Abstract: An apparatus for automatically controlling the number of drive wheels to which power is applied in accordance with the range in which the transfer case is operated. In the low range of operation, including reverse, the drive power is supplied solely to the rear wheels. In the higher range, the number of drive wheels to which drive power is applied is in accordance with the operator settings. A pair of, for example, locking hubs that are actuated by vacuum, air or hydraulic power appropriately routed to the wheels and controlled by an electrically driven valve is operated, in conjunction with the transmission or transfer case shifting mechanism. The arrangement provides a means for automatically reducing the stress on the transmission and transfer case when the vehicle is operated in the four wheel drive mode.