Buick LeSabre 1965 Service Manual page 477

STEERING GEAR, STEERING COLUMNS AND LINKAGE
POWER STEERING 8 - 1 3
When there is resistance to turn-
ing between the roadbed and the
wheels of the car, the parts at-
tach.ed to the worm will also re-
sist turning. Thus, when the
steering wheel is turned by the
driver, the torsion bar will de-
flect and allow the stub shaft and
valve spool to rotate with the
steering wheel. When this occurs,
the relationship between the valve
spool and valve body is changed
and oil flow is directed by the
slots on the valve spool through
the holes in the valve body to the
proper side of the rack-piston nut
to assist the driver. The torsion
bar deflection is limited to a pre-
determined amount. The upper
end of the worm has two tangs
which fit through slots in the valve
body cap and into two slots in the
end of the stub shaft. In case of
a power mechanism failure, the
stub shaft will contact the tangs
of the worm and steering will be
manual.
d. Oil Pump and Hoses
The oil pump, which is mounted
on the engine is driven by a belt
from the crankshaft pulley.
The pump reservoir encloses the
pump housing and provides a re-
serve supply of oil to assure
complete filling of the hydraulic
system. See Figure 8-18. The
reservoir cap is vented which
permits escape of any air that
may be introduced into the system
during assembly of the various
units and maintains atmospheric
pressure in the reservoir.
The pump housing encloses the
flow control valve and the rotor
assembly. The flow control valve
and spring are retained in pump
housing by the pressure union.
See Figure 8-19. This allows
servicing the flow control valve
without removing pump from the
engine. Inside the flow control
valve is the pressure relief valve.
Also in the end of the flow control
VALVE BODY TO
VALVE BODY CAP PIN
STUB SHAFT TO
VALVE SPOOL PIN
VALVE BODY PIN
TORSION BAR TO
STUB SHAFT PIN
Figure 8-17—Attaching Pins for Valve Parts
valve is a filter screen which
filters the oil that enters this
valve. The pressure union which
is the pump outlet, contains the
pump exit hole and an orifice.
The rotor assembly consists of a
drive shaft, a thrust plate, a rotor
with ten vanes, a pump ring and a
pressure plate. Oil enters the
rotor s e c t i o n of the housing
through a reservoir hole in hous-
ing which is open to the surround-
ing reservoir.
The rotor is loosely splined to the
end of the drive shaft, is located
adjacent to the face of the thrust
plate and is enclosed by the pump
ring. The rotor has a pressed-in
sleeve which f i t s through the
thrust plate and keeps the rotor in
alignment. The rotor vanes slide
radially outward to contact the
hardened and ground inside cam
surface of the ring. See Figure
8-20.
As the shaft and rotor rotate,
centrifugal force and fluid pres-
sure against the inner ends cause
the vanes to follow the cam con-
tour of the ring. The cam surface
is so shaped that two oppositt
pumping chambers are formed
which cause a complete pumping
cycle to occur every 180 degrees
of rotation of the rotor. The pump
ring has two crossover passages
drilled in it which transfers oil
from the thrust plate into a dis-
charge cavity located at the rear
of the pressure plate.
When the engine is started, each
pumping chamber picks up oil
from two openings, one between
the pressure plate and ring and the
other between the thrust plate and
ring. See Figure 8-18. The oil is
then propelled by the decreasing
pockets in each pumping chamber
into the discharge cavity through