Abstract: The power train between the engine and drive wheels of a motor grader, for example, comprises a normally engaged main engine clutch, a high-low power shift range transmission, and a four speed reversible power shift main transmission. The main engine clutch is releasable manually by a clutch pedal or releasable automatically by a hydraulically operated clutch release cylinder. The range transmission is shiftable into high or low by supplying hydraulic fluid to power shift clutches therein. The main transmission is shiftable into forward, reverse or neutral by manual operation of a direction selector valve. The main transmission is also shiftable into each of its speed ranges by axially moving the spool of a speed selector valve. The spool of the speed selector valve is axially movable into four positions by a hydromechanical linkage comprising three hydraulic shift cylinders.