Abstract: A reversible power transmission unit comprising a housing and a cam block rotatably mounted in the housing and a pumping mechanism associated with opposed inclined surfaces of the cam block. A common shaft is rotatably mounted in the cam block and has its ends extending beyond the cam block. Each pumping mechanism includes a cylinder barrel mounted on the shaft for rotation with the shaft and having a plurality of cylinders with pistons slidable therein and operatively associated with a surface of the cam block. Each cylinder has a port opening to a valve plate provided with inlet and outlet ports in communication with inlet and outlet passages at each end of the housing. When one of the pumping mechanisms is operated as a motor, it drives the other pumping mechanism as a pump.