Abstract: A disc brake unit comprises a disc assembly of interleaved rotor discs and stator discs that are normally spring in one direction biased to a brake engaged condition. A hydraulically operated first piston engages a stator disc at one end of the unit to move it axially in opposition to the spring bias to release the pressure between the discs and thus release the brake. A non-rotatable stop adapted to contact only one intermediate stator disc is provided to prevent movement of the intermediate disc in a direction opposite to the one direction. A second piston engages a stator disc at the opposite end of the unit for moving the rotor and stator discs on one side of a stop into engagement with each other and applies a modulated force to said rotor and stator discs while the first power piston is in position to oppose the spring bias, to thereby apply slip braking torque to the output shaft.