Chevrolet Light Duty Truck 1973 Service Manual page 180

3-6 FRONT SU SPEN SION
BALL JOINT ASSEMBLY
Fig. 5—Ball Joints-Typical
body while at the same time controlling wheel and axle
motions.
The vehicle's springs support the body, but shock
absorbers work with the springs to control movements of
the body, wheel, and axle for smooth driving. This is
accomplished by changing the movements of the spring
(kinetic energy) into heat energy. Therefore, a shock
absorber may be considered as a damper to control the
energy stored up by the springs under load.
Operation
A shock absorber is sometimes compared to a water
pistol. Of course, there are many steps between a water
pistol and a shock absorber, but both are damping
devices and both use the same principle—they force an
incompressible liquid through small openings.
There are usually four shock absorbers on a vehicle; one
located near each wheel. They are direct-acting because
of their direct connection between the vehicle frame
(body) and the axle (or wheel mounting member). They
are also double-acting because they control motion in
both directions of the suspension travel. Up movements
of the body are termed rebound and down movements,
compression.
The compression movement of the shock absorber causes
the piston to move downward with respect to the cylinder
tube (figure 7), transferring fluid from chamber B to
chamber A. This is accomplished by fluid moving
through the outer piston holes and unseating the piston
intake valve. Since all the fluid in chamber B cannot pass
into chamber A due to the volume of the piston rod, the
fluid equivalent to the rod volume is discharged out of
the compression valve into chamber C of the reservoir
with a corresponding compression of the air in chamber
D. Compression control is the combination of load due
to the compression valve and of load due to the piston
intake valve.
The rapid movement of the fluid between the chambers
during the rebound and compression strokes can cause
SEAL COVER
SEAL
SEAL SPRING
ROD GUIDE
REBOUND SPRING
PISTON NUT
CYLINDER END
COMPRESSION
VALVE CAGE
RELIEF VALVE
Fig. 6—Major Components of a Shock Absorber
C O M PR ES S IO N FORC E
B LOW O FF PORT
Fig. 7—Shock Absorber Compression Schematic
aeration or foaming of the fluid (aeration is the mixing
of free air and the shock fluid). W hen aeration occurs,
the shock develops lag (piston moving through an air
pocket which offers no resistance). Two means of
eliminating aeration are utilized. One is a spiral groove
reservoir tube, Figure 8, which breaks up the air bubbles
in the fluid. The other is a gas filled cell, Figure 9, which
replaces the free air in a shock absorber.
UPPER MOUNT
CYLINDER TUBE
BASE CUP
LOWER MOUNT
t
FLUID
(H YD R A U LIC )
A IR OR
GAS FILLED
CELL
PISTON
IN TA K E
V A LV E
B LO W -O FF
V A LV E
PISTON H OLES
FLU ID
(H YD R A U LIC )
HIGH VELO C ITY
ORIFICE
LO W V ELO C ITY
ORIFICE
BLOW O FF
VA LV E
LIGHT DUTY TRUCK SERVICE MANUAL