Abstract: It has been proposed to employ a constant mesh gearbox of the kind having pairs of gears on parallel shafts in constant mesh with each other, together with a clutch, in an automatic vehicle transmission. A microprocessor controls actuators for the clutch and throttle and hydraulic actuators for moving the selector rod of the gearbox, in order to give automatic operation of the gearbox.In accordance with the invention, a constant mesh gearbox of the kind referred is provided with actuating means for moving the selector shaft and, in at least one direction of travel of the selector rod, the actuating means acts via resilient means which is arranged to store the energy of the actuating means when the actuating means is operated but the selector rod is not free to move, the rod being moved by the energized resilient means when the selector rod becomes free.