Abstract: A fluid friction clutch comprising a rotatable assembly comprising a clutch housing member and a clutch cover member defining a working chamber therein, the working chamber being connected with a working fluid reservoir, valve lever means in said reservoir for controlling the admission of working fluid from the reservoir to the working chamber where it serves to transfer torque between a rotatable disc disposed in the working chamber and said rotatable assembly, means for actuating the valve lever means comprising a pressure chamber formed from a pressure chamber housing and a flexible membrane carrying a pressure plate which directly engages the valve lever means, the pressure chamber housing and membrane being joined to the rotatable assembly to rotate therewith, and means for introducing a pressure medium such as compressed air into said pressure chamber to actuate the valve lever means and control the admission of working fluid from the reservoir into the working chamber, said pressure medium introducing