GMC 4000 Series Service Manual page 499

Sec. 9B
Page 488
POWER STEERING
H y d r a u lic \
R etu rn
(
P u m p
H o se
Figure 1 — Checking Pum p Hydraulic Pressure
(Vane Type Pum p ) (Typical)
only when the units have been removed or dis­
connected.
NOTE: These adjustments, with the exception
of the power cylinder piston rod end, are the same
as previously described in "MECHANICAL STEER­
ING" of this group.
Wheel alignment must be maintained to proper
specifications. Refer to FRONT SUSPENSION (SEC.
3) of this manual, for proper procedures for check­
ing front end alignment. Improper tire inflation
will also affect operation of the power steering. The
tires should be checked at regular intervals.
Because of the power assist from the power
steering system it is more difficult to detect de­
fects in the steering system . Therefore, periodic
maintenance is very important on a vehicle having
power steering.
BLEEDING HYDRAULIC SYSTEM
When a power steering pump or power cylin­
der has been installed or a disconnected oil line
has been reconnected, the air that has entered the
system must be bled out before the vehicle is again
operated. If air is allowed to remain in the hy­
draulic fluid system , noisy and unsatisfactory
operation of the steering system will result. Bleed
air from the hydraulic system as follows:
NOTE: When hydraulic fluid is added to power
steering system , fluid should be poured through a
200 mesh wire screen. Use only the hydraulic fluid
recommended in LUBRICATION (SEC. 0) of this
manual.
1. Fill pump fluid reservoir to proper level
and let fluid remain undisturbed for about two
minutes.
2. Raise front end of the vehicle so that front
wheels are off the ground.
G M C S E R V I C E M A N U A L
P re ssu re
"stops" to eliminate air pockets in the power cyl­
C h e c k in g
inder. Continue this operation until fluid in reser­
G a u g e
voir stops bubbling. Maintain fluid level during
this operation.
P re ssu re
H o se
utes, turn wheels to right and left as before.
DO NOT HIT THE WHEEL STOPS. Recheck fluid
level and hose connections for leaks. Continue this
operation until fluid in reservoir is clear.
1500 rpm and continue running at this speed until
all signs of air bubbles cease to appear in reser­
G a u g e
voir. Turn wheels (off the ground) to right and left.
V a lv e
DO NOT HIT THE WHEEL STOPS.
ground. Recheck for leaks.
required.
VANE-TYPE HYDRAULIC PUMPS
the hydraulic pump. Connect a 0 to 2000 psi p res­
sure gauge (J-22181) between the pressure hose
and the pump pressure port. Leave valve in p res­
sure gauge line open (fig. 1).
all air from pressure line as directed previously
under "Bleeding Hydraulic System."
wheels through normal operating range several
tim es until the hydraulic fluid temperature reaches
170°F. When fluid temperature reaches 170°F.,
close valve in pressure gauge line and observe
reading on pressure gauge. Pressure reading
should be within 900-1000 psi.
wheels to extreme right and left against "stops"
(with wheels on ground). At extreme right or left
position the maximum pressure reading should be
within the amount specified in procedure 3 above.
SLIPPER TYPE HYDRAULIC PUMP
pressure line at pump. Connect a 0 to 2000 psi
pressure gauge (J-22181) to the pump outlet; then
connect a shut-off valve between the pressure
gauge and pressure line (fig. 2). Make sure all
connections are tight and that shut-off valve is
fully open.
between the pump and the shut-off valve.
at idle speed. Turn wheels from right to left sev ­
eral tim es to expel all air from system and to
bring fluid temperature to approximately 170°F.
3. Turn wheels to right and left to wheel
4. Start the engine and run at idle for two min­
5. Increase engine speed to approximately
6. Lower the vehicle and turn wheels on the
7. Check fluid level in reservoir and refill as
HYDRAULIC PRESSURE TEST
1. Disconnect pressure hose from fitting at
2. Bleed steering hydraulic system to remove
3. Start engine and run at idle speed. Turn
4. Open valve in pressure gauge line. Turn
1. Disconnect hydraulic pump to steering gear
NOTE: The pressure gauge must be installed
2. Start the engine and run for several minutes