No clutch will last forever. The facings on the clutch disc wear as the miles accumulate. The clutch pressure plate and flywheel can become scored, worn, warped or cracked from all the heat and friction generated by the clutch. A perfectly good clutch also can be ruined by oil contamination; the cable or hydraulic linkage can fail, or the release bearing, pilot bearing/bushing or fork can wear out and prevent the clutch from working properly.
Slipping will be most noticeable when the engine is under load, as when the vehicle is moving at low speed in a high gear, when going up a hill, overtaking another vehicle or when towing a trailer.
Chattering is a grabbing or jerking condition that occurs when the clutch is engaged. It is often caused by oil or grease on the clutch linings, but it also can be caused by burned or glazed linings, warped or grooved flywheel, missing flywheel dowel pins, worn pilot bearing/bushing, worn bearing retainer, worn or damaged clutch disc or input shaft splines, bent or broken drive straps on the clutch, bent or distorted clutch disc, loose clutch cover or missing flywheel dowel pins.
If the clutch does not release completely when the clutch pedal is fully depressed, the disc will continue to turn the input shaft. This may prevent moving from neutral into gear, cause grinding when the gears are changed or cause the engine to stall when coming to a stop.
Other things that can cause the clutch to drag or not release include heavy gear oil in the transmission that is too thick for cold weather, defective or worn clutch pedal bushings or brackets, or flexing in the firewall or any release component attachment point.
