Pontiac FIREBIRD 1972 Service Manual page 258

FRONT SUSPENSION 3-7
TROUBLE DIAGNOSIS (Continued)
ROD OR TUBING
THAT WILL FIT THRU
EXISTING HOLE
Fig. 3-2 Gripping Methods for Manually Operating Shocks
stroke). The control arms kill limit the move-
ment of the front shocks during the compres-
sion stroke. Compare the rebound resistance
between both front shocks, then compare the
compression resistance. If a noticeable differ-
ence can be felt during either stroke, usually
the shock having the least resistance is at
fault.
(b) If shock has an internal noise condition, ex-
tend shock fully, then exert an extra pull. If a
small additional movement is felt, a loose pis-
ton is indicated and shock should be replaced.
Other noise conditions that require shock re-
placement 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
(c) If suspected problem is in rear shocks, follow
the same procedure described for front shocks
(Steps a. and b. above).
NOTE: When air adjustable shocks (Superlift)
are being manually operated, the air line must
be disconnected at the shock absorber.
B. BENCH CHECKS
The bench checks are recommended if the proper type
hoist is not available to perform the "on car" 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 two general
types of shocks. Refer to Figures 3-3 and 3-4.
I. Spiral Groove Reservoir
11. Superlift
I. Spiral Groove Reservoir
The spiral groove reservoir type shock is installed as
original equipment.
NOTE: If this type of shock has been stored or
allowed to lay in a honiontal 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 the shock to
be diagnosed as defective. Topurge the air from
the pressure chamber, proceed as follows: (See
Fig. 3-5).
(a) Holding the shock in its normal vertical position
(top end up), fully extended 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.
a. Bench Test Procedure
1. This is a comparison type test. If possible, obtaii
a new or known good shock with same part num
ber as shock under test.
2. With shocks in vertical position (top end up)
clamp bottom mounts in vise.
CAUTION: Do not clamp on reservoir tube or
mounting threads.
3. Manually pump each shock by hand at variou:
rates of speed and compare resistance of sus-
pected shock with the new one.
NOTE:
Rebound resistance (extending the
shock) is normally stronger than the compres-
sion resistance (approximately 2:l). 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 cond~tion except at extreme
end of either stroke