Shock absorbers which become defective exhibit knocking noises while you are driving. If you are suspicious about your shock absorbers you can hand analyze them. Hold each shock absorber in the installed postion. Extend and compress it. Make note of how smooth the resistance is for the entire stroke of the shock absorber, up and down. It should exhibit uniform resistance. If you happen to have a new shock absorber you can compare it with the installed shock as to its smoothness.

Shock absorbers have been permanently lubricated during their manufacture. Very small leaks can occur and are okay. Shock absorbers cannot be serviced. Defective shock absorbers must be replaced.