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)