Why should shocks and struts always be replaced in pairs?
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:
- A bouncy or uncomfortable ride
- Nose dive when braking
- Excessive body sway when cornering
- Tail squat when accelerating
- Fluid leaks
- Physical damage to the shock or strut itself or its mounting
hardware
- Cupped tire wear
- Indications of bottoming (check suspension stops)
- Vehicle fails a bounce test (more than two oscillations after
rocking and releasing the bumper)
- When the rod on a gas pressurized shock or strut does not extend
by itself (indicating it has lost its gas charge)
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