Chevrolet 10 Series 1968, Service Manual, Page: 545 / 713

STEERING 9-12
POWER STEERING
INDEX
Page
General D e s c r ip t io n ............................................................. ... 9-12
Maintenance and A d ju s tm e n ts ............................................. ... 9-12
Pow er Steering Gear A d ju s tm e n t................................... ... 9-12
Bleeding Hydraulic S ystem ................................................ ... 9-12
Fluid L e v e l .......................................................................... 9-13
Pump Belt T e n s io n ............................................................. 9-13
Hydraulic System C h e c k s ................................................ 9-13
Page
Component Replacement and R e p a i r s ................................ ...9-14
Pow er Steering P u m p ..........................................................9-14
Control Valve - C -10-C P-20-30 ................................... ...9-14
Pow er Steering Gear and Control V alve -
40-50-60 S e r ie s ................................................................ ...9-15
Pow er C y lin d e r ....................................................................9-15
Pow er Steering H o s e s .......................................................9-15
GENERAL DESCRIPTION
All truck power steering installations consist of three
basic components, pump, control valve and power cyl­
inder, connected by hydraulic lines. The pump is a vane
type with the mounting to the engine peculiar to the par­
ticular model and engine application involved.
Two types of control valves are used, light-duty models
use the linkage type mounted between the pitman arm and
relay rod. Medium and heavy-duty models use a rotary
valve type, mounted on the steering gear box between
the steering shaft and worm shaft.
The power cylinders used differ in capacity and mount­
ing. C10-20-30 series have the cylinder mounted between
the frame and relay rod. The mounting for units equipped
with 9000 lb. and 11000 lb. front axle is mounted on out­
side of side member (fig. 28). Axle-to-tie rod mounting
is used on all other models.
A ll 40-50-60 series models use a power steering oil
cooler mounted at the front of the vehicle.
MAINTENANCE AND ADJUSTMENTS
POWER STEERING GEAR ADJUSTMENT
C-10, CP-20-30
The steering gear used with power steering is adjusted
in the same manner as the manual steering gear.
40, 50 and 60 Series (Fig. 23)
Sector lash adjustment is the only power steering gear
adjustment that can be made on the vehicle. However, in
order to make this adjustment, it is also necessary to
check the combined valve drag and worm bearing preload.
1. Remove steering connecting rod from pitman arm.
2. Loosen sector lash adjusting screw locknut and back
off adjusting screw to the limit of its travel.
3. Disconnect horn wire and remove horn button cap.
4. Turn the steering wheel through its full travel, then
locate wheel at center of its travel.
5. Check combined valve drag and worm bearing pre­
load, with an inch-pound torque wrench on the steer­
ing shaft nut, by rotating through the center of travel
(approximately 10° in each direction). Note the
highest reading.
6
. Tighten the sector lash adjusting screw until torque
at steering wheel nut falls within specifications.
NOTE:
If maximum specification is exceeded,
turn lash adjuster screw counter-clockwise, then
come up on adjustment by turning adjuster in a
clockwise direction.
7. Tighten locknut and recheck pull as it must lie within
specifications.
8 . Reassemble steering connecting rod to pitman arm.
BLEEDING HYDRAULIC SYSTEM
1. Fill oil reservoir to proper level and let oil remain
undisturbed for at least two minutes.
2. Start engine and run only for about two seconds.
3. Add oil if necessary.
4. Repeat above procedure until oil level remains con­
stant after running engine.
5. Raise front end of vehicle so that wheels are off the
ground.
6
. Increase engine speed to approximately 1500 rpm.
7. Turn the wheels (off ground) right and left, lightly
contacting the wheel stops.
8
. Add oil if necessary.
9. Lower the vehicle and turn wheels right and left on
the ground.
Fig. 2 3 - 4 0 - 5 0 - 6 0 Series Power Steering G ear and
Control V a lv e (T yp ica l)
CHEVROLET TRUCK SERVICE MANUAL