REAR SUSPENSIONS
6
SECTION 14.2
ASTRA HD8Ec
Hydraulic shock absorbers
Figure 4
The hydraulic shock absorbers are of the telescopic double act-
ing type.
These shock absorbers are also defined ”direct acting” since
their braking action is directly performed on the suspension el-
ements without levers.
They are fitted with thermostatically controlled valves, thus en-
suring that there are no noticeable differences in their perform-
ance, even following sharp changes in temperature.
Shock absorbers are divided into three different parts:
1.
the cylinder part located above the piston (always filled
with oil);
2.
the cylinder part located under the piston (always filled
with oil);
3.
the oil reserve, i.e. the compartment between the cylin-
ders (5 and 6) (never completely filled with oil).
During the bouncing stage, i.e. when the shock absorber ex-
tends, the oil pushed by the piston (4) passes through the com-
partment, from the upper part of the piston to the lower part
of the cylinder.
During the compression stage, i.e. when the shock absorber
lengthens and piston goes downwards, the oil located under
the piston passes directly to the upper part of the cylinder.
For oil passing from one part of the piston to the other, a forcing
pressure intervenes acting on the piston and opposing piston
movement thus causing suspension braking.
Noise
This defect, which is often laid to shock absorbers, can have dif-
ferent origins. It is therefore recommended to inspect suspen-
sions carefully, including shock absorber connections to chassis
or leaf spring.
Check whether no shock absorber part is in ”metallic” touch
with the leaf spring or the chassis.
Shock absorber dust protection distortion, due to wheel rota-
tion, or short oil due to accidental leaks, can cause noise; in this
case the shock absorber must be replaced.
Changes in braking effect
A change in the braking effect can take place accidentally.
The decrease of the braking effect can be due to breakage of
internal parts, short oil or jams.
Replace the shock absorber in any case.
