Certain design and performance benefits are realized by utilizing hydrostatic transmission (HST) for vehicle propel drives. The component nature of the HST provides design flexibility to build the transmission into the machine and not require the carriage be built around the transmission. This feature may result in lower design and installation costs and potentially better control over vehicle dynamics. Other benefits derived from HST characteristics: A. Load carrying capability is independent of engine speed. B. Maximum drawbar pull is available over a wide engine speed range. C. Hydrostatic braking. D. Vehicle inching. E. Potential for fuel savings. The typical HST control is the displacement type. The pump or motor displacement is regulated by a mechanical, hydraulic or electrically signaled servo valving. The servo valve characteristically eliminates displacement error. Displacement controls require skilled and wary operators or excessive engine power to prevent inadvertent engine stalling under all vehicle loading and speed possibilities.