Abstract: An overdrive mechanism disposed between a torque converter and change gear mechanism of an automatic transmission and responsive to the change gear mechanism. An input shaft to the change gear mechanism consists of two sections that are coupled by a clutch during normal power transmission. The driving section of the input shaft is connected to the turbine runner of the torque converter. A planetary gear train has a carrier operatively responsive to the pump impeller of the torque converter and a sun gear controlled by an overdrive brake. When the brake locks the sun gear against rotation during overdrive, the ring gear of the planetary gear train is rotated by the pump impeller and drives the second section of the input shaft through the clutch. The clutch is disengaged from the driving section of the input shaft during overdrive, thus by-passing power transmission from the turbine runner of the torque converter to the changer gear mechanism.