This paper concerns mechanical fully automatic power transmissions for buses and trucks. Their design concept offers an additional two-pedal-controlled mechanism in conjunction with any conventional gearbox. The prototype consists of a five-speed gearbox and a single-plate clutch actuated by a transistorized electropneumatic control system. The electronic unit computes the shift points according to the accelerator pedal position, the vehicle speed and the selection of shift modulation, and controls the electric and pneumatic units for both clutch engagement and gear shift. The principal functions of the prototype are: (1) the selection switch of shift modulation offers either a high-power acceleration shift mode or an economical-power cruising mode, (2) thyristors ensure the correct sequence control of clutch and gear operations, (3) the clutch servomechanism engages the clutch in a three-stage (quick, slow, quick) action and disengages quickly and (4) for a non-synchromesh gearbox, the double-clutch-action control mechanism and the throttle servomechanism actualize the synchronization of gears.The proposed transistorized electropneumatic control system was installed in a sixty-passenger bus and tested under various conditions. The results show that the prototype has practical applicability in view of its performance and feasibility of production.