The Sheppard M-Series Integral Power Steering Gear provides full-time hydraulic steering. Only enough manual
effort to overcome the torsion bar and turn the rotary valve is required.
The actuating shaft (1) is connected to the steering column and is centered within the rotary valve by a torsion
bar. The rotary valve shaft is threaded into the piston with ball threads (2) and travels within the piston on steel
balls. Circular motion on the actuating shaft causes high pressure fluid to build up on one end of the piston.
This higher pressure causes the piston to move in the bore of the gear housing. The sector shaft (3) is engaged
to a rack gear (4) machined into one side of the piston. Piston rack movement causes sector shaft and pitman
arm rotation. When steering shaft rotation stops, the actuation valve returns to its neutral position. Relief valve
plungers or adjustable stops are used in the bearing cap and cylinder head. When the plungers are adjusted prop-
erly, they will unload the hydraulic system if the wheels are in a full turn to either direction.
When the engine is running there is constant low pressure oil flow through the steering gear. This constant oil
flow provides an instant response and absorbs road shock to help eliminate steering wheel kick. Pressure is equal
throughout the steering gear; however, care should be used on towing or moving a vehicle where the engine or
hydraulic supply pump is not running.
If sudden loss of pressure occurs during normal driving, the parts are designed to pro-
vide mechanical back-up steering so that the vehicle may be safely steered to the side of
An optional integral pressure relief valve is available on the M-Series Steering Gears. This valve limits maximum
steering system relief pressure at the steering gear. This reduces system temperature by avoiding high pressure
by-pass and recirculation within the pump.
The Sheppard Integral Power Steering Gears have been designed to provide long service life and simple service
repair. The rack and sector shaft does not require center point adjustment. The clearance between the cylinder
bore and the piston is closely controlled, and piston ring (5) was added to better use the hydraulic oil supplied.
With reasonable care and limited maintenance the Sheppard M-Series Steering Gear will provide many miles
of reliable performance.