Abstract: An automatic gearbox has a planetary gear system and fluid pressure operated friction elements which are operable to act on the gear system to change the gear ratios thereof. Operation of the friction elements is controlled by electronic circuits on the basis of electrical signals indicative of vehicle speed and throttle opening. A manually operable switch is provided for selecting reverse gear and for providing manual overriding signals for the selection of forward gears. The electronic circuits are so arranged that, when a gear is selected manually, operation of the friction elements associated with the gear or gears higher than the selected gear is not carried out until vehicle speeds at least equal to the vehicle speeds at which the said friction elements are operated at full throttle opening in the automatic mode of operation.