The hydraulic piston (1) constitutes a hydraulic chamber (5) with a cylinder (4) and has a cylindrical body (6) connected—from the side of the chamber (5)—by a link-stop valve (3) to a cooling and lubricating gasket valve (2) which is passed right through by a flow calibration opening (27), the valve (2) being able to move in longitudinal translation over a short stroke with respect to the body (6) or to be held at a distance from the body (6) by the valve link-stop (3), a valve return spring (30) tending to move the valve (2) away from the cylindrical body (6).