Abstract: To override the vehicle immobilizing effect of a failed automatic ratio controller in a hydromechanical transmission, the conventional manually shiftable range selector is loosely linked with a ratio arm while the latter is being stroked by the controller to vary hydrostatic output speed. Upon controller failure, the range selector is drivingly linked with the ratio arm, such that shifting movements of the range selector are translated into stroking movements of the ratio arm to provide manual control of vehicle propulsion. Safeguards are provided to ensure that conversion between the normal propulsion mode governed by the automatic ratio controller and the override propulsion mode manually governed by the vehicle operator is effected in a safe manner.