Chevrolet 1977 light duty truck Service Manual page 221

CONDITION
Low oil pressure due to steering
pump:
(See pump pressure test.)
Note: Steering system externa! leakage
Foaming milky power steering
fluid, low level and possible
low pressure.
POSSIBLE CAUSE
Loose belt.
Low oil level.
Air in the oil.
Defective hoses or steering gear.
Flow control valve stuck or inopera­
tive.
Loose screw in end of flow control
valve.
Cracked or broken thrust or pressure
plate.
Pressure plate not flat against cam
ring.
Extreme wear of cam ring.
Scored pressure plate, thrust plate or
rotor.
Vanes not installed properly.
Vanes sticking in rotor slots.
Air in the fluid, and loss of
fluid due to internal pump
leakage causing overflow.
Fig. 3B-24~Power Steering System Diagnosis
CORRECTION
Adjust tension to specification
Fill reservoir to proper level.
Locate source of leak and correct.
Bleed system.
Correct as necessary.
Remove burrs or dirt or replace.
Tighten.
Replace part.
Replace pressure plate.
Replace parts, flush system
Replace parts. (If rotor, replace with
rotating group kit), flush system
Install properly. Radius edge to outside.
Free-up by removing burrs, varnish or
dirt.
Check for leak and correct. Bleed
system. Extremely cold temperatures
will cause system aeriation should
the oil level be low. If oil level
is correct and pump still foams,
remove pump from vehicle and
separate reservoir from housing.
Check welsh plug and housing for
cracks. If plug is loose or housing
is cracked, replace housing.