A clutch slip happens when the driven disk fails to rotate at the normal speed when the clutch is fully engaged. This result is the clutch's pressure plate failing to hold the disc firmly against the front of the flywheel.

Causes

Grease and oil on the disc can create a clutch slip. This problem, however, is not caused with the clutch-release mechanism; the problem is usually inside the clutch. A broken engine mount is another cause of slippage; it allows the clutch to move.

Signs

If the clutch pedal is beginning to feel rigid and demands a lot more power when pressing on it, it is a sign of a clutch malfunction. One of the most noticeable signs is if adjustment of the clutch pedal creates less pedal "free play."

Prevention/Solution

The clutch linkage allows enough change to balance the lining to come close to the rivet heads. It prevents damage to the pressure plate by fastening the wearing grooves in the surfaces. Take off the inspection cover on the clutch housing and check the disc. Binding linkage also inhibits the pressure plate from applying total pressure amongst the disc, causing it to slip.

Testing

Place on the emergency brake and start the engine. With the transmission on high gear, slowly drive the vehicle. A good clutch would cause the engine to instantly shut down; a bad clutch will allow the engine to continue to run.

Warning

Don't allow the clutch to clip for more than a second because it can create an exceeding amount of heat and can severely damage the pressure plate faces.

Source:

Clutch Diagnosis