Abstract: A variable displacement axial piston hydraulic pump or motor having a rotatable cylinder barrel with working pistons suitably connected for thrust engagement with the thrust face of a cradle supported for pivoted movement in one plane within a housing for the pump or motor to effect reciprocal movement of the working pistons in accordance with the tilt of the thrust face. The cradle has a rigid lever arm extending rearwardly of the face. A coupling pin is journalled in the lever arm; and a free end of the coupling pin has two flat sides fitted in an annular groove of a displacement control piston; whereby linear movement of the control piston transmitted through the coupling pin as the free end of the coupling pin slides laterally within the annular groove of the control piston to accommodate the angular movement of the cradle. And stops within the housing abut either side of the coupling pin intermediate the ends thereof to limit maximum displacement.