GMC 4000 Series Service Manual page 498

Section
D e s c r ip t io n ............................................................................................. ..........487
Maintenance
Power Steering Gear and Control V a l v e ..................................................489
Troubleshooting The Power Steering G e a r ...........................................491
Power Steering Hydraulic P u m p ................................................................492
Troubleshooting The Hydraulic Pump
Power Steering, Power C y lin d e r ................................................................497
Troubleshooting the Power Cylinder
Oil Cooler
Quick Reference Troubleshooting C h a r t ....................................... ..........500
S p e c ific a tio n s ....................................................................................................504
DESCRIPTION
The power steering system provides automatic
hydraulic assistance to the turning effort applied
to the mechanical steering system .
The power steering system consists of a con­
trol valve, power cylinder, and a hydraulic pump
used in conjunction with the steering gear. An oil
cooler is attached to front of radiator on all ve­
hicles except those equipped with air conditioning.
The power steering system is a complete in­
line unit. The steering shaft, hydraulic valve, worm,
and ball nut are in a line, making a compact, space-
saving steering gear. The recirculating ball-type
mechanical steering gear is used in conjunction
with the control valve.
The power steering will not operate without
driver guidance; therefore, when turning effort is
relieved, the front wheels return to neutral or
straight ahead position.
The power cylinder is actuated by operation
of the control valve which supplies hydraulic fluid
to either side of the power cylinder piston as re­
quired, depending on the position of the valve. The
pressure used to operate this system is supplied
by either a vane-type or slipper type oil pump.
If, for any reason, the power steering system
should fail, the control valve "locks up" and the
steering gear operates manually, giving the driver
full control of the vehicle. Although greater manual
effort will be required to operate steering mech­
anism.
On all hydraulic pump models, the fluid re ser­
voir either encases the pump or is mounted on top
of the pump. An additional reservoir is mounted on
a bracket attached to the radiator support on con­
G M C S E R V I C E M A N U A L
SECTION 9B
Po-w&i Stee/Una
Contents of this section are listed in Index below:
*
....................................................................................................487
............................................................................................. ..........499
POWER STEERING SYSTEM
Page No.
........................................... ..........495
........................................... ..........499
ventional cab models or to the transmission con­
trol island panel front support on tilt cab models.
MAINTENANCE
The power steering system requires little
maintenance. However, the hydraulic system should
be kept clean to ensure maximum operating p er­
formance and trouble-free service. Periodic in­
spection to check for leaks should also be made.
At regular intervals the pump hydraulic fluid
level in the reservoir should be checked and fluid
added when required. Refer to LUBRICATION (SEC.
0) for type of fluid to be used, method, and inter­
vals for filling.
When the slightest evidence of dirt, sludge,
or water is discovered in the system , drain and
refill with clean hydraulic fluid recommended in
LUBRICATION (SEC. 0) of this manual. To drain
system , disconnect fluid lines at power cylinder.
Air in the fluid system will cause spongy action
and noisy operation. When any hose has been dis­
connected or when fluid has been lost for any rea­
son, the system must be bled after adding fluid.
Bleed system as directed later in this section under
"Bleeding Hydraulic System."
Should the power steering system become in­
operative due to loss of hydraulic fluid, pump p res­
sure line should be re-routed from pump outlet
directly back to pump reservoir.
IMPORTANT: DO NOT operate pump without
fluid in pump reservoir.
The hydraulic pump, control valve, and power
cylinder do not require adjustment on the vehicle.
The only adjustments are on the steering linkage.
Adjustment of these parts are normally required
Sec. 9B
Page 487