Abstract: 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.

Abstract: A steering system for a construction vehicle operable to control the position of a pair of front wheels and a pair of rear wheels relative to the frame of the vehicle includes a hydraulic fluid circuit for distributing hydraulic fluid. A hydraulic cylinder is connected to each of the wheels for turning same in a desired manner. A steering wheel is interposed in the hydraulic fluid circuit for selectively directing hydraulic fluid to the cylinders for steering said wheels in a desired direction. A mode selector valve is interposed in the fluid flow circuit between the steering wheel and the cylinders for selectively selecting either four-wheel steer, crab steer, or front-wheel steer mode of steering for said vehicle. A control momentarily overrides the mode selector valve to isolate the rear hydraulic cylinders from the front hydraulic cylinders for permitting independent movement of the rear wheels of the vehicle.