An apparatus (10) for use in turning steerable vehicle wheels includes a rack gear (14) and a sector gear (16) which are disposed in meshing engagement. A lash adjustment assembly (46) is operable to move the sector gear (16) to reduce clearance between teeth (18 and 20) on the rack and sector gears upon rotation of the sector gear to an initial or on-center condition. The lash adjustment assembly (46) includes a force transmitting member (60) having a threaded end portion (90) which engages threads (92) on the sector gear (16). A power spring (100) is connected with the force transmitting member (60) and stores energy to rotate the force transmitting member relative to the sector gear (16). When the sector gear (16) moves to the on-center condition, an index pin (150) is moved relative to an index wheel (138) to release the force transmitting member (60) for rotation through a predetermined distance relative to the sector gear (16). When the force transmitting member (60) has rotated through the predetermined distance, an index pin (152) retains the index wheel (138) and force transmitting member against rotation.