Shock absorbers don’t last forever, because they’re always in motion. Even on well paved roads, shock absorbers work to smooth out out the slightest irregularities. Bumpy roads demand far more from shock absorbers, and daily driving dynamics also give your suspension a workout. On acceleration, the rear of the vehicle may squat, but the shock absorbers slow the reaction. Similarly, when braking, shock absorbers slow the “dive” effect. The more aggressively you drive, the more wear you can expect in the shock absorber.

Shock absorbers wear out in a couple of ways and the wear may lead to unexplained shaking and shimmying. When internal valves wear out, they offer little resistance and hydraulic damping. Worn external seals can cause a couple of problems. Gas-charged shock absorbers reduce internal foaming, but a leak might release the gas—air bubbles are not resistant to flow like hydraulic fluid is. External leaks can also allow hydraulic fluid to leak, not only making a mess, but eliminating any hydraulic damping effect.

Shock absorbers tend to last 50,000 to 100,000 miles, but this depends much on how and where you drive. You should test every 20,000 miles or so, just to be sure. Aside for looking out for visible fluid leaks, you can bounce-test your suspension. Push down on the corner of the vehicle you’re testing, then release. If the car bounces more than once, it’s time for shock absorber replacement.