Abstract: An annular actuator for moving a member axially to couple and un couple a drive member with a driven member of a vehicle drive train. The actuator encircles the drive and driven member. The actuator has a housing to which a diaphragm is mounted. A spring biases the diaphragm to move in one axial direction and withdrawal of air forces the diaphragm to move in the opposite axial direction. A shifting fork coupled to the diaphragm moves a clutch ring in the one axial direction to be coupled with only one of the drive and driven members and is coupled with both the drive and driven members when moved in the opposite direction. The actuator defines a sealed chamber that is totally non-rotatable with relative movement occurring between the shifting fork and the clutch ring.