Chevrolet 70 1969 Series, Shop Manual

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STEERING SYSTEM 9B-23
1. Hard steering while driving. 5. Excessive wheel kickback.
2. Poor return of steering. 6. Steering wheel jerks.
3. Leads to one side or the other. 7. Hard steering when parking
4. Momentary increased effort on fast turn. 8. Effortless turn.
POWER STEERING HYDRAULIC PUMP
Six positive displacement vane type hydraulic
pumps and two positive displacement slipper type
hydraulic pumps are used on vehicles covered by
this manual. Refer to “ Hydraulic Pump Model
Application" in “ Specifications” at end of this
section for proper pump application on each truck
series.
VANE TYPE HYDRAULIC PUMP
The vane type hydraulic pumps, except model
235-P-47, used in conjunction with the F-160 front
axle, have a maximum output of 3.5 gallons per
minute of Type " A " Automatic Transmission Oil
at 170 F., with pump operating at 1500 rpm against
50 psi pressure. Minimum output of the pump is
2.35 gallons per minute with pump idling at a speed
of 590 rpm, against 665 to 735 psi pressure.
Pump model 235-P-47 has a maximum output
of 4.8 to 5.2 gallons per minute of Type " A " Auto­
matic Transmission oil at 170°F., with pump oper­
ating at 1500 rpm against 50 psi pressure. Min­
imum output of the pump is 2.35gallonsper minute
with pump idling at a speed of 590 rpm against 665
to 735 psi pressure.
The hydraulic pump is mounted at front of en­
gine and is belt driven from the engine crankshaft
in conjunction with other accessories (fig. 6).
The oil reservoir encases the pump and on
some vehicles, an additional reservoir is remotely
mounted on the radiator front support or on the
transmission control island support.
On pump model 235-P-19, the drive shaft is
supported by a bushing in the pump housing. On all
other vane type hydraulic pumps, the drive shaft
is supported by one ball bearing and one needle
bearing in the pump housing.
The pump rotary group is the heart of the
pump and consists of the drive shaft, rotor, vanes,
pump ring, thrust plate, and pressure plate. The
flow control valve is the nerve center of the pump
and includes the flow control plunger, flow control
spring, and the pressure relief ball and spring.
This assembly controls flow and pressure in the
system.
PUMP O P E R A T IO N
N O T E : Refer to figures 7 and 8.
As the drive shaft rotates the rotor, the vanes
follow the cam surface in the pump ring. This cam
consists of two rising and falling areas which cause
a complete pumping cycle to occur every 180 de­
grees of rotation (fig. 7).
The spaces between rotor vanes pick up oil on
the rising portions of the cam from two openings
between thrust plate and pump ring and from open­
ings between the pressure plate and pump ring.
This oil is discharged on the falling portion of the
cam through two openings in the pressure plate
Pump Rofor
Dowel Pin
Hole
Pump Ring
>le A ' % \ H<
\
a
/
Crossover
Hole
Crossover
Hole
Figure 6— Power Steering Hydraulic Pump Installed (Typical)
Figure 7— Cross Section of Rotor and Vanes in Pump Body
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L