Abstract: A hydraulic power transmission and braking system for vehicles in which individual hydraulic wheel motors are connected through suitable control apparatus to a variable displacement hydraulic pump which is driven by an appropriate power source. The displacement of the pump varies automatically in response to hydraulic fluid pressure and flow rate requirements imposed by the vehicle operating conditions. The power transmission control apparatus automatically switches from the 4-wheel drive mode to the 2-wheel drive mode as the vehicle accelerates past a predetermined speed. The braking control system proportions the braking force applied to each of the hydraulic wheel motors in accordance with the load imposed on that wheel by the vehicle operating conditions.