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We've gathered the following collection of tips and information that can help make your next clutch repair job easier, safer and deliver the optimum clutch performance.
Attention to detail, thorough examination and replacement of all worn clutch system components can eliminate immediate off-the-lift problems and prevent premature clutch failure. Always follow manufacturers' guidelines for clutch removal and replacement.
(1) Clutch assembly
(2) Disc assembly
(5) Pilot bearing/bushing
(6) Rear main seal
(7) Transmission input shaft
(8) Bearing retainer
(9) Release bearing
(11) Input shaft seal
The clutch, disc, release bearing and pilot bearing or bushing in your LuK RepSet may not be identical in appearance to the components removed from the vehicle. If the LuK RepSet part number is the correct one for the application, you can be sure the components will fit and function properly, despite differences in appearance.
In the case of release bearings that appear dissimilar, you can measure three dimensions on each of the bearings and compare the results. The dimensions should be identical, indicating they are fully interchangeable.
Use a caliper to measure the following dimensions on the new bearing and the one you remove from the vehicle.
1. Bearing Contact Diameter (DIM #1). The bearing contact surface is the area that contacts the diaphragm spring fingers. It is also called the face. Measure from the center of the face on one side to the center directly across on the other side.
2. Inside Diameter (DIM #2). This is the measure of the center of the bearing.
3. Height. This dimension is not necessarily the overall height of the bearing. On a bearing assembly, measure from the face of the bearing to the fork contact point at the collar (DIM #3a). In the case of a bearing only, measure from the face of the bearing to the bearing collar contact point (DIM #3b).
Angular-contact bearings, found in hydraulic release systems and self-adjusting cable systems, are in constant contact with the diaphragm spring fingers. Self-centering bearings are designed to compensate for slight misalignment between the engine and transmission. It is normal for these bearings to be "off center" until they contact the diaphragm spring fingers.
Organize teardown procedures to keep track of parts and speed installation. Many of the procedures you use during removal of the old clutch can prevent errors. As you remove the old clutch, note all bolt locations. Bell housing bolts may have different lengths, diameters and thread pitches. If any of the bell housing bolts are used to attach a ground cable to the transmission, mark the bolt and its location. Clean and check all bolts for thread damage.
If the crankshaft flange bolt pattern is symmetrical, mark the relationship of the flywheel to the crankshaft mounting flange to eliminate a balance problem. If the pattern is asymmetrical, the flywheel will only go on one way.
Inspect all release system components and replace any that are worn. This includes the clutch cable, pivot bushings, fork, fork pivot ball, and hydraulic slave and master cylinders. This inspection is especially important if the vehicle has high mileage and the owner experienced release problems.
Examine other vehicle components that have worn during the service life of the clutch, including the halfshaft, carrier bearings, universal joints, driveshaft components and powertrain mounts. Driveline components and engine and transmission seals that were new when the original clutch was installed have been subjected to heat and vibration. Worn driveline components are a common cause of vibration. They must be replaced to prevent problems with the new clutch.
Even if inspection does not indicate leaks, replace rear main bearing and transmission input shaft seals on high mileage vehicles. It is not realistic to expect high mileage seals to continue sealing through the service life of several clutches.
Clutches create abrasive debris as they wear. This powdery abrasive penetrates all the components inside the bell housing. If these components are not properly cleaned and lubricated, they can cause release or engagement problems. Look for signs of oil contamination inside the bell housing. If found, locate and repair the source.
Examine the input shaft splines and bearing retainer for wear and damage that will limit disc travel and cause release and engagement problems. If the bearing retainer is damaged or distorted, replace it. Repair sleeves are available for some designs in which the bearing retainer is a part of the transmission housing. The repair sleeves enlarge the diameter of the bearing retainer and must be used with a release bearing with a larger inside diameter.
Internal slave cylinders, also called concentric slave cylinders, are prone to early failure due to the conditions inside the bell housing. Always replace internal slave cylinders during clutch installation to prevent premature failure. Internal slave cylinders require special handling to ensure proper operation.
Inspect and clean the bell housing and engine block mating surfaces. Make sure the locator dowels and dowel holes are clean to eliminate installation problems and prevent misalignment.
Proper resurfacing of the flywheel is critical to clutch operation. The flywheel must be resurfaced or replaced; failure to do so will void the warranty of the clutch set.
Increasingly, original equipment clutch systems are designed without allowance for flywheel resurfacing. If manufacturers' specifications indicate this, the flywheel cannot be resurfaced and must be replaced during clutch installation to avoid contact between the disc and flywheel, and catastrophic failure.
When resurfacing a stepped or cupped flywheel, be sure to machine the contact surfaces by equal amounts to maintain specified tolerances. Do not assume the existing dimensions are correct, particularly if there were release or engagement problems. If the flywheel shows signs of extreme overheating and deep scoring, it must be replaced.
Flywheel cup and step dimensions are available in our online catalog, by searching under your vehicle application, selecting a clutch set and clicking "details."
Clean the mating surface between the crankshaft flange and flywheel mounting surface. In some applications, flywheel bolts require the use of a special thread sealer to prevent oil leaks. Refer to manufacturers' specifications for thread sealer and torque specifications. If the flywheel has been handled by grease- or oil-covered hands, clean it with an alcohol-based cleaner.
Due to their design, LuK does not recommend resurfacing dual-mass flywheels. For some applications LuK offers solid flywheel replacements for dual-mass designs. Engineered as bolt-in replacements, LuK RepSet and solid flywheel replacement options provide increased torque capacity. Many include larger diameter clutches than the original equipment.
The release bearing fork/combination on many General Motors applications makes it very easy to install the parts incorrectly with the leaf spring clip of the fork above the bearing collar. Improper installation will cause slipping, hard pedal and release problems. Ensure the leaf spring is installed under the bearing collar.
If you are replacing a coil-spring clutch with a diaphragm-spring clutch, remember to remove the over-center or release-assist springs. Designed to reduce the higher pedal effort associated with coil-spring clutches, over-center springs may overcompensate when a diaphragm-spring clutch is installed. This can result in a very soft pedal and, in some cases, a pedal that will go to the floor and stay there.
Incorrect installation of the disc will result in interference between the disc and flywheel. Many LuK discs are marked to indicate the side that faces the flywheel.
If you are installing a disc with cerametallic rather than organic friction material, advise the vehicle owner that this friction surface may be characterized by abrupt engagement and some clutch chatter.
Clean the contact surface of the pressure plate with an alcohol-based cleaner. Use an alignment tool to properly center the disc and install the clutch. Tighten the bolts by hand in a criss-cross, star pattern, drawing them down gradually. This applies stress to the clutch evenly. Never use an air-powered wrench; it will damage the clutch, causing chatter and no release. Torque all bolts to manufacturers' specifications.
Never lubricate conventional ball bearing pilots. A small amount of bearing grease can be used on needle bearing pilots; however, never use grease on sintered bronze bushings. The material in the bushing is designed to gradually release lubrication through small pores. Use a few drops of SAE 30-weight motor oil as an aid to installation.
Lubricate the input shaft splines with a very small amount of high-temperature grease. Then test fit the disc on the splines to distribute a thin film of grease. Make sure it moves freely. Remove the disc and wipe away any excess grease.
Lubricate the bearing retainer with a very light film of high-temperature grease applied to the sliding surface. If the inner diameter of the release bearing is made of nylon, do not lubricate.
Support the transmission with a jack, and keep the input shaft properly aligned with the disc hub as the transmission is reinstalled. If the transmission input shaft will not engage the disc, check the alignment of the transmission and engine. Never force the transmission into the disc or use the bell housing bolts to pull a transmission into place if it won't fully seat against the engine.
Once the shaft is engaged in the disc, keep the transmission jack in place until the bell housing bolts and cross member or cradle bolts are tightened. If the jack is removed before the transmission is properly bolted to the engine, the weight of the transmission on the input shaft will bend the disc, resulting in chatter or no release.
Replace the clutch cable with every clutch installation. In systems with self-adjusting cables, always check for correct operation of the self-adjusting mechanism. Adjust the cable or mechanical linkage free play to the manufacturer's specifications. Then operate the clutch several times to make sure that the cable housing is firmly seated in its mounts. Test drive the vehicle and make any final free-play adjustments.
Examine the master and slave cylinders for leaks. On vehicles equipped with hydraulic release systems, replace the hydraulic fluid. Follow manufacturers' recommendations for fluid type and use fresh fluid from a sealed container to avoid damage to the seals.
The degree of difficulty in bleeding a hydraulic system often depends on the angle at which the hydraulic components are mounted. LuK offers a line of reverse fluid injection bleeder tools. With one tool, one technician can bleed the hydraulic system quickly and efficiently.
For slave cylinders without bleed screws to purge air, follow the procedures below for proper bleeding. If the slave cylinder has a gold allen screw, do not remove or loosen it. The screw set is not designed for bleeding.
1. Push the slave cylinder pushrod inward and disconnect both bands of the retaining strap to enable the pushrod to fully extend. Do not cut or discard the retaining strap.
2. Tilt the slave cylinder at a 45-degree angle. The master cylinder line port should be facing upward with the port at the high end of the slave. Fill the slave cylinder with fresh, clean brake fluid.
3. Insert the master cylinder line into the slave cylinder port. Lubricate the enclosed o-ring with brake fluid and insert the retaining pin.
4. Hold the slave cylinder vertically with the pushrod facing the ground. If this is not possible due to the master cylinder line, position the slave as far vertically as possible without putting excessive load on the master cylinder line. The slave cylinder must be lower than the master cylinder.
5. Remove the master cylinder reservoir cap.
6. Slowly push the slave cylinder pushrod into the slave approximately one inch, watching for air bubbles in the master cylinder reservoir. Air in the release system should be purged after 10 to 15 strokes of the slave cylinder pushrod.
7. After all air is purged from the system, slowly push the slave cylinder pushrod back into the slave and reconnect the two bands of the retaining strap.
8. Install the slave cylinder with the retaining strap in place. The retaining strap will break free with the first stroke of the pedal.
Note: The plastic cover over the end of the pushrod must be retained; it acts as a lubricant between the pushrod and the fork. Removing the cover can cause a no release condition.