Chapter 14 Clutches

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.

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.

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. Most clutch designs use multiple coil springs to force the plate against the driven discs. In some clutches, coil springs are positioned perpendicular to the pressure plate and are equally spaced around the perimeter of the cover (Figure 14–5). Other clutches use fewer coil springs and angle them between the cover and a retainer (Figure 14–6). 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. The angle- spring clutch illustrated in Figure 14–6 operates under indirect pressure. Three pairs of coil springs are located away from the pressure plate rather than directly on it. Spring load is applied through a series of six levers. In this clutch design, the plate load and release bearing load are not directly proportional to the spring load. The engaged position of a new angle spring clutch is shown in Figure 14–7A. Pressure plate load is the result of the axial load of the springs multiplied by the lever ratio. The pressure springs are positioned at an angle to the center line of the clutch with each end attached to the flywheel ring (cover) and the release sleeve retainer. As the release sleeve retainer—including the release sleeve and release bearing—is moved toward the flywheel, the springs pivot freely without bending or buckling. Connected to the retainer are levers that, when forced forward by the retainer, multiply the force of the springs. Pivot points on the levers press the pressure plate against the driven discs. When the clutch pedal is released (Figure 14–7B), spring load increases but axial load decreases, resulting in reduced pedal effort. The plate load is defined by the axial spring force multiplied by the lever ratio. Axial spring force changes with release bearing movement, but not in direct proportion to the spring load. When friction facings wear (Figure 14–7C), spring load reduces but axial load remains constant. As the clutch wears, the release sleeve assembly moves toward the flywheel, and the pressure springs elongate, reducing their tension. The axial spring force, however, remains essentially constant. This means that pressure plate force remains constant throughout the life of the clutch. When the clutch is adjusted to compensate for friction facing wear, the pressure plate position does not move, but the rotating adjusting ring moves the levers toward the transmission, pushing the release sleeve and bearing assembly in that direction also. This re-establishes the internal spring position to the original setting for continued clutch use.

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. Clutches equipped with a diaphragm or Belleville spring assemblies are often used in medium-duty trucks. Like coil spring-equipped clutches, diaphragm and Belleville spring clutches operate under indirect pressure using a retainer and lever arrangement to exert pressure on the pressure plate. The levers may also be referred to as fingers or tapered fingers. As with angle-spring clutches, the result is low release bearing load and constant pressure plate load. Pressure plate load on the friction material surface varies by the thickness of the diaphragm spring. This type of clutch uses either a single disc or multiple discs with the addition of an intermediate plate. It can also be designed either as a push-type or pull- type clutch. The actual design used is determined by the clutch linkage/vehicle design, space requirements inside the vehicle, and the torque load required from the clutch assembly. In the diaphragm clutch assembly shown in Figure 14–8, the clutch cover assembly is bolted directly to the engine flywheel. The clutch cover assembly drives the pressure plate by means of drive straps. In a push-type clutch, pressing the clutch pedal moves the release bearing towards the engine flywheel. As the clutch’s diaphragm spring fingers are depressed, the pressure plate retracts from contact with the driven disc(s) and the clutch is disengaged. When the clutch pedal is released, the release bearing and clutch diaphragm spring fingers move away from the engine flywheel. The diaphragm Belleville spring exerts pressure through its levers to the pressure plate. This results in the driven disc(s) being locked up between the friction surfaces of the pressure plate and the engine flywheel in the single disc type. Torque flow through a multiple disc assembly is the same as with a coil spring or angle spring type. The pressure plate diaphragm Belleville spring exerts pressure through the rear disc to the intermediate plate and to the forward disc onto the flywheel friction face. This locks the clutch assembly together. On a conventional direct pressure clutch, as the friction facings wear, pressure plate load loss occurs as a result of spring elongation. A diaphragm clutch that uses a Belleville spring design maintains the same plate load at the new and fully worn positions (Figure 14–8A & C).

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. Intermediate Plate In a clutch with two friction discs, an intermediate, or center, plate separates the discs. The plate is machined smooth on both sides because it is clamped between two friction surfaces. An intermediate plate 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. (See Figure 14–2) 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 antirattle springs (Figure 14–9). These reduce wear between the intermediate plate and the drive pins, and improve clutch release. Without the springs, the drive slots in the plate would wear excessively, resulting in poor clutch release. Three or four antirattle springs are positioned between the edge of the plate and the inside wall of a pot type flywheel. These are spaced equal distances apart (three springs—120 degrees apart; four springs—90 degrees apart) Some two-plate clutches use an adapter ring when the clutch is installed on a flat flywheel. The adapter ring is bolted between the clutch cover and the flywheel. It is sized to provide the needed depth to accommodate the second clutch disc and the intermediate plate.

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.

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. Manually Adjusted Clutches These clutches have a manual adjusting ring that permits the clutch to be adjusted to compensate for friction facing wear. The ring is positioned behind the pressure plate and is threaded into the clutch cover. A lock strap or lock plate secures the ring so that it cannot turn during normal operation. When the lock strap is removed, the adjusting ring can be rotated in the cover to adjust for wear. This forces the pivot points of the levers to advance, pushing the pressure plate forward and compensating for wear. A manual adjusting ring is shown in Figure 14–4. Self-Adjusting Clutches. Self-adjusting clutches automatically take up the slack between the pressure plate and clutch disc as wear occurs. The adjusting ring has teeth that mesh with a worm gear in a wear compensator (Figure 14–10). The wear compensator is mounted in the clutch cover and has an actuator arm that fits into a hole in the release sleeve retainer (Figure 14–11). As the retainer moves forward each time the clutch is engaged, the actuator arm rotates the worm gear in the wear compensator. Rotation of the worm gear is transferred to the adjusting ring in the clutch cover, removing slack between the pressure plate and the driven discs.

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. Disc Design There are two basic disc designs: rigid dampened (Figure 14–12). Rigid discs are steel plates to which friction linings, or facings, are bonded or riveted. Rigid discs are most often used in two-plate clutches where the torque loads can be distributed over a greater surface area. 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. Most manufacturers specify the use of dampened discs in trucks equipped with high-torque-rise engines. 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.

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. Friction Facings Friction facings are critical to clutch life and performance because they directly receive the torque of the engine any time the clutch is engaged. There are two types of friction facings: organic and ceramic (Figure 14–12). Most organic friction facings are made from non-asbestos materials such as glass, mineral wool, and carbon. Organic friction facings are usually molded to the full surface of the disc and are called “full faced.” Grooves in the facing allow worn particles to be thrown off rather than accumulating on the face of the disc. Today, organic friction facings are usually specified on light-duty trucks. 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, making them popular on pick-up and delivery (P&D) vehicles, vocational trucks, and line-haul applications. Ceramic friction facings consist of small pads or buttons riveted to a disc or isolator. The disc can be round with slots machined in it between each button or it might be a scalloped, paddle wheel configuration. Three, four, or more buttons can be installed on each face of the disc. Kevlar friction facings are used in some after-market applications: These are said to be able to sustain greater abuse.

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. Push-type Clutches In a push-type clutch (Figures 14–13 and 14–14), the release bearing is not attached to the clutch cover. To disengage the clutch, 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). After the initial movement, the clutch release fork contacts the bearing and forces it toward the engine. As the release bearing moves toward the engine, it acts on release levers bolted to the clutch cover assembly. As the release levers pivot on a pivot point, they force the pressure plate (to which the opposite ends of the levers are attached) to move away from the clutch discs. This compresses the springs and disengages the discs from the flywheel, allowing the disc (or discs) to float freely between the pressure plate and flywheel, breaking the torque between the engine and transmission. When the clutch pedal is released, spring pressure acting on the pressure plate forces the plate forward once again, clamping the plate, disc, and flywheel together and allowing the release bearing to return to its original position. Push-type clutches are used predominantly in light- and medium-duty truck applications in which a clutch brake is not required. This type of clutch has no provisions for internal adjustment. All adjustments normally are made externally via the linkage system.

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. Pull-type Clutches As the name implies, a pull-type clutch does not push the release bearing toward the engine; instead, it pulls the release bearing toward the transmission. In clutches with angled coil springs or a diaphragm spring, the release bearing is attached to the clutch cover by a sleeve and retainer assembly (Figure 14–15 and Figure 14–16). When the clutch pedal is depressed, the bearing, sleeve, and retainer are pulled away from the flywheel. This compresses the springs and causes the pivot points on the levers to move away from the pressure plate, relieving pressure acting on the pressure plate. This action allows the driven disc or discs to float freely between the plate(s) and the flywheel. On pull-type clutches with coil springs positioned perpendicular to the pressure plate (Figure 14–17), the release levers are connected on one end to the sleeve and retainer; on the other end they are connected to pivot points (Figure 14–18). The pressure plate is connected to the levers near the pivot points. So, when the levers are pulled away from the flywheel, the pressure plate is also pulled away from the clutch discs, disengaging the clutch. When the clutch pedal is released, spring pressure forces the pressure plate forward against the clutch disc and the release bearing, sleeve, and retainer return to their original position. Pull type clutches are used in both medium- and heavy-duty applications and are adjusted internally.

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 CLUTCH BRAKES Most pull-type clutches have a component not found on push-type clutches: a clutch brake. The clutch brake is a disc with friction surfaces on either side; it is mounted on the transmission input shaft splines between the release bearing and the transmission (Figure 14–19A). Its purpose is to slow or stop the transmission input shaft from rotating to allow gears to be engaged without clashing (grinding). Clutch brakes are used only on vehicles with nonsynchronized transmissions. Only 70 to 80 percent of clutch pedal travel is needed to fully disengage the clutch. The last ½ to 1 inch of pedal travel is used to engage the clutch brake. When the pedal is fully depressed, the fork squeezes the release bearing against the clutch brake, which forces the brake disc against the transmission input shaft bearing retainer (Figure 14–19B). The friction created by the clutch brake facing stops the rotation of the input shaft and countershaft. This allows the transmission gears to mesh without clashing.

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. Conventional Clutch Brake 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. 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.

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. Limited Torque Clutch Brake A limited torque clutch brake (Figure 14–20) 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. Quicker engagement results in faster shifts.

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. Torque-limiting Clutch Brakes A torque-limiting clutch brake (Figure 14–21) is designed to slip when torque loads of 20 to 25 pound-feet are reached. This protects the brake from overloading and the resulting heat damage. As shown in Figure 14–22, a torque-limiting clutch brake has a hub and Belleville washers inside a cover. The hub and washers are designed to slip when a specified torque is exceeded. This type of clutch brake is used only when shifting into first or reverse while the vehicle is stationary.

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. Two-Piece Clutch Brakes The two-piece clutch brake design is sold by aftermarket suppliers (Figure 14–23). It can be quickly installed without removing the transmission. Great care should be taken not to damage the transmission input shaft when cutting out the defective clutch brake with an oxyacetylene torch.

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. Mechanical Clutch Linkage Two types of mechanical linkages are used in heavy duty trucks: The first uses levers to multiply pedal pressure applied by the driver, and the second type links the clutch pedal and release fork by means of clutch control cable. Examples of both types are shown in Figure 14–25 and Figure 14–26. Components in each type vary, depending on the truck chassis manufacturer.

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 Hydraulic Clutch Linkage Figure 14–27 shows the components of a typical hydraulic clutch control system. The clutch is disengaged by hydraulic fluid pressure sometimes assisted by an air servo cylinder. The clutch in Figure 14–27 consists of a master cylinder, hydraulic fluid reservoir, and an air-assisted servo cylinder. The components are all connected by rigid and flexible hydraulic lines. When a truck driver depresses the clutch pedal, an actuating plunger forces the piston in the master cylinder to move forward. This movement closes off the reservoir and forces hydraulic fluid through the circuit to a reaction plunger and pilot valve in the servo cylinder. Hydraulic pressure forces the reaction plunger to move forward to close off an exhaust port and to seat the pilot valve. When the plunger is moved farther, it unseats the pilot valve, which allows air to enter the servo cylinder, exerting pressure onto the rear side of the air piston. The movement of the air piston assists in clutch pedal application. As clutch pedal pressure increases, the air piston is moved farther forward and air pressure overcomes the hydraulic pressure in the reaction plunger. This causes the pilot valve to reseat, preventing any more air from reaching the air piston. The pilot valve and reaction plunger remain in this position until there is a change in the pressure. When the hydraulic pressure decreases, the return spring returns the reaction plunger and the pilot valve seats itself, which in turn uncovers the exhaust port and allows the air to exhaust from the servo cylinder.

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. Solo Clutches Adjustment-free clutches such as the Eaton Fuller Solo medium- and heavy-duty clutch family have become popular recently due to claims of 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. You should know how to verify the adjustment of a Solo clutch and this procedure is covered at the end of this chapter; adjustment is verified only at inspection.

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. As mentioned earlier, clutch free pedal, or the initial free travel of the clutch pedal, should be 11/2 to 2 inches for both push-type and pull-type clutches. Free pedal is determined by placing your hand or foot on the clutch pedal and gently pushing it down until an increase in push effort is felt. Movement after this point will cause the release bearing to begin disengaging the clutch. In a push-type clutch, free pedal is set to 11/2 to 2 inches to obtain the desired 1/8-inch free travel clearance between the clutch release bearing and clutch release levers (Figure 14–31), or diaphragm spring,whichever is used. Some transmission housings have grease fittings where the clutch release cross shaft passes through the housing bosses. In a push-type clutch, the desired free travel clearance is 1/8 inch. Total release bearing travel in a push-type clutch must be approximately 5/8 inch. In a pull-type clutch, the 1/8-inch free travel clearance occurs between the release yoke fingers and the clutch release bearing pads This = 1/8” free travel at the release bearing should produce 11/2” of free pedal. Free pedal dimensions are greater than free travel at the release bearing specifications because as movement transfers through the linkage, it is amplified. 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. Remember that the method of setting free pedal and free travel is different between push-type clutches and pull-type clutches. Use the correct method for adjusting each type of clutch and refer to the service manual for specifications and setting procedures.

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. 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.

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 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. Lockstrap Mechanism. The lockstrap mechanically locks the clutch adjusting ring and, when removed, permits adjustment of free travel. To adjust a clutch:

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. Kwik-Adjust Mechanism. This manual adjust mechanism (Figure 14–37) permits free travel adjustment without the use of special tools or removing bolts. 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 (Figure 14–38). 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.

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. Clutch Brake Setting To check the clutch brake setting, depress the clutch pedal in the cab and note the point at which the clutch brake engages by observation through the inspection cover. With the release travel and free travel settings, clutch brake squeeze should occur approximately 1 inch from the end of the pedal stroke (Figure 14–34). To check this: Insert a 0.010-inch thickness gauge between the release bearing and the clutch brake. Depress the clutch pedal to squeeze the thickness gauge. 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.

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. 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. Generally, components of the clutch pack assembly are not serviceable separately. As a rule, if the pressure plate, springs, release levers, etc., are damaged, the complete clutch assembly should be replaced. Today, clutch rebuilding is usually performed only by clutch specialty rebuilding shops. The following sections explain how to remove a clutch, inspect clutch components for damage, and install a clutch.

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.

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. CLUTCH INSPECTION After removing the clutch from the flywheel, inspect the clutch components for damage or signs of wear. It is important that the cause of wear be determined and the problem corrected. Transmission Clutch Housing and Flywheel Surfaces The engine and transmission must be in alignment. To check this, perform the following inspection procedure. Surfaces being indicated must be clean for accurate measurements. Inspect the surface face of the flywheel for wear or damage. Make sure that the flywheel is not cracked. Minor heat discoloration is a normal wear condition that can be removed with an emery cloth. Some wear or damage can be removed by machine grinding the flywheel face. If wear or damage on the flywheel cannot be removed, it must be replaced. Inspect the teeth of the ring gear on the outer surface of the flywheel. If the teeth are worn or damaged, replace the ring gear or the flywheel and inspect the starter drive teeth. Inspect the mating surfaces of the transmission bell housing and the engine flywheel housing (Figure 14–55). Wear on either housing flange will result in misalignment. Wear will usually occur on the lower half of these surfaces, with the most wear occurring between 3 o’clock and 8 o’clock positions Flywheel Outer Surface Runout. To make this check: Secure a dial indicator to the flywheel housing with the gauge finger on the flywheel near the outer edge (Figure 14–56). Zero the dial indicator. Manually rotate the flywheel one revolution in the direction of engine rotation. On some engines the crankshaft can be rotated by putting a socket on the nut that holds the pulley on the front of the crankshaft or by a toothed ratchet that engages to the ring gear teeth. If access to the front of the crankshaft is difficult, use a spanner wrench on the teeth of the flywheel to rotate the crankshaft. Record the reading on the dial indicator, marking the high and low points. The acceptable runout on the outer surface of the flywheel is a specified amount multiplied by the diameter of the flywheel in inches. For a 14-inch clutch, and 0.008 inch or less; for a 151/2-inch clutch. Check service manual specifications for exact tolerances. Checking Flywheel Housing Pilot Runout. Secure the dial indicator to the crankshaft. With the dial gauge plunger against the housing pilot, rotate the crankshaft one revolution in the direction of engine rotation (Figure 14–57). Use a marker or soapstone to mark the high and low points and record dial indicator readings. Total difference between high and low points should not exceed manufacturer’s specifications, which normally range between 0.006 and 0.015 inch. If runout exceeds specifications, service the flywheel as required. Checking Flywheel Housing Face Runout. Proceed as follows: 1. Position the dial gauge plunger to contact the face of the engine flywheel housing (Figure 14–58). As described above, rotate the crankshaft through one revolution marking high and low points. Typically, the total difference between the high and low points should not exceed 0.008 inch. Checking Runout on the Pilot Bearing Bore. Install a dial indicator so that the base of the indicator is on the mounting surface of the flywheel housing. Ride the plunger of the dial indicator against the pilot bearing bore (Figure 14–59). Manually turn the crankshaft one revolution in the direction of the engine rotation. Record the reading on the dial indicator. Maximum runout for the surface of the bore of the pilot bearing is typically 0.005 inch. If runout exceeds specifications, service the crankshaft as required. If these limits are exceeded, the problem must be corrected or misalignment will cause premature wear to the drivetrain components. Check Crankshaft Endplay. Install a dial indicator so that the base of the indicator is on the flywheel housing. Set the plunger of the dial indicator against the hub of the flywheel (Figure 14–60). Force the flywheel fore and aft and record the indicated reading. Check the indicated reading against the specification of the engine manufacturer.

Intermediate Plate Drive slots and tabs Cracks Heat damage Thickness 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. Intermediate Plate On 14-inch clutches, inspect the slots for the drive pins in the intermediate or center plate. If the slots are worn, replace the plate. On 151/2-inch clutches, inspect the tabs on the outer edge of the intermediate plate and if they are worn or damaged, replace the plate. Inspect the center plate for wear or damage. Make sure the plate is not cracked. Heat discoloration is a normal condition. The heat discoloration can be removed with an emery cloth. If heat discoloration cannot be removed, replace the center plate. Continue to check the center plate on each side of the plate according to the following procedure. Use a micrometer or caliper to measure the thickness of the center plate (Figure 14–71). If the thickness is less than the manufacturer’s specification, replace the center plate. Make sure the center plate is flat and not warped. Place a straightedge across the surface of the intermediate plate. Insert a thickness gauge under each gap that appears between the straightedge and the intermediate plate (Figure 14–72). If the gap exceeds specifications, go to step 6. Measure the runout of the intermediate plate to make sure the surface of the plate is parallel. Place the base of a dial indicator inside the center of the plate. Load the plunger of the dial indicator on the surface of the plate (Figure 14–73). Zero the dial indicator. Rotate the dial indicator one complete turn on the surface of the intermediate plate. If the reading on the dial indicator exceeds specifications, go to step 6. If either runout or warpage of the plate exceeds specifications, machine the pressure plate. Do not grind more material from the plate than necessary. Do not machine the plate smaller than minimum specification. If the plate cannot be ground flat within the minimum thickness specification, replace it.

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

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.

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

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. Solo Clutch Problems If the measurements detailed in steps 2, 3, 4, and 5 of the preceding verification procedure are out of specification, you will have to troubleshoot the cause. 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.

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. Summary • The function of a clutch is to transfer torque from the truck engine flywheel to the transmission. • 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. • 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. • 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. • 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 bearing pads. • Clutches should be checked periodically for proper adjustment and lubrication.

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. Summary • The function of a clutch is to transfer torque from the truck engine flywheel to the transmission. • 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. • 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. • 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. • 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 bearing pads. • Clutches should be checked periodically for proper adjustment and lubrication.

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. 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. 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). 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. Asbestos and nonasbestos 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.

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). 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. 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). 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. Asbestos and nonasbestos 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.

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.

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.