Abstract: A method and apparatus are disclosed for mechanically steering vehicles such as crawler tractors and the like or skid steer tractors, which include a pair of independently operable power sources. The apparatus includes a pair of independent first linkage systems interconnected between a single operator control lever and each respective power source to achieve equivalent power outputs from the sources upon movement of the lever. A pair of independent second linkage systems are interconnected between respective links in the first linkage system and respective throttling means. In the method, each throttling means may be operated independently of the other to achieve unequal power outputs from the two sources by virtue of the independent first and second linkage systems.