Abstract: A transmission coupling 1 for location between an electric motor 2 and a gearbox 3, comprises a rigid housing 4, an input shaft 5 rotatably supported within the housing 4, an output shaft 6 also rotatably supported within the housing 4 and connectable to the input shaft 5 by operation of a hydraulically actuated, multi-plate clutch 11, the output shaft 6 also carrying some elements of a multi-plate brake 22, other elements being carried by the housing 4, the brake 22 being spring loaded into operative position and hydraulically displaceable into a non-operative position, a constant pressure pump 31 to provide hydraulic pressure fluid to effect operation of the clutch 11 and brake 22, in accordance with the fluid volume demanded by clutch and brake operation, the pump volume output automatically being adjusted in response to such demand, and at least one control valve 35 to control the flow of the hydraulic fluid to the working circuit 39.