A hydraulic control system for a hydrostatic transmission in which are provided valving means which can be selectively positioned corresponding to forward, neutral or reverse drive of the transmission and including means for dumping excess fluid pressure from the fluid pressure circuit in order to prevent damage to the transmission and under certain conditions to prevent overspeeding of the transmission to further prevent damage. Means are provided whereby fluid flow in the hydrostatic loop can be bypassed from its normal drive path in the transmission, through the valve means provided.