Abstract: A system for effecting the braking of a vehicle. The system is intended to be used with a vehicle which has an axle coaxial with a wheel engaging the surface over which the vehicle travels and which is rotatable with that wheel. The braking system includes a closed hydraulic circuit and a pump in the circuit which has an impeller rotatable by the axle as the vehicle moves over the surface. The invention includes structure for selectively, and sequentially, increasing the restriction of flow through the hydraulic circuit so that, as flow is restricted, a back-pressure is induced in the pump to apply a drag to the axle in a measure commensurate to the amount the flow is restricted.