Abstract: A friction clutch having a known type of self-adjusting release mechanism is provided with means for preventing adjustments caused by extraneous forces rather than disc wear. In the known mechanism, adjustment is effected by a pair of ring members carried by the release mechanism, one of the ring members being rotatable relative to the other in response to disc wear to effect the compensating adjustment. The invention provides coacting means on the two ring members operable by centrifugal force to lock the members together at engine idle speed whereby adjustments induced by extraneous forces rather than actual disc wear are prevented.