Normal wear is the most likely cause of slipping if the disc is worn down to the rivets and the clutch has high mileage. If a newly installed clutch is slipping, the most likely causes are oil or grease contamination, incorrect release system adjustment or improper flywheel machining of a stepped or cupped flywheel.

Slipping Diagnostic Procedure
Set the emergency brake and start the engine. Put the transmission in high gear and slowly release the clutch pedal.

	Engine immediately stalls: clutch is not slipping
	Engine continues to run with clutch fully engaged: clutch is slipping excessively
	Engine slows but continues to run: the clutch is slipping partially

Dual-mass Flywheels
If the vehicle is equipped with a dual-mass flywheel, the flywheel may be the cause of the slipping. Carefully examine the old clutch to rule out the flywheel as the source of the slipping. Indications include heat marks on the pressure plate, disintegrated disc friction material and contamination of the friction material from external leaks. If these symptoms are not evident, install a new flywheel.

Causes of Slipping

External
	Incorrect release system adjustment
	Defective, worn or binding release system components
	Blocked master cylinder port
	Binding slave cylinder
	Defective cable self-adjuster

Internal
	Worn disc
	Oil leaks or excessive lubrication
	Improper flywheel machining
	Misalignment of the release bearing
	Worn dual-mass flywheel