A valve positioner for controlling a valve closure element is provided. The positioner includes a positioner housing with a plurality of fluid flow passageways in fluid communication with a fluid supply source and the valve closure element. The positioner housing is configured to receive a detachable spool manifold assembly. The spool manifold assembly is positioned adjacent the plurality of fluid flow passageways. The spool manifold assembly includes a reciprocally moveable spool configured to selectively port fluid flow from the plurality of fluid flow passageways. The spool manifold assembly includes a diaphragm connected to the spool via a flexible shaft. The diaphragm is in fluid communication with a transducer for receiving a fluid causing the diaphragm to expand or contract and thereby displacing the spool. The flexible shaft is radially elastic in order to minimize axial backlash between the diaphragm and the spool. The flexible shaft configuration minimizes the spool stroke.