A device for transmitting torque between two rotatable, coaxial shaft members (1, 2) in a stationary housing (4) has a clutch (11, 12) engageable to counteract differential rotational speed between the shaft members. A hydraulic clutch piston (14) is arranged to engage the clutch, and a hydraulic pump arrangement (1', 18 - 21, 11'', 14 - 17), driven by the speed differential between the two shaft members, creates a hydraulic pressure on the clutch piston. The hydraulic pump arrangement includes a supply piston (18) and the clutch piston. Rollers (17, 21) are rotatable with one of the shaft members (2) and engage the other of the shaft members (1) via cams (1', 11''), which are angularly offset in relation to each other, so as to impart to the pistons a reciprocating movement at the differential rotational speed between the shaft members. A hydraulic line system (25, 27, 29, 31) connects a cylinder (23) at the supply piston on one hand with the tank (24) via a check valve (26) and on the other hand - via a line (27) with a check valve (28) - with an outlet line (31) and connects a cylinder (30) at the clutch piston (14) with the outlet line.