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Clutch Life Often Depends on Habits of Vehicle Owner

There comes a time in the life of every clutch when it must be replaced. When exactly that occurs depends on the driver, what kind of driving the vehicle has been subjected to and the design life of the clutch itself. Stop-and-go city driving eats up clutches at a much faster rate than highway driving, and pulling a trailer can fry a clutch rather quickly if the stock clutch can’t handle the load.

What usually wears out first is the clutch disc. The friction linings gradually wear down as a result of heat and friction. The more often it is engaged and disengaged, the faster it wears. A driver who "rides" the clutch and allows it to slip excessively will only make matters worse. Another item that will eventually wear out is the throw-out or release bearing. Most release bearings are not designed to remain in constant contact with the fingers on the clutch diaphragm. If the linkage is too tight, the constant friction can wear out the bearing rather quickly. Bearings can also be damaged by dirt and water that get inside the clutch housing.

The clutch cover assembly is fairly durable, but it also experiences some wear as the miles accumulate. The most common wear areas are the fingers that contact the release bearing and the face of the pressure plate that presses against the clutch disc. If either are worn or damaged, the cover must be replaced when the clutch disc is replaced.

Most front-wheel-drive cars that are equipped with a manual transaxle do not have a pilot bearing or bushing in the center of the flywheel, so that’s one less item to be concerned about.

CLUTCH SYMPTOMS
• Slipping — Slipping is usually an indication that the clutch disc and/or pressure plate have reached the end of the road. Most diaphragm clutches actually exert more force against the disc as it wears down, but older coil spring clutches do not. In some instances, though, slipping is caused by linkage that’s out of adjustment. The linkage is too tight and does not allow the release bearing to return to its normal rest position after the clutch pedal has been released. The same problem can occur if the linkage is binding. Another cause of slipping may be grease or oil on the clutch linings, flywheel or pressure plate.

• Chattering and Grabbing — If the clutch chatters or grabs instead of engaging smoothly, the most likely cause is oil or grease on the clutch linings. A leaky crankshaft rear main oil seal may be the source of the unwanted oil. There could also be a leaky transmission or transaxle input shaft seal, a manifold or valve cover oil leak on the engine, binding in the clutch linkage or a broken powertrain mount. Other causes of this condition include binding or rust on the input shaft splines, broken or damaged clutch facings or pressure plate assembly, a warped clutch disc, damaged or broken damper springs in the clutch disc hub, or a collapsed marcel spring in the clutch disc.

• Dragging and Disengagement Problems — If the gears grind when shifting or the clutch fails to completely disengage when the pedal is depressed all the way to the floor, the clutch disc may be dragging against the flywheel or pressure plate. The most likely causes here would be insufficient linkage travel (check the adjustment), a damaged clutch disc (loose or warped friction linings, or a damaged or bent hub), a broken release lever on a coil spring clutch cover, binding or rust on the input shaft or a broken powertrain mount.

If you suspect the clutch disc is dragging, try this test: with the engine and transmission at normal temperature, push the clutch pedal all the way to the floor, wait five or six seconds, then shift the transaxle into reverse. If the transaxle does not shift smoothly, the clutch disc is dragging.

If the clutch fails to release at all, and there is less than the normal resistance in the pedal, the clutch cable or release fork may be broken or a linkage rod may have become disconnected. If the car has a hydraulic linkage, the fluid level in the master cylinder may be low, the piston seal in either the master or slave cylinder may have failed, or the fluid hose may be leaking. If pedal effort, free play and travel are normal, but the clutch fails to release, the clutch disc or pressure plate assembly may be damaged.

If the clutch was just replaced, the clutch disc may have been installed backwards with the wrong side facing the flywheel bolts and disc hub. Using extra washers or lock washers under the bolts may raise the bolt heads, causing them to make contact with the disc hub. Another possibility is mismatched components. Installed height is especially critical with front-wheel-drive diaphragm clutches for proper operation. If a clutch disc from one manufacturer is used with a pressure plate assembly from a different manufacturer, or the release bearing is not the correct one for the application, the release bearing may not push the clutch fingers in far enough to disengage the clutch.

• Pedal Pulsation — If the clutch pedal pulsates or vibrates when depressed, it usually indicates misalignment between the engine and transaxle or an internal clutch problem, such as a broken clutch diaphragm spring, a warped or misaligned pressure plate, or a warped or bent clutch disc.

• Clutch Noise — The conditions under which a noise is heard will help diagnose the source of the problem. If the noise only occurs when the clutch pedal is depressed, the most likely cause would be a faulty release bearing. On applications where the release bearing is in light contact with the clutch fingers all the time, the bearing may be noisy all the time or only when pressure against it increases.

Clutch noise that occurs only while the clutch is engaged (pedal up) may indicate excessive play between the splines on the clutch disc hub and input shaft, a damaged center damper in the clutch disc hub or misalignment between the engine and transaxle.

CLUTCH SERVICE
Replacing a clutch is a labor-intensive job on most FWD cars, so make sure the problem is the clutch and not the linkage. If the linkage is in good working condition, and an adjustment fails to solve the problem, it’s probably the clutch.

Clutch removal procedures vary depending on the application. On some FWD cars (certain Honda and Nissan models and Pontiac LeMans) little disassembly is required to replace the clutch. But on most FWD cars, the transaxle must first be removed before the clutch can be inspected and replaced. If so, proceed as follows:

1. Disconnect the battery.

2. Drain the cooling system and disconnect the coolant hose.

3. Disconnect the throttle linkage, fuel lines, wiring harnesses and ground straps from the engine.

4. Remove any structural supports (braces) or engine-mounted accessories that would prevent easy engine removal.

5. Connect a hoist to the engine so that it can be raised or lifted out of the engine compartment and supported.

6. Disconnect the motor mounts and supporting transaxle (if necessary).

7. Unbolt the transaxle from the engine.

8. Separate the engine from the transaxle and raise the engine.

9. Remove the clutch components from the flywheel on the engine.

If the procedure calls for removing the transaxle, do the following:

1. Disconnect the battery.

2. Remove the front wheels.

3. Remove both front hub nuts.

4. Disconnect the lower ball joints to separate the lower control arms from the steering knuckles (may not be required on some applications).

5. Remove both halfshafts.

6. Support the engine from above with a brace or hoist.

7. Disconnect the clutch and shift linkage from the transaxle.

8. Disconnect the transaxle mounts.

9. Disconnect the engine cradle or crossmember (as needed).

10. Unbolt the transaxle from the engine and lower the transaxle from the vehicle.

11. Remove the clutch components from the flywheel.

INSPECTING THE CLUTCH COMPONENTS
The clutch disc must be replaced if you see any of the following:

• Friction linings are worn down to minimum specifications or to the rivet heads;

• Linings are frayed, cracked, loose, oil soaked or burned;

• Damper springs in the hub are loose, broken or missing;

• Disc or hub is bent, warped or cracked; and/or

• Hub splines are damaged or badly corroded.

A new clutch cover and pressure plate assembly will be needed if you find:

• The friction surface of the pressure plate is warped, scored, cracked or damaged;

• Pressure plate cover is cracked, bent or damaged;

• Coil springs are weak, broken or damaged;

• Clutch release fingers are worn, bent or broken;

• Diaphragm spring is broken or damaged; and/or

• Diaphragm spring fingers are worn, bent damaged or broken.

Next, inspect the flywheel. Check the starter drive teeth for damage. If any teeth are broken or damaged, repairs should be made to assure reliable starting. If the teeth are on a separate ring gear on the flywheel, the ring gear can be replaced. Otherwise, your customer will need a new flywheel.

Check the surface of the flywheel. If any of the following are found, the flywheel will have to be resurfaced or replaced:

• Cracks, warpage, scoring grooves or other surface damage. The friction surface must be in good condition for smooth clutch operation and maximum service life;

• Runout exceeds about .005 inches (.13 mm) or vehicle manufacturer specifications. Measure runout on the face of the flywheel with dial indicator attached to the block. Position the tip of the dial indicator against the friction surface of the flywheel and rotate the flywheel one full turn; and/or

• Flywheel-to-block runout exceeds specifications. Measure flywheel-to-block runout by placing the dial indicator on the block with the top against the back inside edge of the flywheel. Rotate the flywheel one full turn. If runout exceeds specifications, the flywheel or crankshaft flange may be bent.

If the flywheel is cracked, replacement is required. However, if only the surface is worn, it can be removed and resurfaced. Resurfacing the flywheel reduces its thickness slightly, which affects the installed height of the clutch and travel of the release bearing. On some vehicles, resurfacing the flywheel may remove too much metal and cause engagement problems — so replacing the flywheel may be the only repair alternative on such applications.

Some cars have stepped or recessed flywheels where the friction surface is below the clutch cover mounting surface. This requires special resurfacing equipment to maintain the same relative dimensions between the friction surface and clutch cover mounting surface. On some General Motors vehicles, resurfacing a recessed flywheel is not recommended because the friction surface has a slight taper that cannot be reproduced by the resurfacing equipment found in most aftermarket machine shops.

If the flywheel does need to be resurfaced, remember to mark its index position relative to the crankshaft before it comes out to maintain proper engine balance and ignition timing (if the engine has a crank position sensor that reads off the flywheel).

Inspect the release bearing. It should turn smoothly. If any binding, roughness or noise is found, or if the bearing is loose, replacement is required. If the face of the bearing shows wear, scoring or other damage, don’t take a chance on it;. replace it. Also, check the release bearing fork for any damage and to make sure that it holds and supports the bearing properly. Check the pivot for wear, rust or damage.

CLUTCH INSTALLATION
Before the clutch is installed, the surface of the flywheel and pressure plate should be cleaned to remove any traces of grease or oil that may be present. Use a cleaner that does not leave a residue such as alcohol or brake cleaner.

A thin film of high-temperature grease should be applied to the splines on the transaxle input shaft and inside the clutch disc hub. Do not over-lubricate to prevent grease from splashing on the clutch disc and contaminating the linings. Other items that may also need to be greased include the sleeve on the input shaft for the release bearing and the pivot or hinge points of the release fork.

Use a pilot tool to center the clutch disc on the flywheel, then bolt the clutch cover in place using a star-pattern to tighten the bolts to specs.

Once everything is in place, the engine and transaxle can be remated. New hub nuts are recommended for FWD cars that use torque prevailing nuts. Use a torque wrench (not an impact wrench) to tighten specs. Check the lubricant level inside the transaxle before test driving the vehicle and adjust the linkage and clutch pedal free travel as needed.

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