Tech Tips for Slipping Transmission

Slipping is one of the most common clutch problems. Slipping can occur right after installation or after years of service. A clutch slipping condition on a manual transmission equipped vehicle will manifest itself as excessive RPMs in the engine, but lack of acceleration.

There are 3 primary causes of slipping:

1. Oil leaks, over lubricated input shaft causing contaminated friction material
2. Misadjusted, binding, or worn release system, or blocked master cylinder compensation port.
3. Improperly machined flywheel.

Listed below are diagnoses of some different reasons for slipping:

• Contaminated friction material can contribute to a slipping condition caused by the loss of the material's coefficient of friction. 

Common causes of contamination include: over-lubricated input shaft splines, leaking engine rear main seals, and transmission input shaft seals. Inspect friction material for contamination. 

• If a vehicle has a hydraulic or manual cable release system, it is important to inspect for a binding condition. A release cable may be worn, stretched, or kinked. 

If you are working with a hydraulic release system, there may be issues with the slave cylinder internally. These can include deteriorated seals, o-rings, and hose. The master cylinder may also have a blocked compensation port. This would cause the clutch to remain partially disengaged. These examples can also cause unsmooth pedal travel. Be sure to properly inspect and test the release system on the vehicle.

• Another reason for slipping is improper step and cup dimensions after a flywheel has been machined. This would cause a "thick disc condition." A thick disc condition is a flywheel step that is too tall, or a flywheel cup that is too shallow. Due to the characteristics of the diaphragm spring the clamp load will be diminished, leading to a slipping condition. 

Remember to pay attention to OE flywheel specifications.