SHOCKS

Let's start our discussion of shock absorbers with one of very important point: despite what many people think,
conventional shock absorbers do not support vehicle weight. Instead, the primary purpose of the shock absorber is to
control spring and suspension movement. This is accomplished by turning the kinetic energy of suspension movement
into thermal energy, or heat energy, to be dissipated through the hydraulic fluid.

Shock absorbers are basically oil pumps. A piston is attached to the end of the piston rod and works against hydraulic
fluid in the pressure tube. As the suspension travels up and down, the hydraulic fluid is forced through tiny holes, called
orifices, inside the piston. However, these orifices let only a small amount of fluid through the piston. This slows down
the piston, which in turn slows down spring and suspension movement.

The amount of resistance a shock absorber develops depends on the speed of the suspension and the number and
size of the orifices in the piston. All modern shock absorbers are velocity sensitive hydraulic damping devices - meaning
the faster the suspension moves, the more resistance the shock absorber provides. Because of this feature, shock
absorbers adjust to road conditions. As a result, shock absorbers reduce the rate of:

Bounce
Roll or sway
Brake dive and Acceleration squat

Shock absorbers work on the principle of fluid displacement on both the compression and extension cycle. A typical car
or light truck will have more resistance during its extension cycle then its compression cycle. The compression cycle
controls the motion of a vehicle's unsprung weight, while extension controls the heavier sprung weight.

Compression cycle
During the compression stroke or downward movement, some fluid flows through the piston from chamber B to chamber
A and some through the compression valve into the reserve tube. To control the flow, there are three valving stages
each in the piston and in the compression valve.

At the piston, oil flows through the oil ports, and at slow piston speeds, the first stage bleeds come into play and restrict
the amount of oil flow. This allows a controlled flow of fluid from chamber B to chamber A.

At faster piston speeds, the increase in fluid pressure below the piston in chamber B causes the discs to open up away
from the valve seat.

At high speeds, the limit of the second stage discs phases into the third stage orifice restrictions. Compression control,
then, is the force that results from a higher pressure present in chamber B, which acts on the bottom of the piston and
the piston rod area.

Extension cycle
As the piston and rod move upward toward the top of the pressure tube, the volume of chamber A is reduced and thus
is at a higher pressure than chamber B. Because of this higher pressure, fluid flows down through the piston's 3-stage
extension valve into chamber B.

However, the piston rod volume has been withdrawn from chamber B greatly increasing its volume. Thus the volume of
fluid from chamber A is insufficient to fill chamber B. The pressure in the reserve tube is now greater than that in
chamber B, forcing the compression intake valve to unseat. Fluid then flows from the reserve tube into chamber B,
keeping the pressure tube full.

Extension control is a force present as a result of the higher pressure in chamber A, acting on the topside of the piston
area.