Abstract: A mechanical drive assembly includes driving and driven gear members with an internally splined coupling sleeve for engagement with said members. The sleeve includes a locking cam carried internally and being selectively actuable to move the sleeve between coupling-engaged and coupling-disengaged positions. The axis of rotation of the cam is offset from the central axis thereof whereby, when the cam is rotated through 180.degree. from the coupling-engaged position, the sleeve is moved forceably away from the driving member. Such movement of the sleeve is effected either by direct engagement of the cam face upon the driving gear member or by engagement of a cam follower on the driven gear member with a cam track.