POWER STEERING PUMP SERVICE
The service procedures for the Saginaw power steer-
ing pump are limited to the areas and components
listed below. No repair procedures are to be done
on the internal components of Saginaw power
steering pumps.
• Repair of power steering fluid leaks from areas of
the power steering pump sealed by O-rings is allowed
(See Pump Leak Diagnosis). However power steering
pump shaft seal leakage will require replacement of
the pump.
• Power steering fluid reservoirs, related components
and attaching hardware.
• Power steering fluid reservoir filler cap/dipstick as-
semblies.
Because of unique shaft bearings, flow control levels
or pump displacements, power steering pumps may be
used only on specific vehicle applications. Be sure that
the pump is only replaced with a pump that is the
correct replacement for that specific application.
Hydraulic pressure is provided for operation of the
power steering gear by the belt driven power steering
pumps (Fig. 1 & 2). It is a constant displacement, vane
type pump. The power steering pump is connected to
the steering gear by a power steering fluid pressure
hose and return line.
Rectangular pumping vanes carried by a shaft driven
rotor move the fluid from the intake to the cam ring
pressure cavities. As the rotor begins to turn, centrifu-
gal force throws the vanes against the inside surface of
the cam ring to pickup residual oil. This oil is then
forced into the high pressure area. As more oil is picked
up by the vanes. That additional oil is forced into the
cavities of the thrust plate through two crossover holes
in the cam ring and pressure plate. The crossover holes
empty into the high pressure area between the pres-
sure plate and the housing end cover.
When the high pressure area is filled. Oil flows under
the vanes in the rotor slots, forcing the vanes to follow
the inside oval surface of the cam ring. As the vanes
reach the restricted area of the cam ring, oil is forced
out from between the vanes. When excess oil flow is
generated during high-speed operation. A regulated
amount of oil returns to the pump intake side through
a flow control valve. The flow control valve reduces the
power required to drive the pump and holds down
temperature build-up.
When steering conditions exceed maximum pressure
requirements, such as turning the wheels against the
stops. The pressure built up in the steering gear also
exerts pressure on the spring end of the flow control
valve. This end of the valve houses the
PUMP LEAKAGE DIAGNOSIS
.
STEERING
19 - 9