Steering Gear: Description and Operation

NOTE: The steering gear is serviced as an assembly. If any service is required, the entire power steering short rack must be replaced.

DESCRIPTION
The steering gear housing and valve housing are combined into a one-piece aluminum die casting.
^ The gear design incorporates quick connect fittings for the power steering left turn pressure hose and power steering return hose that allow the lines to swivel (when detached from heat shield bracket). This is normal and does not indicate loose fittings.
^ If the fittings leak, check to make sure they are tightened to specification. To prevent port seat damage, do not overtighten.
^ If tightening the fittings to specification does not eliminate the leak, replace the fitting seals.
^ The steering gear is a hydraulic-mechanical unit which uses an integral piston and rack design to provide power-assisted vehicle steering control.
^ Internal valving directs pump flow and controls pressure to reduce steering effort during operation.
^ Steering gears available for service are power steering short racks and contain:
- A rotary hydraulic fluid control valve integrated to the power steering gear input shaft and control.
- A boost cylinder integrated with the steering gear rack.

HYDRAULIC OPERATION
The power rack and pinion steering gear uses an integral valving that directs pump flow and controls pressure as required to reduce steering effort during operation. The power rack and pinion steering gear contains:
^ a rotary valve for hydraulic fluid control which is integrated to the power steering gear input shaft and control.
^ a boost cylinder integrated with the steering gear sector shaft.
Rotary Valve
The rotary design control valve directs fluid flow using relative rotational motion between the input shaft and valve sleeve. The amount of steering assist is relative to the amount of effort applied at the steering wheel. At a given vehicle speed, steering assist increases with driver effort.
^ When the steering wheel is turned, resistance of the wheels and the weight of the vehicle cause a torsion bar to deflect.
^ This deflection changes the position of the input shaft metering edges and the sleeve slot edges, directing pressurized fluid to the appropriate end of the power cylinder.
^ The difference in pressure forces on the piston helps move the steering gear sector shaft to assist turning effort. The piston is attached directly to the steering gear sector shaft and the steering gear housing functions as the power cylinder.
^ The fluid in the opposite end of the power cylinder is forced to the control valve and back to the power steering pump reservoir.
^ When the driver stops applying steering effort, the valve is returned back to a centered position by the torsion bar.
^ When this occurs, pressure is equalized on both sides of the piston and the front wheels tend to return to a straight-ahead position.