Clutch repair disc pressure plate throwout bearing
No clutch will last forever. The facings on the clutch disc wear as the miles accumulate. Stop-and-go city driving with lots of shifting is obviously harder on the clutch than open highway driving. Pulling a trailer, off-roading and aggressive driving can also accelerate clutch wear.

The worst thing any driver can do is ride the clutch. Slipping the clutch excessively when starting out or when creeping along in traffic sends the temperature of the clutch soaring. If the facings get too hot, they may start to burn giving off an odor similar to burnt toast. If the clutch isn't given a chance to cool, the disc may be ruined along with the flywheel and/or pressure plate.

When the clutch disc becomes worn, the reduction in thickness may reduce the clamping force exerted by the pressure plate. Most diaphragm clutches actually exert more pressure as the disc wears due to the geometry of the spring and release mechanism. But once the disc is worn beyond a certain point, pressure starts to drop, increasing the risk of slipping under load. With older coil spring-style clutch covers, pressure drops in direct proportion to disc wear.

When a clutch starts to slip, the slippage will be most noticeable when the engine is under load, as when lugging at low speed in a high gear, when driving up a hill, when accelerating to pass another vehicle or when towing a trailer. The more the clutch slips, the hotter it gets and the more it wears. This accelerates the problem even more and may result in additional damage to the flywheel and pressure plate.

Another cause of premature clutch failure is oil contamination from a leaky rear main crankshaft seal, transmission input shaft seal or engine oil leak. Oil on the clutch facings will cause them to slip and grab unevenly. The result is typically chattering and jerking when the clutch is first engaged, and slipping when the clutch is under load.

Oftentimes, an apparent clutch problem really isn't the clutch, but the clutch linkage or something else. Many late-model vehicles have a hydraulic clutch linkage with a master cylinder attached to the clutch pedal and a slave cylinder on the bellhousing. The internal piston seals on the master and slave cylinder can develop leaks that allow a loss of pressure when the clutch pedal is depressed. This may prevent the clutch from disengaging or allow it to engage prematurely (as when sitting at a stop light with the pedal all the way in). The pedal may also feel soft and have less than normal resistance. Slave cylinders develop leaks more often than master cylinders because the slave cylinder is the lowest point in the system. Any rust or dirt in the hydraulic fluid is therefore more apt to settle in the slave cylinder where it can cause seal problems.

 DIAGNOSIS

Diagnosing clutch problems is difficult because a lot of different problems can cause the same kind of symptoms. Chattering or grabbing when the clutch is engaged can also be caused by burned or glazed linings, a warped or grooved flywheel, missing flywheel dowel pins, a worn pilot bearing/bushing, a worn bearing retainer, worn or damaged clutch disc or input shaft splines, bent or broken drive straps on the clutch, a bent or distorted clutch disc, a loose clutch cover or even missing flywheel dowel pins.

External causes of clutch chatter include loose or broken engine or transmission mounts, misalignment of the chassis and drivetrain components, worn or damaged U-joints or CV joints, a loose transmission crossmember, a worn or bent release fork, or loose rear left spring bushings or spring U-bolt nuts.

If the vehicle is equipped with a dual mass flywheel, a bad flywheel may be the cause of the slippage. Carefully examine the old clutch for heat marks on the pressure plate, disintegrated disc friction material and contamination of the friction material from external oil leaks. If no such evidence is found, the problem is the flywheel.

If a newly installed clutch is slipping, the most likely causes would be oil or grease contamination, incorrect release system adjustment, a defective cable adjuster, a blocked clutch master cylinder port or binding slave cylinder, a misaligned or improperly installed release bearing, or improper flywheel machining of a step or cup flywheel.

CLUTCH SERVICE

Replacing a clutch is a labor-intensive job because the transmission or transaxle must be separated from the engine. So, before you invest a lot of labor in a clutch job, make sure the clutch is really at fault and needs to be replaced. And if it does, be sure to inspect the entire clutch system once you've disassembled everything and have the clutch out to see if any additional parts need to be replaced. Better to do a thorough job once than a half-hearted job twice.

In high-mileage vehicles, you should probably replace the entire clutch assembly with a kit that includes a new or remanufactured clutch disc, pressure plate and release bearing - and pilot bushing if one is used.

If a low-mileage vehicle has a clutch problem, you may only have to replace the individual component that failed. It depends on the failure and what caused it. If the disc in an otherwise good clutch is contaminated with oil, replacing the disc (and repairing the oil leak) should be all that's needed to get the vehicle back on the road.

One thing to watch out for when doing clutch work is poor quality remanufactured parts. On many vehicles the height of the spring fingers and release mechanism is critical for proper clutch operation. If the clutch is not remanufactured to OEM specifications, it may not function properly or fail prematurely. So, don't take unnecessary risks to save a few extra bucks. Install quality parts from a reputable supplier who has a good track record for clutches that work and don't come back to bite you.

Another item that should also be replaced is the release cable on older vehicles with this type of linkage. On high-mileage vehicles with a hydraulic linkage, you should also recommend replacing the master clutch and slave cylinders, too, even if they are not leaking. These parts don't last forever either. If the clutch has reached the end of the road, chances are the rest of the system's components are nearing the end of their service life, too. It's better to restore the entire clutch system to like-new condition at one time than to fix one part now and maybe have to fix another part when it fails later on.

  FLYWHEEL RESURFACING

The flywheel should always be resurfaced or replaced when a clutch is changed. Oil, dirt, grease, warpage, cracks or grooves on a flywheel can cause clutch problems. So too will excessive runout. Remember to mark the index position of the flywheel before you remove it so it can be reinstalled in the same position as before. This is essential on externally balanced engines. New bolts are also recommended. Use a torque wrench to tighten to specifications.

If a flywheel is cracked or damaged or cannot be resurfaced, replacement is required.