A hydraulic displacement unit of the axial piston fixed displacement type having a rotatable cylinder block with axially reciprocal pistons, each of which has a slipper associated with a swash surface, as defined by a thrust plate, and structure for obtaining fixed maximum clearance between the slippers and the thrust plate. This fixed maximum clearance is achieved by the use of the controlled positioning of a slipper retainer bearing relative to the surface of the thrust plate by use of a tubular member positioned within the cavity of the unit housing which is securely located and positioned by assembly of an end cap to the housing to be located between the thrust plate and the end cap. The tubular member has a series of windows at the thrust plate end thereof for receiving outwardly-extending peripheral tabs on the slipper retainer bearing to control the distance of the slipper retainer bearing from the thrust plate and with the thickness of the slipper retainer bearing, a slipper retainer, and slipper feet determining the fixed maximum clearance. The tubular member is constructed with permanently deformable fingers to take up manufacturing tolerances between components upon assembly of the unit and has provision for optional mounting of different types of spring structures acting on the slippers for urging the slippers toward the thrust plate and resisting tipping thereof.