Chevrolet 1977 light duty truck, Service Manual

Page: 286 / 861

TYPICAL FRONT SHOCK
extend shock fully, then exert an extra pull. If noisy
shock should be replaced.
O th e r noise co n d itio n s th at re q u ire shock
rep lacem en t are:
• a grunt or squeal after one full stroke in both
directions
• a clicking noise on fast reverse
• a skip or lag at reversal n ear mid-stroke
IM PO RTANT: W h e n air adjustable shocks
are being m anually operated, the air line
must be disconnected at the shock absorber.
BENCH CHECKS
T h e bench checks are recom m ended if the p roper
type hoist is not available to perform the “on c a r” tests,
or if there is still some d oubt as to w h eth er the shocks
are defective. In addition, the bench test allows a more
thorough visual inspection.
Bench check procedures are discussed for three
general types o f shocks.
SPIRAL GROOVE RESERVOIR
IM PORTANT: If this type o f shock has been
stored or allowed to lay in a horizontal
position for any length o f time, an air void
will develop in the pressure c h a m b e r o f 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 cham ber, proceed as follows: (Refer
to Figure 3C-10)
(a) Holding the shock in its norm al vertical
position (top end up), fully extend shock.
(b) Hold the top end o f the shock down and fully
collapse the shock.
(c) Repeat Steps (a) and (b) at least five (5) times
to assure air is purged.
ROD EXTENDED
(REBOUND) x
BOTTOM
M O UN T
BOTTOM
M O UN T \
SHOCK
COLLAPSED
TYPICAL REAR SHOCK
DUST T U B E O T
ROD EXTENDED
(REBOUND) '
BO TTO M '
M O UNT
a
SHOCK -«
COLLAPSED
TOP END
DOWN
INVERT.
THEN COLLAPSE
TOP END
DOWN
BOTTOM
M 0 U N T \ ^ ^
INVERT. THEN C O LLA PSE
POSITION FOR PURGING AIR FROM SHOCK ABSORBER
• < >
Fig. 3C-10--Position for Purging A ir From Shocks
Bench Test Procedure
1. This is a comparison type test. If possible,
o b ta in a new or known good shock with same part
n u m b e r as shock u n d e r test.
2. W ith shocks in vertical position (top end up),
clam p bottom mounts in vise.
CAUTION: Do not clamp on reservoir tube or
m ounting threads.
3. M anually p u m p each shock by h a n d at various
rates of speed and com pare resistance o f suspected shock
with the new one.
NOTE: R ebound resistance (extending the shock)
is norm ally stronger than the compression resist­
ance (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 o f either stroke.
• a noise, such as a g ru n t or squeal, after
completing one full stroke in both directions.
• a clicking type noise at fast reversal.
• fluid leakage.
5. To check for a loose piston, completely extend
shock to full rebound; then exert an extra hard pull. If a
give is felt, a loose piston is indicated and shock should
be replaced.
PLIACELL OR GENETRON
Pliacell and G e n e tro n are some o f the trade names
used to indicate a gas-filled cell in the shock reservoir.
The reservoirs o f Pliacell and G e n e tro n shocks are
smooth, c om pared to the spiral groove type. The cell
takes the place o f air in the reservoir. Thus, aeration or
foam ing o f the fluid is elim inated, as air an d fluid
cannot mix.
Due to this feature, these shocks should be bench
checked in an inverted position (top end down). If, when