a fluid power assist rack and pinion steering system for a vehicle having steerable wheels comprises a rack connected with steering linkage of the vehicle for , upon movement of the rack , moving the steering linkage to effect turning of the steerable wheels . a rotatable pinion is in meshing engagement with the rack . the steering system also includes a control valve comprising a valve core rotatable relative to a valve sleeve . a first part connects the valve sleeve for rotation with the pinion . a mechanism resists relative rotation between the valve core and the valve sleeve as vehicle speed increases by placing axial force on the valve sleeve . a second part on the valve sleeve resists axial movement of the valve sleeve relative to the valve core .