installing or replacing a clutch cable, the threaded end of

the cable must not protrude into the clevis at the pedal end of the
cable. DO NOT make any adjustments to the clutch cable in an
attempt to compensate for clutch linkage wear.
6

Figure 6 — Clevis at Pedal End of Clutch Cable

In order for the clutch to release properly, the clutch release bearing must travel between
1/2″–9/16″ (12.7–14.3 mm), and there must be 1/8″ (3.2 mm) of clearance between the
clutch release yoke and the release bearing wear pads. The 1/8" (3.2 mm) of clearance
between the clutch release yoke and the release bearing wear pads equates to 1-1/8" of
clutch pedal free travel in the cab.

With the clutch properly adjusted, clutch brake squeeze should occur within the last 1/4" to
3/8" (6.35 to 9.53 mm) of pedal travel.

SB313002 — Page 6 of 21
Clutch adjustment procedures are as follows:
Verify and Adjust Clutch Brake Squeeze
Verify that clutch brake squeeze occurs within the last 1/4" to 3/8" (6.35 to 9.53 mm) of
clutch pedal travel. Clutch brake squeeze is verified as follows:
7

Figure 7 — Verify Clutch Brake Squeeze

1. Remove the inspection cover from the transmission bell housing.
2. Insert a 0.010" (0.254 mm) thickness gauge between the rear face of the clutch release
bearing and the clutch brake.
3. Have an assistant fully depress the clutch pedal and then slowly release the pedal. Tell
the assistant to stop releasing the pedal as soon as the thickness gauge can be pulled
from between the release bearing and the clutch brake.
4. Measure to see if the pedal is within the last 1/4" to 3/8" (6.35 to 9.53 mm) of travel. If
clutch brake squeeze does not occur within the last 1/4" to 3/8" (6.35 to 9.53 mm) of
pedal travel, adjust as follows:
8

Figure 8 — Clutch Brake Squeeze Adjustment

SB313002 — Page 7 of 21
 a. Loosen the clutch dog lock bolt.
b. Loosen the adjusting bolt jam nut.
c. Turn the adjusting bolt to properly set clutch brake squeeze.
앫 Turning the adjusting bolt clockwise results in clutch brake squeeze occurring
further from the end of pedal travel (increases dimension).
앫 Turning the adjusting bolt counterclockwise results in clutch brake squeeze
occurring closer to the end of pedal travel (decreases dimension).
d. When clutch brake squeeze has been properly set, tighten the clutch dog bolt and
the adjusting bolt jam nut.

Adjust Clutch Pedal Free Play

After verifying and adjusting clutch brake squeeze as required, clutch pedal free play must
be adjusted. Clutch pedal free play for the cable-operated air-assist clutch release system
should be 1-1/8" ± 1/4" (28.6 ± 6.4 mm). With this free play dimension, there should be
approximately 3" to 3.8" (76.2 to 96.5 mm) of cylinder rod visible when measured from the
cylinder body to the bottom of the cylinder rod end. This dimension provides proper cable
travel and ensures that the cylinder will not bottom when the clutch pedal is pushed in
(clutch disengaged).
9

Figure 9 — Clutch Pedal Free Play

Clutch pedal free play is adjusted by adjusting the internal clutch ring. Adjustments for the
different model clutches are as follows:
Spicer Solo™ 15-1/2 Inch Self-Adjusting Clutch
Adjust the Spicer Solo™ 15-1/2" self-adjusting clutch by fully pressing and releasing the
clutch pedal a minimum of five times. This “release bearing to clutch brake contact” ensures
that the clutch is properly adjusted, and that release bearing travel is properly set to the
specified 1/2" to 9/16" (12.7 to 14.3 mm).

SB313002 — Page 8 of 21
Spicer Easy Pedal 15-1/2 Inch Angle Spring Clutches with Kwik-Adjust™ Component
1. Rotate the engine in the direction of normal rotation until the Kwik-Adjust™ component
is visible through the bell housing inspection hole.
2. Insert a 5/8" socket of box wrench through the inspection hole and over the hex-head
bolt on the Kwik-Adjust™ Component.
10

Figure 10 — Box Wrench Installed on Kwik-Adjust™ Component

On some clutches, the Kwik-Adjust™ component may utilize a

square-head bolt which requires a 3/4" 12-point wrench or
socket.

3. Have an assistant fully depress the clutch pedal (clutch released).

4. Depress and turn the Kwik-Adjust™ bolt in the direction of the arrow embossed on the
clutch.

The clutch must be released before attempting to turn the

adjusting component.
11

Figure 11 — Adjusting Clutch Ring

앫 Turning the Kwik-Adjust™ component clockwise moves the release bearing
toward the transmission (increases clutch pedal free play)
앫 Turning the Kwik-Adjust™ component counterclockwise moves the release
bearing toward the engine (decreases clutch pedal free play)
SB313002 — Page 9 of 21
 The Kwik-Adjust ™ component will re-engage at each sixth turn, and a flat of the hex-
head bolt will align with the flat on the edge of the bracket. Kwik-Adjust™ components
that utilize the 3/4" square-headed bolt will re-engage at every 1/4 turn.
5. Measure clutch pedal free play in the cab. If not within specifications, readjust the
clutch ring as required.
ArvinMeritor™ 15-1/2 Inch Clutch
1. Rotate the engine in the direction of normal rotation until the clutch adjusting lock plate
is visible through the bell housing inspection hole.
12

Figure 12 — Clutch Adjustment Lock Plate

2. Remove the screw and washer from the lock plate, and then remove the lock plate.
3. Have an assistant fully depress the clutch pedal (clutch released).

SB313002 — Page 10 of 21
 4. Using a universal clutch adjusting tool (tool No. J 36216) or a large screwdriver against
the notches on the adjusting ring, turn the adjusting ring to move the release bearing
as required to adjust clutch pedal free play. Moving the adjusting ring one notch moves
the release bearing approximately 0.020" (0.50 mm).

The clutch must be released before attempting to turn the clutch

adjusting ring.
13

Figure 13 — Adjusting Clutch

5. Measure clutch pedal free play in the cab. If not within specifications, readjust the
clutch ring as required.
6. Once clutch pedal free play has been adjusted to proper specifications, reinstall the
lock plate and tighten the capscrew to 27 lb-ft (37 N•m).

SB313002 — Page 11 of 21
Verify Clutch Release Yoke and Release Bearing Travel

After clutch brake squeeze and clutch pedal free play have been properly adjusted, verify
that 1/8" (3.2 mm) of clearance exists between the clutch release yoke and the release
bearing wear pads. Also verify that the release bearing travel is between 1/2" and 9/16"
(12.7 and 14.3 mm). Release bearing travel is the distance between the rear face of the
release bearing and the clutch brake. If not within specifications, recheck clutch brake
squeeze and clutch pedal free play adjustments.
14

Figure 14 — Verify Clutch Release Yoke Free Travel and Release Bearing Travel

When satisfied that the clutch is properly adjusted, reinstall the cover over the transmission
bell housing inspection hole.

Retrofitting an Air-Operated Clutch Assist System

The air-operated clutch assist system can be retrofit on a chassis having a standard cable-
operated clutch release system. Installation procedures are as follows:
1. Secure the chassis for service, apply the parking brakes and block the wheels to
prevent the vehicle from moving.
2. Completely drain the air system.
3. On chassis equipped with a manually adjusted clutch, check and adjust clutch as
outlined in this service bulletin under the heading “CLUTCH ADJUSTMENT
PROCEDURES.”
4. Remove the existing clutch release cable, cable anchor bracket, clutch dog, lever and
the clutch linkage return spring (transmission side).
5. Remove the existing rubber stop located on the clutch pedal bracket, then install the
new larger stop (part No. 12AX154).

SB313002 — Page 12 of 21
 6. Install the new cable mounting bracket to the flywheel housing (refer to the illustration
and chart below for the correct mounting bracket part number).
15

Figure 15 — Install Cable Mounting Bracket

Key Qty. Part No. Description

1 1 26QB433M Mounting bracket, clutch cable/assist cylinder, CX, CV and CH
models without REPTO, and CL with MACK engine without REPTO
1 26QB434M Mounting bracket, clutch cable/assist cylinder, CX, CV and CH
models with REPTO, and CL with MACK engine with REPTO
1 26QB54M Mounting bracket, clutch cable/assist cylinder, CL models with
Cummins ISX engine
2 2 30AM12 Screw, flange-head, with patch lock, M12 x 1.75 x 30 mm long
3 3 191AM2 Flange nut, prevailing torque, serrated, M8 x 1.25

On CL models equipped with Cummins ISX engines, the

mounting bracket is secured to three oil pan mounting studs.

7. Slide the new clutch release lever (part No. 33MX43M) onto the clutch shaft.
SB313002 — Page 13 of 21
 8. Install a nut (part No. 20AX4) onto the male threaded rod end (part No. 84AX549), and
then install the rod end on the head-end of the assist cylinder. Be sure to thread the rod
end all the way into the cylinder. Tighten the jam nut to secure the rod end in place.
9. Slide the boot (part No. 8MY428) over the cylinder rod.
10. Install a nut (part No. 20AX4) onto the cylinder rod, and then install the female
threaded rod end (part No. 84AX548) on the cylinder rod. Be sure to thread the rod end
all the way onto the cylinder rod and then tighten the jam nut to secure the rod end in
place.
11. Use tie wraps (part No. 48RU2313) to secure the one end of the boot to the cylinder
body and the other end to the threaded rod end.
12. Using two nuts (part No. 21AX317), secure the head end of the cylinder to the
mounting bracket, and the rod end of the cylinder to the lower mounting hole in the
clutch release lever.
13. With approximately 3.4″ (86.36 mm) of the rod extended from the cylinder, install the
original clutch dog onto the splines of the clutch release shaft so that the lock bolt is
approximately centered in the slotted hole of the dog. Install the pinch bolt, but do not
tighten at this time.
16

Figure 16 — Install Assist Cylinder Assembly

Key Qty. Part No. Description

1 1 36MX31BM Cylinder, clutch assist
2 1 84AX549 Threaded rod end, male
3 2 21AX317 Lock nut, 7/16-20UNF
4 2 48RU2313 Tie wraps
5 1 8MY428 Boot, cylinder rod
6 1 84AX548 Threaded rod end, female

14. Feed the new clutch cable assembly through the hole in the bulkhead. Use the existing
foam pad, bolts and nuts to secure the cable flange to the bulkhead.

SB313002 — Page 14 of 21
15. Secure the clutch cable clevis to the clutch pedal using the existing clevis pin and
circlip.

When installing the clutch cable, the threaded end of the cable
must not protrude into the clevis at the pedal end of the cable.
DO NOT make any adjustments to the clutch cable in an attempt
to compensate for clutch linkage wear.
17

Figure 17 — Clevis at Pedal End of Clutch Cable

16. Pull the clutch cable return spring back to compress the spring, then slide the cable/
regulator into the slot in the mounting bracket. Release the spring, making sure the
spring seats into the counterbore. Secure the cable flange to the mounting bracket
using two bolts (part No. 77AM16) and two nuts (part No. 154AM5001).
18

Figure 18 — Installing Cable/Regulator Assembly to Mounting Bracket

SB313002 — Page 15 of 21
17. Attach the regulator ball joint to the center mounting hole in the clutch release lever
using a spacer (part No. 35AX634), bolt (part No. 1AX189), flat washer (part No.
37AX68) and nut (part No. 21AX314).
18. Verify that the cylinder rod extends between 3.0″–3.8″ (76.2–96.52 mm) from the
cylinder (measured from the cylinder body to the bottom of the rod end). If not, adjust
clutch cable length by disconnecting the regulator ball joint from the clutch release
lever, loosening the jam nut, then turning the ball joint as required to either lengthen or
shorten the cable. Once the cylinder rod dimension has been properly set, reattach the
regulator ball joint to the clutch release lever.
19

Figure 19 — Adjusting Cylinder Rod Extended Dimension

19. Adjust the clutch dog to obtain 1-1/8″ (28.7 mm) of clutch pedal free play. Clutch pedal
free play must be properly adjusted to obtain the proper 1/8″ (3.3 mm) of clearance
between the clutch release yoke and the release bearing wear pads. Refer to the
“Clutch Pedal Free Play Adjustment” section of this bulletin.
20. Install the 90-degree elbow fitting (part No. 63AX54124) into the port on the air
cylinder.
21. Connect the short air line (part No. 101AX120RF, approximately 8″ [20.32 cm] long)
from the 90-degree elbow fitting in the “AIR OUT” or “R” port in the regulator to the
fitting in the air cylinder. Be sure that the air line is properly looped and there is
sufficient clearance for regulator travel.
20

Figure 20 — Connect Air Line Between Regulator and cylinder

SB313002 — Page 16 of 21
22. Install the elbow fitting (part No. 63AX54124) into the cylinder exhaust port.
23. Cut a length of plastic tubing (part No. 101AX120RF) approximately 62" (1 575 mm)
long, and then connect one end of the tube to the elbow fitting in the assist cylinder
exhaust port.
24. Install the connector fitting (part No. 63AX51438R) into the other end of the plastic
tubing, and then install the bronze filter (part No. 63AX3981).
25. Route the tubing along the clutch cable as shown in the following illustration, and
secure the tubing to the cable with tie wraps (part No. 48RU2313).
21

Figure 21 — Install Remote-Mounted Exhaust Filter

Key Qty. Part No. Description

1 1 63AX3981 Filter, sintered bronze
2 1 63AX51438R Fitting, connector
3 4 48RU2313 Tie wrap
4 1 101AX120RF Tubing (approximately 62" [1 575 mm] long)
5 1 63AX54124 Fitting 90-degree elbow,

26. Cut the air line that runs from the pressure protection valve located at the treadle valve
to the console air manifold.
27. Connect the two ends of the cut air line to the Y-fitting (part No. 63AX3877).

SB313002 — Page 17 of 21
28. Connect a length of air line (part No. 101AX120RF, approximately 38″ [96.52 cm] long)
between the Y-fitting and the “AIR IN” or “P” port in the regulator. Use tie wraps to
secure the line to other air lines as required to prevent rubbing and chafing. Allow
enough slack in the line for proper movement of the line with movement of the
regulator.
22

Figure 22 — Connect Air Line Between Pressure Protection Valve and Regulator
29. Remove the ABC gauge cluster panel from the dashboard to access the clutch switch.
Adjust the clutch switches for proper actuation to compensate for the decrease in
clutch pedal upper travel.
23

Figure 23 — Adjust Clutch Switches

SB313002 — Page 18 of 21
30. Reinstall the ABC gauge cluster panel.
31. Start the engine and allow the air system to build pressure to governor cut-out.
32. Check the clutch release system for proper clutch pedal free play, clutch
disengagement and proper brake squeeze.

Troubleshooting

The following troubleshooting chart summarizes the possible causes and corrective action
for the two most common problems (increased pedal effort and failure of the pedal to fully
return) that may be encountered with the air-operated clutch assist system.

SB313002 — Page 19 of 21
 Symptom Possible Cause Corrective Action
Increased Pedal Effort 1. Damaged or binding clutch 1. Disconnect the clutch cable/
pedal assembly, release lever regulator assembly and the
shaft bearings and/or clevis cylinder from the clutch release
pins. lever, and then check the pedal
assembly, release lever shaft
bearings and the clevis pins for
binding or damage. Replace
components as required
2. Leaking assist cylinder due to 2. With the clutch pedal fully
worn cylinder rod and/or rod depressed, apply a soap and
seal, or internal leakage due to water solution around the
damaged or worn piston seals. cylinder rod seal and around
the sintered bronze filter in the
cylinder exhaust port. There
should be no evidence of
leakage at either location.
Replace the cylinder if leaking
is evident.
3. Air leakage in the clutch 3. Apply a soap and water
release circuit solution to the fittings at the
pressure protection valve,
regulator valve and assist
cylinder inlet port. Replace any
fittings found to be leaking or
defective.
When checking for leakage at
the assist cylinder inlet port,
depress and release the clutch
pedal.
NOTE: Use only OEM fittings
on the air regulator.
4. Binding assist cylinder. 4. Check the assist cylinder for
damage by disconnecting the
cylinder from the release lever
and then moving the rod
through a full stroke. Ensure
that the rod moves freely
through its full length of travel.
Inspect the body of the cylinder
for dents.
Replace the cylinder if any
damage is found, or there are
dents on the body of the
cylinder.
5. Clogged exhaust port filter. 5. Check the sintered bronze filter
located in the assist cylinder
exhaust port. If air does not
pass freely through the filter, it
must be cleaned or replaced.
NOTE: It may be advantageous
to mount the filter in a remote
location to prevent the filter
from clogging with debris. A
length of tubing and suitable
fittings can be used to relocate
the filter in a location such as
inside the frame rail.

SB313002 — Page 20 of 21
 Symptom Possible Cause Corrective Action
Increased Pedal Effort 6. Defective clutch cable/ 6. Check the clutch cable/
(continued) regulator assembly. regulator assembly by
disconnecting the cable from
the clutch pedal and the clutch
release lever, and then
checking the inner cable for
freedom of movement. The
inner cable must move freely
inside the outer cable.
Make sure that the threaded
end of the cable DOES NOT
protrude into the clevis at the
clutch pedal end.
Replace the cable/regulator
assembly if the cable is kinked,
frozen, worn contaminated or
otherwise damaged.
DO NOT lubricate the cable.
7. Low chassis air system 7. Check system pressure at the
pressure. The clutch release regulator supply port. If system
system requires a minimum of pressure at the regulator is
90 psi. below 90 psi, determine the
cause and repair as necessary.
8. Defective regulator. 8. WIth adequate supply pressure
at the regulator, there should
be delivery pressure coming
from the regulator as the clutch
pedal is being pressed. If no
delivery pressure is seen,
replace the cable/regulator
assembly.
Clutch Pedal Does Not Return to 1. Broken return springs. 1. Inspect both the clutch pedal
Fully Released Position return spring and the clutch
cable return spring at the
regulator valve. Replace any
broken springs.
2. Regulator leaking air when 2. Check clutch cable adjustment
clutch is released. and adjust if not within
specifications.
Check for delivery pressure
coming from the regulator with
the clutch pedal released. If
pressure is seen, replace the
clutch cable/regulator
assembly.
3. Same possible causes as listed 3. Check items 1 through 8 above
above for “Increased Pedal and repair, adjust or replace
Effort.” components as required.

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.

SB313002 — Page 21 of 21