Chapter 14

1. Chapter 14 Clutches

2. Objectives (1 of 2) • Outline the operating principles of a clutch. • Identify the components of a clutch assembly. • Explain the differences between pull-type and push-type clutches. • Describe the procedure for adjusting manual and self-adjusting clutches. • Explain how to adjust the external clutch linkage.

3. Objectives (2 of 2) • Describe the function of a clutch brake. • Troubleshoot a clutch for wear and damage. • Outline typical clutch defects and explain how to repair them. • Outline the procedure for removing and replacing a clutch.

4. Clutches with Coil Springs • In some clutches, coil springs are positioned perpendicular to the pressure plate. • Other clutches use fewer coil springs and angle them between the cover and a retainer. • Angle-spring designs require 50 percent less clutch pedal effort. • They also provide a constant plate load regardless of the thickness or wear on the friction facings of the driven discs. • When the clutch is adjusted, the pressure plate position does not move; rotating the adjusting ring moves the levers toward the transmission.

5. Diaphragm Springs • Diaphragm or Belleville spring clutches provide for less pedal effort. • They use either a single disc or multiple discs. • They can also be either a push-type or pull-type clutch. • A diaphragm clutch using Belleville spring maintains the same amount of pressure at the new and fully worn positions.

6. Intermediate Plate (1 of 2) • A clutch with two friction discs uses an intermediate plate to separate the discs. • It increases the torque capacity of the clutch by increasing the contact friction area. • Some intermediate plates have drive slots machined in their outer edge. These slots fit over and are driven by hardened steel drive pins press-fit into holes in the flywheel rim.

7. Intermediate Plate (2 of 2) • Other intermediate plates have four or more drive lugs that fit to, and are driven by, slots in the clutch cover. • Some clutches with heavy-duty intermediate plates require anti-rattle springs to reduce wear and improve clutch release. • Adapter ring • Some two-plate clutches use an adapter ring when the clutch is installed on a flat flywheel.

8. Clutch Adjustment Mechanisms • Manually adjusted clutches • A manual adjusting ring permits the clutch to be adjusted to compensate for friction facing wear. • Self-adjusting clutches • The adjusting ring has teeth that mesh with a worm gear in a wear compensator. • As the retainer moves forward each time the clutch is engaged, an actuator arm rotates the worm gear in the wear compensator. • Rotation of the worm gear is transferred to the adjusting ring, removing slack between the pressure plate and the driven discs.

9. Disc Design • Rigid discs are steel plates to which friction linings, or facings, are bonded or riveted. • A rigid disc cannot absorb torsional shock loads and its misapplication can damage the transmission and input shaft. • Torsional vibration can also cause a rigid disc to crack. • Dampened discs have coaxial dampening springs incorporated into the disc hub. • When engine or driveline torque is first transmitted to the disc, the plate rotates on the hub, compressing the springs. This action absorbs the shock and torsional vibration caused by low rpm, high-torque engines. • The cushioning effect extends clutch life and protects other driveline components from torsional overloads.

10. Friction Facings • Organic friction facings are made from non-asbestos materials such as glass, mineral wool, and carbon. • Grooves in the facing allow worn particles to be thrown off rather than accumulating on the face of the disc. • Ceramic friction facings are made from a mixture of ceramics and copper or iron. • They have a higher coefficient of friction, heat tolerance, and torque capacity than organic friction facings. • Ceramic friction facings grab quicker with less slip. • They also offer a longer service life. • Ceramic friction facings consist of small pads or buttons riveted to a disc or isolator. • Kevlar friction facings are used in some after-market applications. These are said to be able to sustain greater abuse.

11. Push-type Clutches • The release bearing is pushed toward the engine. • When the pedal of a push-type clutch is initially depressed, there is some free pedal movement between the fork and the release bearing (normally about 1/8 inch). • As the release bearing moves toward the engine, it acts on release levers bolted to the clutch cover assembly, forcing the pressure plate to move away from the clutch discs. • This compresses the springs and disengages the discs. • This type of clutch has no provisions for internal adjustment. All adjustments normally are made externally via the linkage system.

12. Pull-type Clutches • A pull-type clutch pulls the release bearing (which is attached to the clutch cover by a sleeve and retainer assembly) toward the transmission. • This compresses the springs and moves the pressure plate, relieving pressure acting on the friction discs. • This action allows the driven disc or discs to float freely between the plate(s) and the flywheel. • Pull type clutches are used in both medium- and heavy-duty applications and are adjusted internally.

13. Clutch Brakes • Its purpose is to slow or stop the transmission input shaft from rotating to allow gears to be engaged without clashing (grinding). • Only 70 to 80 percent of clutch pedal travel is needed to fully disengage the clutch. The last 1/2 to 1 inch of pedal travel is used to engage the clutch brake. • When the pedal is fully depressed, the release bearing presses against the clutch brake which acts to stop the transmission input shaft. • Conventional clutch brake • Limited torque clutch brake • Torque-limiting clutch brakes • Two-piece clutch brakes

14. Conventional Clutch Brake • A conventional clutch brake consists of a steel washer faced on both sides with friction material, or discs. • The steel washer has two tangs that engage machined slots in the transmission input shaft. • This mounting arrangement allows the brake to slide back and forth on the input shaft, while turning with the shaft. • Conventional clutch brakes are designed to be used when shifting from neutral to first or reverse. • Unlike some clutch brakes, a conventional clutch brake is not used to aid upshifting.

15. Limited Torque Clutch Brake • A limited torque clutch brake enables faster upshifts in addition to shifting into first and reverse. • When the truck is moving and the clutch brake is engaged, it slows the transmission input shaft, allowing the speed of the transmission input shaft to synchronize quickly with the transmission countershafts.

16. Torque-limiting Clutch Brakes • They are designed to slip when torque loads of 20 to 25 pound-feet are reached. • This protects the brake from overloading and heat damage. • This type of clutch brake is used only when shifting into first or reverse while the vehicle is stationary.

17. Two-piece Clutch Brakes • Sold by aftermarket suppliers • Can be quickly installed without removing the transmission • Do not damage the transmission input shaft when cutting out the defective clutch brake with an oxyacetylene torch.

18. Mechanical Clutch Linkage • Mechanical linkages used in heavy-duty trucks • The first uses levers to multiply pedal pressure applied by the driver. • The second type links the clutch pedal and release fork by means of clutch control cable.

19. Hydraulic Clutch Linkage • The clutch is disengaged by hydraulic fluid pressure sometimes assisted by an air servo cylinder. • A typical system: • Master cylinder • Hydraulic fluid reservoir • Air-assisted servo cylinder • Rigid and flexible hydraulic lines

20. Solo Clutches • Adjustment-free clutches such as the Eaton Fuller Solo medium- and heavy-duty clutch family claims zero maintenance during the life of the clutch. • A wear indicator is used to: • Monitor remaining clutch life and provide an alert when replacement is required • Once the clutch pack assembly has been correctly set up, the release bearing position is maintained as the clutch wears, and free travel is maintained. • The release bearing requires grease on a PM schedule. • Adjustment is verified only during an inspection.

21. Clutch Adjustments • Too much free pedal prevents complete disengagement of the clutch. • Too little free pedal causes clutch slippage, heat damage, and shortened clutch life. • As the friction disc facings wear through normal operation, free pedal will gradually decrease. • If inspection indicates clutch free pedal travel is less than 1/2 inch, adjustment of the clutch is required. • Do not wait until no free pedal exists before making this adjustment.

22. Pull-type Clutch Adjustment • Pull-type clutches may require a two-step adjustment to obtain the specified free travel and free pedal specifications. • The first step is a release bearing free travel adjustment that may not be required. • The second step is a pedal or linkage adjustment. • The free travel adjustment should be performed first. Free travel adjustment is usually an internal adjustment; however, some clutch models are equipped with an external quick-adjust mechanism.

23. Internal Adjustment Mechanisms Angle Spring Clutch • There are three basic types of adjustment mechanisms currently in use on angle coil spring clutches used in heavy-duty truck applications. • Two are manual-adjusting mechanisms and the third category includes several types of self-adjusting mechanisms. • Lock-strap mechanism • Kwik-adjust mechanism • Wear compensator

24. Kwik-adjust Mechanism • The adjustment is made using a socket wrench to turn the adjusting bolt. • Using a 3/4-inch socket (12 point) or box-end wrench, depress the adjusting nut and rotate to make the adjustment. The Kwik-adjust will reengage at each quarter turn. • Ensure that the adjusting nut is locked in position with the flats aligned to the bracket.

25. Clutch Brake Setting • Insert a 0.010-inch thickness gauge between the release bearing and the clutch brake. • Depress the clutch pedal until the thickness gauge is squeezed firmly. • Let the pedal up slowly until the gauge can be pulled out and note the position of the pedal in the cab. It should be 1/2 to 1 inch from the end of the pedal stroke. • To adjust the clutch brake setting, shorten or lengthen the external linkage according to service literature procedure. If the specified adjustment cannot be obtained, check the linkage for excessive wear and pedal height. • Reinstall the inspection cover.

26. Clutch Servicing • When it is determined that the clutch is not operating properly and is in need of servicing, the transmission and clutch cover assembly must be removed to access the clutch pack assembly. • Parts that are worn or damaged must be replaced. • If the pressure plate, springs, release levers, etc., are damaged, the complete clutch assembly should be replaced. • Clutch rebuilding is usually performed only by clutch specialty rebuilding shops.

27. Pilot Bearing Replacement • Whenever the clutch is serviced or the engine is removed, the pilot bearing in the flywheel should be removed and replaced. • Use an internal puller or a slide hammer to remove the pilot bearing. • Discard the used pilot bearing.

28. Clutch Inspection • Check the following surfaces: • Flywheel housing • Transmission clutch housing • Flywheel • Measure the run-out of: • Flywheel outer surface • Flywheel housing pilot • Flywheel housing face • Pilot bearing bore • Check the crankshaft endplay.

29. Intermediate Plate • Drive slots and tabs • On 14-inch clutches, inspect the slots for the drive pins. • On 15-½-inch clutches, inspect the tabs on the outer edge. • Cracks • Make sure the plate is not cracked. • Heat damage • Heat discoloration is a normal condition. • Heat discoloration can be removed with an emery cloth. • If heat discoloration cannot be removed, replace the center plate. • Thickness • Use a micrometer or caliper to measure the thickness. • Warpage • Make sure the center plate is flat and not warped by measuring runout.

30. Pilot Bearing • Although the pilot bearings should be replaced whenever the clutch is removed, inspect the used pilot bearing for wear and damage. • Determine and correct the cause of the wear and damage.

31. Caution • Tap on the outer race of the pilot bearing only. • Make sure it is seated properly in the bearing bore. • This bearing must have a press fit within the pilot bearing bore. Never stake a loose pilot bearing, because it will eventually spin in the bore.

32. Caution • Some heavy-duty clutches have thicker intermediate plates and thinner super buttons than standard clutches. • Do not intermix these components.

33. Solo Clutch Problems • Use Eaton/Dana service literature to troubleshoot Solo clutches. • The Solo Heavy Duty Troubleshooting guide (CLTS-1295) is a free download from www.roadranger. com.

34. Summary (1 of 6) • The components of a clutch assembly can be grouped into two basic categories: driving members and driven members. • Driving members include the flywheel, clutch cover, pressure plate, pressure springs and levers, intermediate plate, adapter ring, and adjustment mechanisms. • Driven members include friction discs and the transmission input shaft. • A clutch can be released or disengaged by one of two methods: push-type clutch or pull-type clutch.

35. Summary (2 of 6) • Clutch brakes are found in some pull type clutches and can be grouped into four types: conventional, limited torque, torque-limiting, and two-piece clutch brakes. • The clutch linkage, which connects the clutch pedal to the release fork or yoke, can be one of three types: mechanical, hydraulic, and air control.

36. Summary (3 of 6) • Clutches should be checked periodically for proper adjustment and lubrication. • The major cause of clutch failure is excess heat. • Most heat-related damage is related to driver abuse. • Heat damage results from starting in the incorrect gear, shifting or skip-shifting, riding the clutch pedal, and improper coasting.

37. Summary (4 of 6) • Free pedal, or pedal lash, is the amount of free play in the clutch pedal in the cab. • This measurement is directly related to free travel, which is the clearance distance between the release yoke fingers and the clutch release. • There are two basic manual adjustment methods used on angle coil spring clutches: (lockstrap and Kwik-Adjust).

38. Summary (5 of 6) • Adjustment-free clutches such as the Solo clutch should automatically adjust for the life of the clutch pack. • The only maintenance required is periodic lubrication of the release bearing mechanism. • Pull-type clutches with perpendicular springs use a threaded sleeve and retainer assembly that can be adjusted to compensate for disc lining wear.

39. Summary (6 of 6) • Asbestos and non-asbestos fibers could pose a health risk. Technicians should take the appropriate safety precautions when servicing clutches. • The following should be checked in a clutch inspection. • Transmission bell housing, flywheel housing, flywheel drive pin, release fork and shaft, input shaft, pressure plate and cover assembly, clutch discs, friction facings, center plate, and pilot bearing.