GMC 1982 Light Duty Truck Service Manual page 351

Certain precautions should be observed when in­
specting shocks for leaks:
• shocks may have glossy paint on them. Do not
confuse this paint with a leak condition.
• a slight trace of shock fluid around the seal cover
area is not cause for replacement. The shock seal is
engineered to permit a slight seepage to lubricate the
rod. The shock absorber has reserve fluid to compen­
sate for the slight seepage.
• shocks are sometimes incorrectly diagnosed as
leakers due to oil spray originating from some other
source. If in doubt, wipe the wet area from and
manually operate shock as described in Step (2).
Fluid will reappear if shock is leaking.
2. Manually Operating Shocks.
It may be necessary with certain types of shock
mountings to fabricate a bracket that can be installed
on a shock to enable a technician to securely grip the
shock when manually operating the shock. See Figure
3C-9 for suggested methods of providing temporary
grip.
This test should help the m echanic to isolate the
following shock defects:
• binding condition internally
• verify leaking shock
• improper or defective valving
(a) If suspected problem is in front shocks, disconnect
both front shock lower mountings and stroke each
shock as follows: Grip the lower end of the shock
securely and pull down (rebound stroke) then push
up (compression stroke). The control arms will limit
the movement of the front shocks during the com­
pression stroke. Compare the rebound resistance
between both front shocks, then compare the com­
pression resistance. If a noticeable difference can be
felt during either stroke, usually the shock having the
least resistance is at fault.
(b) If shock has an internal noise condition, extend shock
fully, then exert an extra pull. If noisy, shock should
be replaced.
Other noise conditions that require shock replace­
ment 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
When air adjustable shocks are being manually oper­
ated, the air line must be disconnected at the shock
absorber.
BENCH CHECKS
The bench checks are recommended if the proper type
hoist is not available to perform the "on vehicle" tests, or if
there is still some doubt as to whether the shocks are
defective. In addition, the bench test allows a more thorough
visual inspection.
Bench check procedures are discussed for three general
types of shocks.
SPIRAL G R O O V E 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 chamber 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 3 C -10)
(a) Holding the shock in its normal vertical position (top
end up), fully extend shock.
(b) Hold the top end of the shock down and fully collapse
the shock.
(c) Repeat Steps (a) and (b) at least five (5) times to assure
air is purged.
Bench Test Procedure
1. This is a comparison type test. If possible, obtain a new
or known good shock with same part number as shock
under test.
FRONT SUSPENSION 3C-9