Chevrolet 70 1969 Series, Shop Manual

Page: 479 / 913

STEERING SYSTEM 9B-28
After heating the oil to at least 150°F., set
engine idle to 450 rpm; then turn the steering
wheel from one end to the other and read pressure
on gauge while holding the wheel momentarily
against the stops. The reading should be the max­
imum with engine idling at 450 rpm. If it is not,
trouble is in the hydraulic circuit, but it does not
indicate whether the pump or steering gear or both
are at fault.
This can be determined by performing Test #2
and comparing it with Test #1.
Test #2 is Performed With the Oil Circuit
Closed. Set engine idle at 450 rpm and turn the
shut-off valve of gauge to the closed position.
N O T E : Shut-off valve must be located between
POWER STEERING
There are three power cylinders covered in
this section. The power cylinder acts as a power
assist to the mechanical steering. Refer to "Speci­
fications” at end of this section for power cylinder
application on each series vehicle.
On conventional cab models, a side mounted
cylinder is bracketed to the frame side rail at one
end and to the Pitman arm at the other end. On
conventional cab models equipped with the F-160
front axle, an additional right-hand power cylinder
is bracketed to the frame side rail at one end and
to a right-hand idler arm at the other end.
On tilt cab models, the power cylinder is
bracketed to the front axle at one end and to the
steering tie rod at the other end.
Stationary metal tubes and flexible hose as­
semblies carry hydraulic fluid to the cylinder to
operate the piston for right and left turns.
When the driver turns the steering wheel, the
control valve on the steering gear housing directs
hydraulic fluid, under pressure from the hydraulic
pump, to either side (depending on whether a right
or left turn is being made) of a piston in the power
cylinder (fig, 10). This produces movement of the
piston and attached steering linkage. The force ap­
plied by the power cylinder is the amount of thrust
necessary for all steering requirements.
On completion of a turn, reduced effort on the
steering wheel allows steering geometry of the
vehicle to return front wheels to a straight-ahead
the gauge and steering gear. Observe pump pres­
sure on gauge at idle and compare it with Test #1.
Diagnosis of the Two Tests. If the first test is
below specifications and the second test is equal
to specifications, or greater, the steering gear is
at fault. When the first test is below specifications
and the second test is not more than 50 psi greater,
the pump is at fault.
N O T E : If steering gear is found to be at fault,
use the troubleshooting procedures for the steer­
ing gear described under "Trouble Shooting The
Power Steering Gear" earlier in this manual.
N O T E : For additional troubleshooting inform­
ation, refer to "Quick Reference Troubleshooting
Chart” later in this section.
POWER CYLINDER
position. When returning to a neutral position, oil
on one side of the piston is forced back to the hy­
draulic pump reservoir by oil on the other side of
the piston, equalizing the oil pressure. This con­
stant amount of oil in the cylinder acts as a shock
absorber to dissipate road shock to the operator.
N O T E : The same procedure applies to vehicles
equipped with the F-160 front axle except that hy­
draulic fluid, under pressure from the hydraulic
pump, is directed through a junction block to either
side of a piston in the right and left power cylin­
ders. This causes one cylinder piston and attached
steering linkage to extend and the other to retract
(depending on whether a right or left turn is being
made).
The power cylinders used on these vehicles
are of the same basic design for all models. The
only difference is in the stroke length which for all
models is dependent upon the axle capacity. On
conventional cab models, the power cylinder piston
rod is threaded directly onto the piston.
POWER CYLINDER REPLACEMENT
R E M O V A L
1. Clean dirt from around hose connections at
the power cylinder.
2. Disconnect hoses from power cylinder,
catching hydraulic fluid in a suitable clean con­
tainer. Cover hose fittings and ports in cylinder.
Figure 10— Power Cylinder Oil Flow (Typical)
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L