Abstract: A hydraulic dynamometer which includes a housing defining an interior working compartment and within which an input shaft is journalled. A rotor having a rotor face is mounted on the input shaft for rotation about a shaft axis. A stator is provided in the housing adjacent to the rotor and has a stator face spaced-apart from and facing the rotor face to define a rotor-stator clearance space therebetween. The rotor face has a plurality of rotor pockets and the stator face has a plurality of stator pockets which, when the interior compartment is supplied with liquid, interact with the liquid to brake the rotation of the rotor. Liquid supply passageways are provided so that liquid is supplied into the rotor pockets and is discharged from the stator pockets. A mechanism is provided to adjust the rotor-stator clearance space to adjust the operating characteristics of the dynamometer.