44 is overcome by the supplementally applied torque such that four way control valve 30 becomes operational in a known manner for generating a 34 hydraulically derived 34 steering force for augmenting the 34 mechanically derived 34 steering force the supplemental torque causes valve spool 34 to move rotationally with respect to valve sleeve 32 valve sleeve 32 is positioned within valve chamber 28 and is located axially and tangentially with respect to pinion shaft 14 by connecting pin 36 via hole 46 formed in axially extending tab 48 of valve sleeve 32 valve spool 34 is located radially and in pitch and yaw by bearings 50 and 52 and axially by torsion bar 42 and drive pin 54 valve sleeve 32 is located radially and in pitch and yaw by its interfacing fit upon valve spool 34 the hydraulic elements of four way rotary control valve 30 are configured in the exemplary embodiment shown in an 34 open center 34 valving arrangement however it will be understood that preload mechanism 44 and its various alternative constructions to be disclosed hereinafter are also readily adapted for use in closed centered valving arrangements the pressurized source of hydraulic fluid supplied by the pump not shown enters four.