An apparatus (10) for turning steerable wheels of a vehicle comprises a housing (14) that defines a fluid chamber (24). A rack bar (26) extends longitudinally through the housing (14) and is connectable with the steerable wheels of the vehicle. The rack bar (26) is movable relative to the housing (14) for turning the steerable wheels. A piston assembly (34) is fixedly attached to the rack bar (26) and sealingly engages the housing (14). The piston assembly (34) divides the fluid chamber (24) into first and second chamber portions (40 and 42). A fluid source (80) directs fluid toward one of the first and second chamber portions (40 or 42) for creating a differential pressure between the first and second chamber portions (40 and 42). The piston assembly (34) and the rack bar (26) move relative to the housing (14) in response to the differential pressure. The piston assembly (34) includes structure (132) for dampening fluid pulsations emanating from the fluid source (80).