GMC 1982 Light Duty Truck Service Manual page 352

3C-10 FRONT SUSPENSION
TYPICAL FRONT SHOCK
ROD EXTENDED
(R E B O U N O K
SHOCK - >
A
COLLAPSED
T
BOTTOM
MOUNT TOP END
DOWN
INVERT.
THEN COLLAPSE
POSITION FOR PURGING AIR FROM SHOCK ABSORBER
Fig. 3C-10-Position fo r Purging Air From Shocks
2. With shocks in vertical position (top end up), clamp
bottom mounts in vise. Do not clamp on reservoir tube
or mounting threads.
3. Manually pump each shock by hand at various rates of
speed and compare resistance of suspected shock with
the new one.
Rebound resistance (extending the shock) is normally
stronger than the compression resistance (approx­
imately 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.
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.
PUACELL OR G E N E TR O N
Pliacell and Genetron are some of the trade names used
to indicate a gas-filled cell in the shock reservoir. The
reservoirs of Pliacell and Genetron shocks are smooth,
compared to the spiral groove type. The cell takes the place
of air in the reservoir. Thus, aeration or foaming of the fluid
is eliminated, as air and fluid cannot mix.
Due to this feature, these shocks should be bench
checked in an inverted position (top end down). If, when
stroked, a lag is noticed, it means the gas-filled cell has been
ruptured, and the shock should be replaced. If no lag is
noticed, the remainder of the bench check is the same as
given in the Spiral Groove Reservoir, Section 1, Bench
Check Procedure.
TYPICAL REAR SHOCK
BOTTOM
MOUNT
SHOCK -
ROD EXTENDED
COLLAPSED
(REBOUND) '
B O H O M
M O U N T \ t - _ = TOP END
■^ c
DOWN
INVERT. THEN COLLAPSE
AIR ADJUSTABLE SHOCKS
This type of shock contains an air chamber like the
spiral groove reservoir type, and must have the air purged
from the working chamber. See Section 1, Spiral Groove
Reservoir. After air has been purged from shock, proceed as
follows:
(a) Clamp lower shock mounting ring in vise in vertical
position with larger diameter tube at the top.
(b) Pump unit by hand at different rates of speed. Smooth
resistance should be felt through the length of the
stroke. Since the units are normally pressurized, the
sound of air bubbles or a gurgling noise is
(c) The remainder of the bench check is the same as given
in the Spiral Groove Reservoir, Section 1, Bcnch Check
Procedure.
BEARINGS AND RACES
BENCH D IA G N O S TIC PROCEDURE
This section describes common types of bearing distress
and their causes. Illustrations are included to help diagnose
the cause of distress and comments are provided to help
make effective repairs.
Consider The Follow ing Factors W hen
Diagnosing Bearing Distress:
1. Note General Condition of all parts during teardown
and examinations.
2. Classify the failure with the aid of these illustrations
where possible.
3. Determine the cause. R ecognizing the cause will
permit correction of the problem and prevent a repeat
failure of the same type.
4. Make all repairs following recommended procedures.
Com m on Causes For Bearing Distress
Include The Follow ing:
1. Improper adjustment or preloading.
2. Mounting or teardown abuse.
3. Improper mounting methods.
4. Inadequate or wrong lubricants.
5. Entrance of dirt or water.
6. Wear from dirt or metal chips.
7. Corrosion or rusting.
8. Overload.
9. Overheating causing tempering.
10. Frettage of bearing seats.
11. Brinelling from impact loads and shipping.
12. Manufacturing defects.
normal.