The job of the shock absorber or strut insert is to dampen the oscillations or bouncing caused by suspension coils as they pass over bumps in the road. Testing a shock absorber's ability to return to normal is done by pressing downward on the bumper of the vehicle with the suspected shock. Be careful not to damage the bumper.

Shock absorber function.

A good shock absorber will return to its normal place and come to rest. A bad shock or strut would continue to bounce. This is because the weak shock absorber allows the coil spring to continue to oscillate.