Abstract: For a part time four wheel drive vehicle, auxiliary drive power is handled by an interaxle transfer mechanism comprising a braked differential gear set interposed in the vehicle's auxiliary motive power path, providing, in addition to the normal two wheel drive mode and front-rear-locked four wheel drive mode, a limited-slip-auxiliary four wheel drive mode. The differential gear set may be of the planetary or bevel gear type; its reaction gear is coupled to a braking unit, preferably of the hydraulic disk-pad-caliper type which is readily accessible and highly serviceable. The transfer mechanism is typically interposed concentrically at the driven end of the vehicle's auxiliary driveshaft, and may be retrofitted onto existing vehicles of the type having a gear or chain driven offset auxiliary driveshaft by adding an extension gear casing which carries the braking unit externally.