Clutch Doesn’t Disengage

Cause:

• Deformation during transport or installation
• Lateral run-out of approx. 0.5 mm significantly exceeded

Consequence:

The specified lift on the pressure plate is no longer sufficient to ensure full disengagement.

Comment:

Always check clutch disks for lateral runout before installation.

Cause:

• Not or not correctly greased during installation
• Contamination of the friction surfaces due to incorrect handling

Consequence:

Clutch disk fails to slide freely on transmission shaft, jams. Clutch facing still contacts friction surface on flywheel.

Comment:

Clutch grab may be noticeable in early stages. Always use high-performance lubricant, SACHS No. 4200 080 050.

Cause:

• Transmission shaft and clutch hub forced together during installation
• Excessive angular movement during transmission installation

Consequence:

The clutch disengages badly because the clutch disk jams instead of sliding on the input shaft.

Comment:

• Center the clutch disk - using the right tools - during installation
• Do not move the transmission too far up and down or laterally during mounting

Cause:

• Input shaft jammed against clutch disk hub during installation
• Deformation due to severe overheating (blue discoloration of metal components)

Consequence:

The clutch does no longer disengage because the prescribed lift on the pressure plate is no longer sufficient.

Cause:

• Engine or transmission dropped with the input shaft still in the clutch disk hub, fracture due to lever effect
• Parallel or angular offset

Consequence:

Clutch disk lateral run-out too large.

Comment

• Do not move the transmission too far up and down or laterally during mounting.
• Only lower transmission during disassembly and assembly when the input shaft is not inside the clutch disk.

Cause:

• Clutch bell housing and crankcase flange not centered, wobble motion due to angular or parallel offset
• Pilot bearing missing
• Transmission input shaft has excessive play or is not guided

Consequence:

• Hub jammed or tilted on transmission input shaft
• Hub spline heavily worn

Comment:

Can also cause noise.

Cause:

• Driving at high roll speeds in low gear with the clutch pedal depressed, clutch disk exceeds maximum permissible speed (burst speed)
• Selecting the wrong (too low) gear when downshifting

Consequence:

Facing debris gets stuck in the flywheel or in the clutch pressure plate housing.

Comment:

The engine is not involved at all! Facing burst speed is higher than the maximum engine speed. Overheated facings may burst earlier.

Cause:

• Low-revving driving style, driving at low speeds in high gear and full throttle
• Extreme irregular engine operation
• Worn joints in the driveline

Consequence:

Fragments are thrown outwards and get stuck in the facings.

Cause:

• Extreme thrust load due to incorrect shifting
• Improper towing maneuvers
• Operational errors on the roller test stand
• Play in the driveline
• Bent during installation
• Transport damage

Consequence:

Insufficient pressure plate lift. The clutch doesn’t fully disengage.

Cause:

• Permissible release travel exceeded
• Incorrect clutch disk installed
• Clutch disk installed wrong way round

Consequence:

Diaphragm spring drives clutch disk

Comment:

Also causes noise.

Cause:

• Clutch releaser preload too low
• Clutch actuation system worn
• Guide tube worn or bent
• Engine and transmission not precisely centered

Consequence:

Continuous off-center clutch releaser contact with the diaphragm spring tips exceeding the self-centering capacity. These relative motions increase wear on all mechanical operating elements. Clutch does not disengage properly. This also applies to the release levers.

Cause:

• Clutch permitted to slip constantly
• Insufficient downforce of the clutch pressure plate
• Problems with the release system, e.g., stiffness
• Contamination with oil or grease
• Excessive flywheel thickness

Consequence:

Insufficient pressure plate lift.

Comment:

Extreme overheating can cause irreversible dishing of the pressure plate leading to disengagement problems.