Flywheel and Self Adjusting Clutch (SAC)
The M52 TU uses the dual mass flywheel with the self adjusting clutch introduced on the E39.
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.
To check the clutch disc thickness the clutch must be removed. The pressure plate of the SAC configuration incorporates an additional "wedge" ring that rotates as the disc wears. As the ring rotates (1/2" total rotation distance) its wedges push the pressure plate disc forward to compensate for the wear of the clutch disc.
When 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.