Chevrolet LIGHT DUTY TRUCK (SERIES 10-35) Service Manual page 296

(b) If shock has an internal noise condition, extend
shock fully, then exert an extra pull. If noisy shock should
be replaced.
O ther noise conditions that require shock replacement
are:
• a grunt or squeal after one full stroke in both
directions
• a clicking noise on fast reverse
• a skip or lag at reversal near mid-stroke
W hen air adjustable shocks are being manually
operated, the air line must be disconnected at the shock
absorber.
BENCH CHECKS
The bench checks are recom m ended if the proper type
hoist is not available to perform the "on vehicle" tests, or
if there is still some doubt as to w hether the shocks are
defective. In addition, the bench test allows a more thorough
visual inspection.
Fig. 3 C - 9 - - G r ip p in g M e t h o d s
THAT WILL FIT THRU
EXISTING HOLE
FRONT SUSPENSION
Bench check procedures are discussed for three general
types of shocks.
SPIRAL GROOVE RESERVOIR
If this type of shock has been stored or allowed to lay
in a horizontal position for any length of time, an air void
will develop in the pressure cham ber of the shock absorber.
This air void if not purged, can cause a technician to
diagnose the shock as defective. To purge the air from the
pressure chamber, proceed as follows: (Refer to Figure
)
10
(a) Holding the shock in its norm al vertical position
(top end up), fully extend shock.
(b) Hold the top end of the shock
collapse the shock.
(c) Repeat Steps (a) and (b) at least five
assure air is purged.
Bench Test Procedure
1. This is a com parison type test. If possible, obtain a
new or known good shock with same part num ber as shock
under test.
2. W ith shocks in vertical position (top end up), clamp
bottom m ounts in vise. Do not clamp on reservoir tube or
m ounting threads.
3. M anually pum p each shock by hand at various rates
of speed and com pare resistance of suspected shock with the
new one.
Rebound resistance (extending the shock) is norm ally
stronger than the compression resistance (approxim ately 2:-
1). However, resistance should be smooth and constant for
each stroking rate.
4. Observe or listen for the following conditions that
will indicate a defective shock:
• a skip or lag when reversing stroke at mid travel.
• seizing or binding condition except at extreme end
of either stroke.
• a noise, such as a grunt or squeal, after completing
one full stroke in both directions.
• a clicking type noise at fast reversal.
• fluid leakage.
To check for a loose piston, completely extend shock
5.
to full rebound; then exert an extra hard pull. If a give is
felt, a loose piston is indicated and shock should be replaced.
3C-9
3C-
down
and fully
(5) times to
LIGHT T R U C K S ER V IC E MANUAL