In certain machines, such as construction equipment, it is desirable to provide a supplemental fluid supply for hydraulic steering systems to maintain sufficient fluid flow should a failure occur in the primary fluid supply. It is also desirable to provide retarding or dynamic braking to help control speed of the machine when operating downhill with a heavy load. A ground driven pump is provided to supply fluid to a selector valve for selectively directing the output of the ground driven pump to a steering system or a dynamic braking system. The selector valve is responsive to pressure in the steering system to direct flow from the ground driven pump to the steering system when the pressure drops below a predetermined level. The operator may selectively direct flow from the ground driven pump to the dynamic braking system when dynamic braking is needed. A dynamic braking valve may be operator controlled to regulate the degree of dynamic braking required to maintain the desired machine speed under specific operating conditions. In this manner a supplemental supply is provided which may be selectively directed to the steering system or the dynamic braking system.