A torque modulating coupling device for operatively linking two shafts has a clutch and a piston disposed in a case. The piston selectively applies force to the clutch in response to hydraulic pressure, and a keyed feature adapted to couple with a corresponding keyed feature associated with at least one of the shafts. The coupling device can be formed with two cases that form an enclosure for the clutch and the piston, trapping the piston forces between the cases. This embodiment allows the device to also act as an axle housing cover. In another embodiment, the case is designed to bolt directly to an axle housing cover, trapping piston forces between the case and the cover.