A rotary clutch assembly for a geared power transmission mechanism comprising a friction disc clutch with driving and driven friction clutch plates, the driving plates being connected to a torque input element of the clutch assembly and the driven plates being connected to a torque output element of the clutch assembly, the clutch assembly providing a torque flow path to multiple-ratio gearing, a pressure actuator comprising first and second annular cylinder members and a movable piston member located in one of the cylinder members and cooperating with each member to define a pressure release chamber and a pressure apply chamber, the second clutch member being held axially fast on a torque input shaft for the transmission, the geometry of the cylinder members and the movable piston being sized to effect a centrifugal balance so that the clutch gain is essentially determined by the clutch commanded pressure to produce a relatively speed-independent net clutch-apply force, regardless of clutch cylinder speed.