A front wheel drive speed control system for a vehicle having a main rear wheel drive and an assisting hydraulically powered front wheel drive. A hydraulic pump is connected by a hydraulic circuit to a hydraulic motor at each driven front wheel. A clutch assembly between the hydraulic motor and the associated wheel facilitates rotation of the driven front wheel. A speed sensing device is mounted to sense speed of the main rear wheel drive and each driven front wheel. A speed control system is connected to the speed sensing devices and to the hydraulic pump and is operable to terminate the pumps operation when the speed of the main rear wheel drive exceeds a predetermined speed and to resume assisting operation of the driven front wheel when the speed of the main rear wheel drive drops below a second predetermined speed.