CXU, CHU, GU, CXP, CTP SB313005, Air-Operated Clutch ...

1 Service BulletinTrucksMack Trucks, , PA USADateNumberPage1(15)SB313005, Air-Operated Clutch Assist Adjustment and TroubleshootingSB31300501/16/09 CXU, CHU, GU, CXP, CTP(Also applies to mack Trucks Australia, Operation andAdjustment Only, CXX, CLX, CMH, CMM and CSMM odels)(Supersedes SB313005 dated 03/24/08) Air-Operated Clutch Assist Adjustment and TroubleshootingThis service bulletin provides information concerning the Air-Operated Clutch assist system which isstandard equipment on CXU, CHU, GU, CXP and CTP models. Included are exploded views, partnumbers, adjustment procedures and a troubleshooting AND OPERATIONThe air operated Clutch assist system reduces Clutch pedal effort approximately 20%, along with (2 ) less pedal travel. The reduction in Clutch pedal travel results in reduced initial pedal height whichprovides more leg and knee room for the operator.

2 This system increases operator comfort by reducingleg 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 1 Air-Operated Clutch Assist Arrangement01/16/09SB313005 mack Trucks, Bulletin2(15) assembly, Clutch , CXU, CXP, CHU, GU and CTP2648RU2313 Tie wraps3108"101AX120 RFTube, air line 1/4", total length 2 743 mm (108"), mm (38") for supply-to-pressure regulator line, mm (8") for pressure regulator-to-cylinder delivery lineand 1 mm (62") for cylinder exhaust port-to-remote mounted cylinder4125171588 Threaded rod end, male5225090129 Lock nut, 7/16-20 UNF6125097874 Nut, 7/16-20 UNF7263AX54124 Fitting, 90-degree elbow, push-to-connect connector, 1/4" tube, external 1/8" NPTF8121131322 Cylinder, Clutch assist9120956653 Boot, assist cylinder rod10125171587 Threaded rod end, female11135AX634 Spacer1211AX189 Bolt, 5/16-24 UNF-2A x 2-1/2" long13120704998 Flat washer 11/32" ID14120705513 Lock nut, 5/16-24 UNF15225094534 Pan head Torx screw, M6 x x 20 mm long16225161501 Lock nut (with nylon insert), M6 x , flange-head, with patch lock, M12 x x 30 mm longMack Trucks, Bulletin3(15)SB31300501/16/09 Individual components for the Clutch cable assemblies are available separately through the mack PartsSystem.

3 Part numbers are as follows:Effective September 17, 2007, a revised air-assist Clutch cable(part No. 27RC410M) was implemented into production on CXU,CHU and GU models. The revised cable includes a boot on thetransmission end of the cable and an external return spring. Thiscable is a more robust design that is well suited for chassis thatoperate in severe conditions where the possibility of debrisentering the transmission end of the cable exists. If Clutch cablefailure due to dirt intrusion is encountered on a chassismanufactured prior to September 17, 2007, replacement of theexisting cable with the revised cable is recommended. Refer toservice bulletin SB313004 for information concerning the revisedair-assist Clutch 2 Clutch Cable ComponentsCable Assembly Part cable212894-190300239 Regulator312894-195300040 Kit, hardware (includes one threaded rod end, two 90-degree push-to-connect air fittings, one spring and two nuts)4221243492 Fitting5185116896 Rod End01/16/09SB313005 mack Trucks, Bulletin4(15)Air-Assist Clutch System OperationPressure for the Clutch assist is supplied from the pressure protection valve located on the treadle the Clutch pedal is pushed in to disengage the Clutch , movement of the Clutch cable opens thepressure regulator to allow air flow to the rod end of the cylinder.

4 The amount of force placed on theclutch cable determines how much pressure is delivered by the regulator. As pressure enters thecylinder, the cylinder rod retracts and pulls the Clutch release lever. The action of the assist cylinderpulling the release lever reduces the amount of pedal effort required to disengage the 3 Air-Operated Clutch Assist Air Flow Diagram (Disengaging Clutch ) mack Trucks, Bulletin5(15)SB31300501/16/09 When the Clutch pedal is released to engage the Clutch , the pressure regulator closes and shuts off theflow of air to the cylinder. The return spring (integral with the Clutch cable assembly) returns the releaselever to its home position, and the returning release lever pulls the rod from the cylinder. As the rodextends, pressure inside the cylinder exhausts through an exhaust port in the regulator 4 Air-Operated Clutch Assist Air Flow Diagram (Engaging Clutch ) Clutch Release Cylinder ExhaustAs the Clutch pedal is pushed in to disengage the Clutch , the assist cylinder rod retracts into the trapped in the head-end of the cylinder exhausts through the exhaust port at the rear of the the Clutch pedal is released to engage the Clutch , the cylinder rod extends.

5 As the rod extends, airis drawn back into the cylinder through the exhaust prevent debris from entering the cylinder, a sintered bronzefilter is incorporated into the exhaust port. The filter is securedapproximately mid-way up the Clutch cable, and is connected tothe cylinder exhaust port with a 1/4" plastic tube. With thisarrangement, however, the possibility exists for moisture to bedrawn into the cylinder, which can cause corrosion inside thecylinder and result in sticking or binding Clutch operation. Toprevent this from occurring, the vent line can be relocated to theclutch cable mounting tube located on the cab bulkhead. Referto service bulletin SB313003 for information on relocating thecylinder Trucks, Bulletin6(15) Clutch ADJUSTMENT PROCEDURESV erify Release Bearing TravelIn order for the Clutch to release properly, the Clutch release bearing must travel between mm(1/2" 9/16"), and there must be mm (1/8 ) of clearance between the Clutch release yoke and therelease bearing wear pads.

6 The specified clearance between the Clutch release yoke and the releasebearing wear pads equates to mm (1-1/8") of Clutch pedal free travel in the the Clutch properly adjusted, Clutch brake squeeze should occur within the last mm(1/4" 3/8") of pedal travel or gap between the release bearing and Clutch brake are adjusted by the internal clutchring. Clutch brake/ Clutch pedal free travel is adjusted by varying the length of the external adjustment procedures are as follows:Before working on the vehicle, apply the parking brakes,place the transmission in neutral and block the to do so can result in unexpected vehicle movementand can cause serious personal injury or will need an assistant to hold the Clutch pedal down (clutchreleased) to adjust release bearing free travel in all but theSachs Twin Extend wear appropriate eye protection to prevent the riskof eye injury.

7 Keep your hand/fingers away from Trucks, Bulletin7(15)SB31300501/16/09 Verify and Adjust Clutch Brake SqueezeVerify that Clutch brake squeeze occurs within the last mm (1/4" 3/8") of Clutch pedal brake squeeze is verified as follows:5 Figure 5 Verify Clutch Brake SqueezeUse a gauge long enough to keep hands away from Remove the inspection cover from the transmission bell Insert a mm ( ") thickness gauge between the rear face of the Clutch release bearing andthe Clutch Have an assistant fully depress the Clutch pedal and then slowly release the pedal. Tell the assistantto stop releasing the pedal as soon as the thickness gauge can be pulled from between the releasebearing and the Clutch Measure the gap between the pedal and the pedal stop. If Clutch brake squeeze does not occurwithin the last mm (1/4" 3/8") of pedal travel, adjust as follows:6 Figure 6 Clutch Brake Squeeze Adjustment1.

8 Adjusting Bolt2. Jam Nut3. Clutch Dog4. Clutch Dog Lock Bolt01/16/09SB313005 mack Trucks, Bulletin8(15) the Clutch dog lock the adjusting bolt jam the adjusting bolt to properly set Clutch brake squeeze. Turning the adjusting bolt clockwise results in Clutch brake squeeze occurring furtherfrom the end of pedal travel (increases dimension). Turning the adjusting bolt counterclockwise results in Clutch brake squeeze occurringcloser to the end of pedal travel (decreases dimension).5. When Clutch brake squeeze has been properly set, tighten the Clutch dog bolt and the adjusting boltjam Clutch Pedal Free PlayAfter establishing the correct Clutch brake squeeze, verify Clutch pedal free play. Check for mm (1/8")of clearance between the Clutch release yoke and the release bearing wear pads. Pedal free travel forthe cable-operated air-assist Clutch release system should be mm (1-1/8" 1/4").

9 Thereshould be approximately mm (3" ") of cylinder rod visible when measured from thecylinder body to the bottom of the cylinder rod end. This dimension ensures that the cylinder will notbottom when the Clutch pedal is pushed in ( Clutch disengaged). If the free play is inadequate investigateif the Clutch cable, assist cylinder or mounting brackets are secured 7 Clutch Pedal Free PlayAdjustments for the different model clutches are as follows:Eaton Easy-Pedal :1. Using the appropriate engine turning tool, rotate the engine in the direction of normal rotation untilthe Kwik-Adjust component is visible through the bell housing inspection Have an assistant fully depress the Clutch pedal ( Clutch released).3. Insert a 5/8" socket or box wrench through the inspection hole and over the hex-head bolt on theKwik-Adjust While pedal is held down, push adjusting nut and measurement was more that mm ( ") turn adjusting nut measurement was less that mm ( ") turn adjusting nut ValueClutch :1.

10 Using the appropriate engine turning tool, rotate the engine in the direction of normal rotation untilthe Lockstrap is visible through the bell housing inspection Trucks, Bulletin9(15)SB31300501/16/092. Have an assistant fully depress the Clutch pedal ( Clutch released).3. While pedal is held down, remove the lockstrap and move the adjusting measurement was more that mm ( ") move the adjusting lug to the measurement was less that mm ( ") move the adjusting lug to the Solo Clutch :1. Initially adjust the linkage until the yoke fingers contact the release bearing (zero pedal free play).2. Press the pedal to the floor up to 5 times, this: Moves the release bearing closer to the transmission. Gains free play in the With the pedal up, measure the distance between the release bearing and the Clutch the distance is more that mm ( ") return to step 1 and readjust the Clutch linkage.