Pontiac Fiero 1988 Service Manual page 150

STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS 3-9
having acceptable ride quality. Both strut
dampeners/shocks should provide the same
feeling of resistance.
If there is much difference between the right and
left rear shocks, go to the next step.
5. Support the rear axle at least enough to unload
the shock mounts.
6. Disconnect the lower shock mountings. Stroke
the shocks at various rates of speed, through
maximum travel in both directions. Compare the
two sides for rebound and compression
resistance. Rebound resistance is normally
stronger than compression (about 2 to 1). The
right and left shocks must feel comparable.
Differences between front and rear are normal. If
in doubt about the condition, compare with a
shock known to be good.
Noisy
For struts, follow Steps 1 through 3.
1. Check all mountings for proper torque. A loose
mounting will cause a noise.
2. If all mountings are intact, bounce the car as in
Step 4 (weak) to isolate the suspected unit.
3. If practical, ride with the owner to be sure you
understand the complaint, before proceeding to
next step.'
Leaks
1. Fully extend the strut/shocks (wheels
unsupported) to expose the seal cover area for
inspection.
2. Look for signs of leaks in the seal cover area.
3. A slight trace of fluid is NOT cause for
replacement; the seal permits some seepage to
lubricate the piston rod. There is a built in fluid
reserve to allow for seepage.
4. A leaking strut dampener/shock can easily be
found because there will be fluid around the seal
cover and an excessive amount of fluid on the
strut dampener/shock. A leaking strut
dampener/shock must be replaced..
BENCH CHECKS
Strut Dampeners and Regular Shock
A b s o r b e r s
(Standard and Firm Ride)
Regular strut dampeners/rear shocks use a
gas-filled cell in the fluid reservoir. Aeration or
foaming of the fluid is eliminated, as the gas and the
fluid cannot mix.
Proceed with the actual bench check as follows:
1. Clamp the strut dampener/shock UPSIDE
DOWN in the vise. Do not clamp on the reservoir
tube or the mounting threads. If a lag is noticed
when it is stroked, it means the gas-filled cell has
ruptured and replacement is necessary.
2. Pump strut dampener/shock by hand at various
rates of speed and note the resistance.
3. Rebound resistance normally is stronger than
compression resistance by about 2 to 1. However,
the resistance should be smooth and constant for
each stroking rate.
Compare with a strut dampener/ shock known to
be good.
It is normal to hear a hissing noise. The following
symptoms are abnormal and are reason for
replacement.
A. A skip or lag at reversal near mid-stroke.
A seize (except at either extreme end of
travel).
A noise (such as a grunt or squeal) after
completing one full stroke in both
directions.
A clicking noise at fast reversal.
Fluid leakage.
TIRE DIAGNOSIS
B.
C.
D.
E.
Irregular a n d P r e m a t u r e W e a r
Fig.
13
Irregular and premature tire wear has many
causes. Some of them are: incorrect inflation pressures,
lack of regular rotation, driving habits, or improper
wheel alignment. If wheel alignment is reset due to a
tire wear condition, always reset toe as close to zero
degrees as the specification allows.
1. WEAR INDICATORS
B i
m
Fig. 1 2 Tire W e a r Indicator
If the following conditions are noted, rotate the
tires:
• Front tire wear is different from rear.
m Uneven wear exists across the tread of any tire.
• Left and right front tire wear is unequal.
® Left and right rear tire wear is unequal.
Check wheel alignment if the following
conditions are noted:
m Left and right front tire wear is unequal.
• Wear is uneven across the tread of any front tire.
• Front tire treads have a scuffed appearance with
"feather" edges on one side of the tread ribs or
blocks.