Abstract: A control system for a synchromesh unit, particularly suitable for controlling a synchromesh in a forward/reverse pre-select gear change system. The system is purely hydraulic, incorporating a double acting hydraulic cylinder (1) for moving the synchromesh. The hydraulic circuit controlling the hydraulic cylinder (1) includes restrictions (R.sub.1), (R.sub.2A), (R.sub.2B) and an accumulator (10), which vary the force applied by the hydraulic cylinder (1). The variation of the force applied by the hydraulic cylinder (1) includes a gradual, progressive increase of force whilst the synchromesh is matching its speed to the gear to be engaged, and subsequently allowing the synchromesh mechanism to move rapidly once its speed is matched with the gear to be engaged, to quickly move the teeth of the synchromesh and the gear to be engaged together. The force applied by the hydraulic cylinder is then increased again to a maximum once the synchromesh is fully engaged.