Abstract: An on-demand four wheel drive system for a vehicle having a front drive train, a rear drive train, and a transfer case. The system includes a sensor system operable to detect the speed of the front drive train and the speed of the rear drive train. The system also includes a controller operable to cause the transfer case to supply input torque to the front drive train and the rear drive train when the sensor system detects that the speed of the rear drive train exceeds the speed of the front drive train by a predetermined amount. The controller is further operable to cause the transfer case to limit the amount of input torque supplied to the front drive train when the sensor system detects that the speed of the front drive train exceeds the speed of the rear drive train.