Buick LeSabre 1965 Service Manual page 434

CHASSIS SUSPENSION
SHOCK ABSORBERS 7-7
compression valve assembly. This
tube is completely filled with fluid
at all times. The reservoir tube
provides space for reserve fluid
and for overflow from the pres-
sure tube during operation.
The piston, piston rod and outer
tube are attached to the car
frame, while the pressure and
reservoir tubes are attached as
a unit to the chassis suspension
through the lower mounting. As
the wheel moves up and down with
respect to the frame the chassis
spring compresses or expands,
and the shock absorber is tele-
scoped or extended. This action
forces the fluid to move between
the pressure and reservoir tubes
through small restricting orifices
in the valves. The relative slow-
ness of fluid movement imposes
restraint on the telescoping or
extension of the shock absorber,
thus providing the r e q u i r e d
dampening effect on spring action.
(1) Compression Stroke Oper-
ation. When the chassis spring is
being compressed the shock ab-
sorber is telescoped, causing the
piston to move down in the pres-
sure tube, forcing fluid through
holes in the piston. The pressure
lifts the intake valve plate, allow-
ing fluid in lower chamber to pass
into the upper chamber. As the
piston rod moves downward into
the pressure tube it occupies
space previously filled with fluid
and this displaced fluid is forced
out of the lower chamber into the
reservoir through the restricting
orifice in the compression valve.
On fast or extreme movements
when the fluid flow exceeds the
capacity of the orifice, the spring
loaded relief valve in the com-
pression valve assembly is forced
open to permit more rapid escape
of fluid. The amount of compres-
sion control is governed entirely
by the volume of fluid displaced
by the piston rod, and the resist-
ance to chassis spring travel is
governed by the area of the ori-
fice and the strength of the com-
pression relief valve spring.
(2) Rebound Stroke Operation.
When the chassis spring expands,
or rebounds, the shock absorber
is extended and its resistance is
instantly effective. As the piston
is pulled upward the intake valve
plate seats and fluid in the upper
chamber is forced through slots
in the plate and holes in the piston
to build up pressure against the
rebound orifice plate. As the
pressure increases, the rebound
spring is compressed and the ori-
fice plate leaves its seat to permit
fluid to pass into the lower cham-
ber. As the piston rod moves
upward out of the pressure tube
the space previously occupied by
the rod is filled with fluid drawn
into the lower chamber from the
reservoir. A separate intake valve
in the compression valve assem-
bly opens to permit return of this
fluid.