Abstract: A control mechanism for a planetary overdrive gear mechanism for an automatic transmission which utilizes a double-acting one-way clutch with a clutch controller to immobilize the cage for the one-way clutch to allow inner and outer races to rotate relative to one another and a brake mechanism for the inner race of the clutch which is integral with the sun gear of the gear mechanism. The control mechanism includes a servomotor to activate the controller, a servomotor to operate the brake mechanism, a shift valve responsive to vehicle speed and throttle position to actuate the servomotors, and an interlock activated by the controller servomotor operative to prevent fluid actuation of the brake servomotor.