In a manually operable shift assembly a plurality of fork shafts are arranged within a gear case and each fork shaft is axially displaceable between two different gear positions by a gearshift lever which engages a recess within the fork shaft. One of the fork shafts is axially movable between a forward gear position and a reverse gear position and the fork shaft alongside it is movable between two forward gear positions. To prevent accidental engagement in the reverse gear position when shifting into or out of its associated forward gear position a limiting or restricting action is provided which must be overcome before movement into the reverse gear position can be attained. In one embodiment, the restricting action is provided between a plate mounted on the gearshift lever and a spring biased member arranged within the gear case. In another embodiment the limiting action is provided by spring biased pins located in the recess in the fork shaft. Additionally, the shifting movement can be effected by means of an intermediate rod and lever assembly disposed between the gearshift lever and the fork shaft with the restricting action afforded between the lever on the intermediate rod and a spring biased pin positioned in the gear case at a location spaced from the fork shaft.