Suspension Alignment; Caster - Pontiac FIREBIRD 1972 Service Manual

FRONT SUSPENSION 3-13
REBOUND COMPRESSION
Fig. 3-8 Shock Absorber
This pressure forces fluid through the intake valve into
chamber A. Because of the space taken up by the piston
rod, chamber A cannot hold all of the fluid from chamber
B and the excess fluid from B is forced through the base
valve into chamber C. As more fluid moves into chamber
C, the air in chamber D is squeezed and the pressure
increases.
When the energy of the bump is used up, the axle starts
down and the shock absorber begins to move apart on the
rebound stroke (Fig. 3-8). When this happens, fluid from
chamber A is forced into chamber B through the rebound
valve. At the same time, the cylinder intake valve opens,
letting fluid from chamber C go back into chamber B.
Because the movement of the piston is slowed by the fluid,
the motion of the car body is also checked.
SUSPENSION ALIGNMENT
Front suspension components are adjusted to a specific
alignment while the vehicle is motionless and at curb
weight and height (see Curb Height chart in Section 0) so
that suspension components can properly function
together when vehicle is moving to minimize tire wear and
maintain desirable steering and handling characteristics.
Steering axis inclination, toe-out on turns and rear suspen-
sion alignment is maintained by design and is not adjusta-
ble.
CASTER
Caster is the forward or rearward tilt of ball joints com-
pared to a vertical line when viewing the vehicle from the
side (Fig. 3-9). Caster is provided to give directional stabil-
ity in the vehicle.
Improper caster will cause very poor steering response
and front wheel shimmy. Caster is adjusted by placing
small steel shims between the upper control arm shaft and
frame support. The shims can be placed either at the front
'or rear of the frame support. Adding shims to the front or
removing shims from the rear of the support will cause the
caster angle to tilt forward (negative caster). Adding
shims to the rear or removing shims from the front of the
support will cause the caster angle to tilt rearward (posi-
tive caster). The thickness of the shims used governs the
amount of caster angle measurement.