Clutch: Description and Operation

SELF ADJUSTING CLUTCH (SAC)












The 1997 E39 540i Sport is equipped with the new self adjusting clutch (SAC). This clutch will also be phased into production on the 528i in September 97 production.

The SAC is designed to extend the service life of the clutch disc while keeping the pivot range of the diaphragm spring consistent throughout its service life.

It is no longer possible to check the thickness of the disc by removing the slave cylinder. The clutch must be removed to check the disc thickness. The pressure plate of the SAC configuration incorporates an additional "wedge" ring that rotates as the disc wears. As the ring slowly rotates (1/2" total rotation distance) it's wedges push the pressure plate disc forward to compensate for the wear of the clutch disc.

If a SAC pressure plate is removed it must be reset to the "new" position before installing it into the vehicle. Using a new special tool, the wedge ring (1) is rotated back under the pressure of the spring (2) to the "new" reference line on the pressure plate.


CAUTION: A replacement pressure plate is received with a shipping "star lock". This is to be removed after installation. SAC service and replacement procedures are different and require new special tools.