Shock Absorber Bench Test; Diagnosis Of Wheel Bearings - GMC G Service Manual

3C-4 FRONT SUSPENSION

SHOCK ABSORBER BENCH TEST

SPIRAL GROOVE SHOCK ABSORBERS
1. Purge the air from the pressure chamber.
• Extend the shock vertically — top end up.
• Turn the shock over and collapse it vertically —
top end down.
• Repeat the above step five times.
2. Place the shock absorber in a vise with the jaws
clamped onto the shock's bottom mount.
• Shock absorber should be positioned vertically
in the vise — top end up.
• Do not clamp the vise jaws on the shock's res­
ervoir tube.
3. Pump the shock absorber at various rates of speed
and observe the rebound force.
• Rebound force is normally stronger than the
compression force (approximately two to one).
• Rebound force should be smooth and constant
for each stroke rate.
4. Compare with a good shock absorber.
5. If one of the following are observed, replace the
shock absorber.
• A skip or lag at reversal near mid-stroke.
• A seize (except at the extreme ends of travel).
• A noise (grunt or squeal) after completing one
full stroke in both directions.
• A clicking noise at fast reversal.

DIAGNOSIS OF WHEEL BEARINGS

When diagnosing wheel bearing condition, keep in mind
the general condition of all parts during disassembly and
n o n -s p ira l g ro o v e s h o c k a b s o rb e rs
• Purging air from non-spiral groove shock absorbers is
not necessary. The shock absorbers have a gas-filled
cell in their reservoirs (as opposed to the air-filled cell
in the spiral groove shock absorber reservoirs).
1. Place the shock absorber in a vise with the jaws
clamped on the shock absorber's top mount.
• Shock absorber should be held vertically in the
vise with its bottom end up.
• Do not clamp the vise jaws on the shock's res­
ervoir tube.
2. Pump the shock absorber at various rates of speed
and observe the rebound force.
• Rebound force is normally stronger than the
compression force (approximately two to one).
• Rebound force should be smooth and constant
for each stroke rate.
3. Compare with a good shock absorber.
4. If one of the following are observed, replace the
shock absorber.
• A skip or lag at reversal near mid-stroke.
• A seize (except at the extreme ends of travel).
• A noise (grunt or squeal) after completing one
full stroke in both directions.
• A clicking noise at fast reversal.
inspection. Use Figures 1 through 4 to classify the failure,
and follow the recommended repair procedures.