GMC 1976 ZEO 6083 Maintenance Manual page 539

when the front wheels meet the wheel stop, or when
the wheel movement is otherwise blocked by a curb
or deep sand or mud. The pump is equipped with a
pressure relief valve. The relief valve is contained
inside the flow control plunger (13) . When the pres-
sure exceeds a predetermined pressure, (greater than
maximum system requirements) the pressure relief
ball (14) opens, allowing a small amount of oil to
flow into the bypass hole (5). This flow of oil passing
through the pressure relief orifice (11) causes a pres-
NOTE : The following diagnostic procedures ap-
ply to the steering system with the exception of
the steering column (For steering column trou-
ble diagnosis see "STEERING COLUMN"
later in this section.)
LEAKAGE CHECK
The purpose of the diagnostic procedure is to
pinpoint the location of the leak . The method ou-
tlined in this manual can be followed to locate the
leak and repair it .
In some cases you will be able to locate the leak
easily . However, seepage type leaks may be more
difficult to isolate . For seepage leaks, the following
method is recommended .
a. With the vehicle's engine off, wipe the com-
plete power steering system dry (gear, pump, hoses,
and connections) .
b . Check oil level in pump's reservoir and
adjust as directed in service manual .
c. Start engine and turn steering wheel from
stop to stop several times. Do not hold in corner for
any length of time as this can damage the power
steering pump . It is easier if someone else operates
the steering wheel while you search for the seepage.
d. Find the exact area of leakage.
e. Replace seal, fitting, gasket, or component
as necessary to stop leak .
An overfilled pump reservoir can be a cause for
leakage complaint . The oil in the steering system
expands as heated during normal usage. If overfilled
the excess is forced through the breather cap hole
TROUBLE DIAGNOSIS
STEERING 9- 7
sure drop and resulting lower pressure on the bottom
end of the control valve (9).
The pressure unbalance then causes the valve to
compress the spring (10) allowing the major portion
of the oil to bypass into the intake chamber (from 3
to 6) in the same manner as is accomplished by flow
controlling . Relief pressures are usually between 750
and 1450 psi depending on the vehicle requirements .
and may be sprayed over the engine by air blast.
Operate the engine and steering system until normal
operating temperature is obtained. Remove the
reservoir cap and check the graduated level on the
dipstick . Adjust the oil level as required .
Seepage at the hose connections can be a cause
for leakage complaint and can be due to loose con-
nection nuts . If leakage is observed at the hose con
nections, and the nut is not cross threaded, tighten
the nuts at the gear to 30 foot pounds .
The nut at the power steering pump should be
tightened to 40 foot pounds (maximum). If tighten-
ing to this torque does not stop the leak, refer to the
diagnostic chart.
If either the return hose or the pressure hose
leaks, replace the hose .
SEAL REPLACEMENT
RECOMMENDATIONS
Lip seals, which seal rotating shafts, require spe-
cial treatment. This type of seal is used on the steer-
ing gear at the pitman shaft, at the stub shaft, and on
the drive shaft of the pump . When leakage occurs in
one of these areas, always replace the seal or seals,
after inspecting and thoroughly cleaning the sealing
surfaces . Replace the shaft only if very severe pitting
is found . If the corrosion in the lip seal contact zone
is slight, clean the surface of the shaft with crocus
cloth. Replace the shaft only if the leakage cannot be
stopped by smoothing with crocus cloth first.
Housing or Cover Seepage-Both the power
steering gear and pump assemblies are leakage
checked before shipment . However, occasionally oil
seepage may occur from the gear or pump other than
the seal areas. If this type of leakage is found, replace
the leaking part .