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SACHS Workshop tip:
Clutch Doesn't Disengage.
General note
Our useful tips provide only an overview. The installation instructions and operating instructions provided by the vehicle manufacturer and the warning and safety instructions contained therein must be observed! All work must be performed by a trained professional. The pictures used and the procedure described in our tips are examples and may vary depending on the vehicle manufacturer and axle design.
Causes
If the clutch does no longer disengage, the problem is not necessarily damage to the clutch. Frequent causes why the clutch doesn’t disengage correctly include faults in the release system (clutch release bearing, slave cylinder, clutch lever), a jammed pilot bearing, or non-compliance with important installation requirements.
Check:
Were all check points observed during installation? See the SACHS workshop tip: Installing clutches
Worn components in the release system?
Cables, hydraulics, pivot points
Correct setting?
Lateral run-out of the clutch disk too large
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.
Excessive lateral runout of the clutch disk
Excessive lateral runout of the clutch disk
Corrosion on hub spline
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.
Fretting corrosion on hub spline
Fretting corrosion on hub spline
Hub spline damaged
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
Hub spline damaged
Hub spline damaged
Clutch disk "dished"
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.
Clutch disk "dished" (arched)
Clutch disk "dished" (arched)
Cushion springs or driving plate fractured
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.
Cushion springs or driving plate fractured
Cushion springs or driving plate fractured
Hub spline worn / burr formation
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.
Hub spline worn / burr formation
Hub spline worn / burr formation
Burst speed exceeded: facing breaks off
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.
Excessive roll speed for facings
Excessive roll speed for facings
Torsional damper destroyed by overloading
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.
Torsional damper destroyed by overloading
Torsional damper destroyed by overloading
Tangential leaf springs bent or deformed
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.
Tangential leaf springs deformed
Tangential leaf springs deformed
Diaphragm spring contacts torsional damper during release
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.
Diaphragm spring contacts torsional damper during release
Diaphragm spring contacts torsional damper during release
Diaphragm spring tips worn
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.
Diaphragm spring tips ground off
Diaphragm spring tips ground off
Extreme overheating: pressure plate fractured
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.
Pressure plate fractured
Pressure plate fractured
Related SACHS tools
SACHS Lateral Run-Out Testers for Passenger Cars and Trucks
SACHS offers lateral run-out testers for clutch discs with diameters of up to and starting from 240 mm, depending on whether passenger car or truck clutches need to be tested.
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