GMC 4000 Series Service Manual page 513

Sec.9B
Page 502
POWER STEERING
CONTROL VALVE AND POWER STEERING GEAR (Cont.)
C O ND ITIO N
8. Truck leads to one
Due to front end m isalignm ent.
side or to the other.
Unbalanced or badly worn valve.
NOTE:
very light in direction of lead and heavy in oppo­
site direction.
9. Momentary in­ Low oil level in pump.
crease in effort
Pump belt slipping.
when turning
wheel fast.
10. Excessive wheel Lash in steering linkage.
kick-back or loose
A ir in the system .
steering.
Excessive lash between pitman shaft sector and
ball nut.
Loose thrust bearing adjustm ent.
11. Steering wheel Loose pump belt.
surges or jerks
when turning with
engine running—
especially during
parking.
12. Hard steering Loose pump belt.
when parking.
Low oil level in reservoir.
Lack of lubrication in linkage for front suspension.
T ire s not properly inflated.
Insufficient oil pressure.
G M C S E R V I C E M A N U A L
CAUSE
If this is the cause, steering effort w ill be
REMEDY
A djust to specification.
Replace valve.
Check oil level in pump reservoir and bring to proper level.
Tighten or replace belt.
A d just parts affected.
Add oil to pump reservoir.
Adjust to specification.
Remove steering gear and adjust to specification.
Adjust to specification.
Adjust to specification.
Fill to proper level. If excessively low, check all lines and joints
for evidence of external leakage.
Add lubricant where needed as described in lubrication (S e c. 0 )
of this manual.
Inflate to recommended pressure.
If all of the above checks do not reveal the cause of hard steering,
make the following tests of oil p ressu re:
a. Disconnect the pressure line at oil pump. Attach gauge to pump.
Connect the hose to end of gauge where the valve is located.
b. With the engine at warm idle and gauge valve open, note the
oil pressure on the gauge while turning steering wheel from one
extrem e position to the other. Especially note the m axim um
pressure which can be built up with the wheel held in either
right or left extreme position. CAUTION:
extrem e position for an extended period of tim e because it will
drastically increase the oil tem perature and will cause undue
wear on the oil pump.
c. With oil tem perature between 150 degrees F and 170 degrees
F, as measured with a therm om eter in the reservoir, the m a xi­
mum oil pressure should not be less than 600 PSI for s a tis ­
factory power steering operation.
d. If the maximum oil pressure is less than 600 P S I, it indicates
trouble in the pump, steering gear, cylinder, or a combination
of these parts. To elim inate the gear, close the gauge valve
and quickly test pressure of the pump only with the engine at
warm id le ; then open the valve to avoid
tem perature.
Do not hold wheel in
increasing oil