A countershaft type power transmission (10) has a plurality of hydraulically actuated synchronisers (20,26,46,48) which are selectively operable to establish the gear ratios in the transmission. Each synchroniser is effective to control one or more ratios and is positionable between neutral positions. A hydraulic control system is provided to control the movement of the synchronisers and to hydraulically force each synchroniser to neutral when it is not called upon for ratio establishment. <IMAGE>
