Power Steering Gear and Pump

The hydraulic power steering system consists of a pump, fluid reservoir, steering gear, pressure hose and return hose. The power steering hoses connect the gear to the pump. The engine drives the pump by a drive belt. In some cases, a cooler is also present to provide cooling for heavy duty or trailering applications.

POWER STEERING GEAR
The power steering gear has a re-circulating ball system that acts as a rolling thread between the worm shaft and the rack piston. The worm shaft is supported by a preloaded thrust bearing and two conical thrust races at the lower end, and a bearing assembly in the adjuster plug at the upper end. While the worm shaft is being turned to the right position, the rack piston moves up in the gear. Turning the worm shaft left moves the rack piston down in the gear. The rack piston teeth mesh with the sector, which is part of the pitman shaft. Turning the worm shaft turns the pitman shaft, which turns the wheels through the steering linkage. The control valve in the steering gear directs the power steering fluid to either side of the rack piston. The rack piston converts the hydraulic pressure into a mechanical force. If the steering system becomes damaged and loses hydraulic pressure, the vehicle will still have its manual control. For unit repair for the steering gear, refer to Power Steering Gear Unit Repair.

POWER STEERING PUMP
The hydraulic pump is a vane-type design using a fluid reservoir that is separate from the pump housing. There are two bore openings at the rear of the pump housing. The larger opening contains the cam ring, pressure plate, thrust plate, rotor and vane assembly, and end plate. The Electronic Variable Orifice (EVO) system increases or decreases the amount of fluid leaving the power steering pump. This provides the driver with a comfortable balance of steering wheel feel and full power assist.
At vehicle stand still or very low speeds, the system allows full hydraulic fluid flow for maximum power assist and reduced steering effort. As the vehicle gains speed, a variable orifice closes at the steering pump which reduces the pump fluid flow. This action provides a stiffer steering wheel response for improved road feel and greater directional stability at highway speeds. For unit repair of the steering pump, refer to Power Steering Pump Unit Repair.