Abstract: An overdrive transmission for a motor vehicle has a housing with a rotatably mounted driving shaft and a rotatably mounted driven shaft. A planetary gear device is used to transmit power from the driving shaft to the driven shaft. In two of the illustrated embodiments, when the transmission is in the direct drive mode the planet gear carrier of the planet gear device is allowed to rotate and is engaged with the driven shaft by a clutch for power transmission at a 1:1 ratio, and when in the overdrive mode the planet gear carrier is prevented from rotation by another clutch and is disengaged from the driven shaft for power transmission to the driven shaft through the planetary gears of the planetary gear device at an increased gear ratio.