Abstract: Apparatus for the selective engagement and disengagement of a ring gear of a gear set in which an actuator can be displaced between a first position engaging the ring gear and a second position disengaged from the ring gear selectively by a manually operable mechanical arrangement or a fluid pressure arrangement without altering or adding to the housing or control device of the gear set. The mechanical arrangement and the fluid pressure arrangements are integrated so that the operation of the actuator can be selectively achieved either by the mechanical or fluid arrangement.