Master Cylinder and Slave Cylinder

Master Cylinder and Slave Cylinder

• Before replacing the master cylinder or slave cylinder on the assumption that it is faulty, first perform a function check.

• If slave cylinder is removed from transmission with pipe/hose assembly still attached, make sure you do not press clutch pedal. Otherwise, the piston will be pressed out of the slave cylinder and be destroyed.

• After installing the slave cylinder, carefully press the clutch pedal. If you feel an unusually strong resistance when depressing the clutch pedal, you must not press it down further. The push rod of the slave cylinder is likely to have been guided past the clutch release lever. The slave cylinder would then be destroyed once pedal force exceeds approximately 300 N.

Function check for master cylinder and slave cylinder

Before you replace the clutch master or slave cylinder you must - in the case of the following malfunctions - first carry out the appropriate checks.

Noises when operating the clutch:

• First check the over center spring/clutch pedal switch for noise.

• If you hear a noise, remove over center spring and repeat check.

• Replace relevant component.

After releasing clutch pedal it still remains depressed / does not return to its initial position.

• Check whether clutch pedal returns all the way to its initial position, thereby uncovering the ventilation opening in the master cylinder.

• The ventilation opening must be uncovered, otherwise permanent self ventilation for the hydraulic clutch system cannot function.

• The self ventilation function of the clutch system can be impaired if the footwell trim or foot mats get trapped, if the clutch pedal switch jams or if the driver rests his foot on the clutch pedal for long periods of time.

Check the complete hydraulic system for external or internal leaks.

• Check brake fluid level in brake fluid reservoir.

• Check master and slave cylinder as well as the line-hose assembly including connecting points for external leaks (visual check).

• If you identify any leaks you must replace the leaking component.

• Bleed clutch system, refer to => [ Clutch Hydraulic System Bleeding ] Clutch Hydraulic System Bleeding.

High pedal force:

• Clutch plate is worn (except for Self Adjusting Clutch (SAC))

• Mechanically faulty pressure plate/clutch plate. Refer to => [ Clutch General Repair Information ] Procedures.

Pedal forces:

Conventional clutch:

- Clutch lining when new: approximately 115 N

- Clutch lining at wear limit: approximately 160 N

SAC clutch:

- Approx. 140 N higher for complete service life of the clutch

Clutch does not disengage or does not disengage fully:

• Air in hydraulic system: bleed clutch system, refer to => [ Clutch Hydraulic System Bleeding ] Clutch Hydraulic System Bleeding, and check hydraulic system for external and internal leaks.

• Clutch plate does not run smoothly on input shaft splines

• Needle bearing in flywheel (centering bearing for input shaft) faulty, replace needle bearing.

• Foreign body in clutch system

• Mechanically faulty pressure plate/clutch plate. Refer to => [ Clutch General Repair Information ] Procedures.

• Wrong components used or components omitted when performing repair work (e.g. intermediate plate).