A speed change gear system of the planetary type suited for applications to fluid couplings utilized upon automotive vehicles includes at least first, second, and third planetary gear sets suitably interposed between an input shaft and an output shaft, first and second clutches, and first, second, and third braking means. The first planetary gear set may include a first sun gear, a first planetary gear engaged therewith, a second planetary gear engaged with the first planetary gear, a first ring gear enmeshed with the second planetary gear, and a first carrier rotatably supporting the first and second planetary gears, while the second planetary gear set may include a second sun gear drivingly coupled to the first carrier, a third planetary gear engaged with the second sun gear, a second ring enmeshed with the third planetary gear, and a second carrier rotatably supporting the third planetary gear, and the third planetary gear set may include a third sun gear drivingly coupled to the first sun gear and the second ring gear, a fourth planetary gear interengaged with the third sun gear, a third ring gear enmeshed with the fourth planetary gear, and a third carrier rotatably supporting the fourth planetary gear and drivingly coupled to the second carrier and to the output shaft. The first clutch couples or uncouples the input shaft to or from the first sun gear, the second ring gear and the third sun gear, while the second clutch couples or uncouples the input shaft to or from the first carrier and the second sun gear. The first brake is capable of locking the first carrier and the second sun gear to the gear casing while the second brake is capable of locking the first ring gear to the casing and the third brake is capable of locking the third ring gear to the casing.