An automotive vehicle has wheels on primary and secondary axles to which power from a motor and transmission is delivered through a transfer case. The transfer case apportions the torque between the primary and secondary axles to best suit the conditions under which the vehicle operates. The torque for the primary axle passes through the transfer case without experiencing slippage. The torque for the secondary axle is extracted at a torque bias coupling which includes a magnetic particle clutch and planetary gear set organized such that two paths exist through the coupling--one a clutch path in which slippage occurs and the other a mechanical path in which no slippage occurs. Most of the extracted torque passes through the mechanical path, but the magnetic particle clutch controls the amount of the torque extracted by the coupling. That coupling dissipates power as a consequence of the slippage in it, and a controller monitors the operation of the clutch to insure that the power dissipation, which manifests itself as heat, does not exceed prescribed limits.