Abstract: Disclosed is a multiple, wet, friction disc brake adapted for use as a retarder in an unshown drivetrain of a land vehicle. The retarder includes a non-rotating outer housing, a centrally disposed drive shaft extending through the housing and rotatably supported therein by bearings, a plurality of axially moveable stator and rotor brake discs concentrically disposed about the shaft and alternately secured against rotation relative to the non-rotating housing and the shaft, a fluid actuated piston for squeezing the discs together, passage means defined by a portion of the non-rotating housing disposed about the outer periphery of the stator and rotor discs for introducing a pressurized cooling liquid to the outer periphery of the stator and rotor discs and flow grooves formed in the friction sides of the stator discs for the flow of the pressurized cooling liquid radially inward through the grooves.