Abstract: A unique double acting piston and cylinder assembly is disclosed wherein the assembly can be moved to any one of three positively determined positions by application of fluid pressure to any one of three ports.

Abstract: A gear changing system is disclosed for changing the gears in one or more automotive or truck transmissions of the mechanical type. Each rail or equivalent linkage for supporting and moving the gear changing fork is connected to the operating shaft of a fluid actuated cylinder assembly which has fluid ports connected to a plurality of control valves. The valves are connected, on one side, to a source of fluid under pressure, preferably pneumatic, and on the other side are vented to a reservoir or the atmosphere. An electrical or electropneumatic control system controls the operation of the valves, the control system including a push button selector which chooses a shift gear ratio to be attained. The push button assembly first operates a "neutral" valve which causes the cylinder means to move each shift rail to neutral.