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1977 PONTIAC SERVICE MANUAL
Fig.
3-9
Checking
Oil
Pressure (Example)
3. Visually inspect for evidence of leakage in the area of
the seal cover (top of reservoir).
4. A slight trace of shock fluid is NOT cause for
replacement as the seal permits some seepage for lubrication
of the piston rod. The shock contains a fluid reserve to
compensate for seepage.
5. Shocks are sometimes incorrectly diagnosed as leaking
due to oil spray originating from some other source. If in
doubt, wipe the wet area of the shock and reinspect after a
brief road test (impractical on fronts). If a true shock leak,
the fluid will reappear.
6. A shock that is truly leaking is easily detected as there
will be evidence of shock fluid around the seal cover and on
down the reservoir tube and shock should be replaced.
BENCH CHECKS
There are two bench check methods for the two (2) types
of shocks:
a. Spiral groove reservoir (exc. firm ride)
b. Firm ride (smooth reservoir)
The reason for separate checks is that certain
precautions must be taken to purge air from the pressure
chamber on spiral groove reservoir shocks. In the case of firm
ride there is no free air and consequently purging is not a
factor.
Spiral Groove Reservoir
These type shocks should be initially exercised before
attempting a bench check. When stored in a horizontal
position, such as new units in stock, an air void will develop
in the pressure chamber. This void can also result due to
handling off the car if the unit is not continuously positioned
vertically with the top end up.
Perform the following exercise to purge air from the
pressure chamber:
Extend in vertical position
-
top.end up.
Collapse in vertical position
-
top end down.
Repeat above steps five (5) more times to make sure
air is purged from the pressure chamber.
Proceed with the actual bench check as follows:
1. Clamp vise on bottom mount with shock vertical in
vise
-
top end up (do not clamp on reservoir tube or mounting
threads).
2. Pump shock by hand at various rates of speed and
observe resistance.
3. Rebound resistance is normally stronger than
compression (approximately 2 to 1). However, resistance
should be smooth and constant for each stroking rate.
4. Compare with a known good shock.
5. It is normal to detect a hissing noise (orifice swish).
The following are considered abnormal and reason for
replacement
:
a. A skip or lag at reversal near mid-stroke.
b. A seize (except at either extreme end of travel).
c. A noise such as a grunt or squeal after completing one
full stroke in both directions.
d. A clicking noise at fast reversal.
e. Fluid leakage.
Firm Ride Shocks
Firm ride shocks use a gas filled cell in the shock
reservoir. This cell takes the place of air in the reservoir. Thus
aeration or foaming of the fluid is eliminated as air and fluid
cannot mix.
The bench check is the same as given in the spiral groove
reservoir with the following exception:
Clamp shock UPSIDE DOWN in vise. If a lag is noticed
when stroked, it means the gas-filled cell has ruptured and
the shock should be replaced.
TIRE DIAGNOSIS
Irregular and/or Premature Wear (Fig. 3-1 2)
Irregular and premature wear has many causes. Some
of them are: incorrect inflation pressures, lack of tire rotation,
driving habits, improper alignment.
If the following conditions are noted, rotation is in order:
1. Front tire wear is different from rear.
2. Uneven wear exists across the tread of any tire.
3. Left front and right front tire wear is unequal.
4. Left rear and right rear tire wear is'unequal.
5. There is cupping, flat spotting, etc.
A wheel alignment check is in order if the following
conditions are noted:
1. Left front and right front tire wear is unequal.
2. Wear is uneven across the tread of any front tire.
3. Front tire treads have scuffed appearance with
"feather" edges on one side of tread ribs or blocks.
Wear Indicators
The original equipment tires have built-in tread wear
indicators to show when tires need replacement. These
indicators will appear as 1/2" wide bands when the tire tread
depth becomes 1/16 of an inch. When the indicators appear
in 2 or more grooves at 3 locations, tire replacement is
recommended (Fig. 3-13).
Radial Tire Waddle
Waddle is side to side movement at the front and/or rear
of the car (Fig. 3-14). It is caused by the steel belt not being
straight within the tire. It is most noticeable at low speed, 5
to 30 mph. It may also appear as a ride roughness at 50 to
70 mph.
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