Shock Absorbers Description; Operation - Pontiac FIREBIRD 1972 Service Manual

3-12 1972 PONTIAC SERVICE MANUAL
SHOCK ABSORBERS
DESCRIPTION
Shock absorbers are hydraulic devices that help to control
the up-and- down and rolling motion of a car body while
at the same time controlling wheel and axle motions. The
car's springs support the body, but shock absorbers work
with the springs to control movements of the body, wheel,
and axle. They do this by changing the energy of these
movements into heat. This energy transformation (damp-
ing) is accomplished by forcing an incompressible fluid
through a system of small orifies (holes) and valves. Shock
absorbers generate enough heat during operation that they
often are too hot to touch after a car has been driven over
a rough road. The hydraulic fluid used in shock absorbers
was developed to withstand these high temperatures as
well as low temperatures encountered during winter
months.
Fig. 3-7 Front Suspension Components
The inner end of the lower control arm is connnected to
the frame with rubber pivot bushings and the outer end to
the steering knuckle with a ball joint.
The inner end of the upper control arm is attached with
rubber bushings to a cross shaft which bolts to the frame.
Shims are located between the cross shaft and frame to
adjust caster and camber to specifications. The outer end
of the upper control arm is attached to the steering
knuckle with a ball joint.
Both upper and lower ball joints have lubrication fittings.
Fixed boot neoprene grease seals protect the ball joints
from dirt and water and act as a grease retainer. The seal
is not serviced. Removal or damage to the seal necessitates
replacement of the complete ball joint assembly. The seal
has a one-way relief valve so that service lubrication can
be performed.
Side roll stability is maintained with a steel stabilizer shaft
(Fig. 3-6). All series have a stabilizer shaft except X Series
-
6 cyl. without air conditioning. It is mounted in rubber
bushings, supported by brackets at each frame side rail
forward of the springs. The ends of the stabilizer shaft are
connected to the lower control arm by short links which
have rubber grommets at both ends to prevent rattle, ex-
cept the A Series handling option (not firm ride) used
plastic grommets.
Coil springs are located between each frame side rail and
lower control arm. Sealed, direct-acting, double-action
shock absorbers are located inside each front coil spring.
Maximum full compression or rebound travel of the sus-
pension is restricted from metal-to-metal contact by rub-
ber bumpers. Bumpers attached to the frame below the
upper control arm or on some models to the upper control
arm cushion rebound travel. Bumpers attached to the
lower control arm cushion compression travel (Fig. 3-7).
There are four shock absorbers on a car; one located near
each wheel. They are direct-acting because of their direct
connection between the car frame (body) and the axle (or
wheel mounting member). They are also double-acting
because they control motion in both directions of the sus-
pension travel. Upward movements of the body are
termed reboundand downward movements, compression.
The rapid movement of the fluid between the chambers
during the rebound and compression strokes can cause
aeration or foaming of the fluid (aeration is the mixing of
free air and the shock fluid). When aeration occurs, the
shock develops lag (piston moving through an air pocket
which offers no resistance). There are two means of elimi-
nating aeration used. One is a spiral groove reservoir tube,
installed as original equipment, which breaks up the air
bubbles in the fluid. The other is a gas filled cell, used for
service replacement, which replaces the free air in a shock
absorber.
Standard and heavy duty shock absorbers are filled with
a calibrated amount of fluid and sealed during production.
Tney are non-adjustable, nonrefillable and cannot
be
disassembled. The only service they require is replacement
if they have lost their resistance, are damaged, or leak oil.
OPERATION
Although a shock absorber operates according to basic
hydraulic principles, it may appear somewhat com-
plicated. Fig. 3-8 gives an easier understanding of how a
shock absorber works by dividing the shock absorber into
four distinct chambers: A-The chamber above the piston,
B-The chamber below the piston, C-The reservoir cham-
ber below the fluid level and D-The air volume in the
reservoir above the fluid level.
When the car wheel strikes a bump, it forces the axle and
bottom section of the shock absorber up toward the body.
This makes the shock absorber sections move toward each
other (called compression) and build up pressure against
the fluid in chamber B of the cylinder tube.