Why should shocks and struts always be replaced
Unlike some steering and suspension components,
there is no significant difference in wear rates between left and right
shocks or struts. If one shock or strut is shot, chances are its companion
also needs to be replaced.
For front versus rear, there can be differences
in wear rates depending on vehicle loading and usage. Generally speaking,
when front shocks or struts need replacing, so do those in the rear.
Shock absorbers and struts are designed to
dampen spring oscillations as the suspension goes through jounce and
rebound. This prevents unwanted body gyrations and helps keep the wheels
in contact with the road.
The ride control elements inside perform
this task by creating resistance, which in turn transforms the energy
of motion into heat. The up and down strokes of the piston inside the
shock or strut pumps fluid back and forth through metering orifices
in the piston and valve body.
The resistance created by these orifices
helps dampen spring oscillations while limiting body and suspension
motions. The pumping friction heats the fluid and the heat then dissipates
through the shock body into the surrounding air.
After zillions of such cycles, the cylinder
bore, piston and shaft seals eventually wear out. Though original equipment
shocks have improved in recent years, many still may need replacing
in as little as 30,000 miles. With struts, the lifespan is about double
that of a shock.
Problem is, most people do not notice the
gradual deterioration in ride quality until things get really bad. Many
shocks and struts are not replaced as often as they should be. Replacement
is needed if any of the following symptoms are noted: