The illustrated two-speed accessory drive transmission includes centrifugal clutch shoes and a planetary friction unit, with spring means for urging the shoes into frictional driving contact with a clutch drum and thereby actuating the planetary unit during low engine speeds for driving the output member in overdrive, and a one-way clutch for interconnecting the output and input in a direct drive relationship upon disengagement of the shoes from the clutch drum under the action of centrifugal force, with a pin or roller mounted between an input member and a ramp formed on the clutch shoes to control disengagement of the clutch at a first predetermined speed and the reengagement thereof at a lower predetermined speed than the first predetermined speed, in both instances without undue slippage.