Shock absorbers keep your car's tyres flat against the surface of the road, providing even pressure so the tread wear remains consistent. Another function of the shocks involves absorbing vertical up and down impacts and movements for the rear axle and front end suspension. Without shock absorbers, the vehicle's ride would be noticeably rough and jarring, causing other components to wear much faster than normal. Shock absorbers exhibit numerous signs when they have weakened or failed.
Shock absorber height
Fully extended and with fully functioning seals and pistons, shock absorbers have a predetermined height, positioning the vehicle at the proper distance from the ground. All sides of the vehicle should remain within about 10 cm (a few inches) of each other if the tyres have the exact pressure and the front end suspension parts have no damage or wear. Any noticeable deviation in height can indicate a weakened or leaking shock tube.
Excessive bouncing or rebounding when the vehicle rolls over driveway lips or bumps can point to shock absorbers that have lost their dampening effect. Trapped hydraulic fluid inside the shock cylinder slows the vertical movement of the shock piston; when the seals have leaked or when McPherson strut springs have weakened, there is a definite bounce to the car, a sure sign that the shock absorbers must be replaced. A simple rebound test can be performed by shoving down hard on the front or rear bumper. Generally, a car that rebounds more than twice has a shock absorber issue, indicating replacement.
Any visual leaks around the shock body tube, either at the top or body of the shock absorbers, indicate that the seals have worn or split. As a result, there is a loss in hydraulic fluid, and all dampening effect has disappeared. Oil will be plainly visible on the shock absorber body along with grime and dust.
Loud clanking or knocking noises coming from the undercarriage, when driving over bumps or curves, may indicate a broken shock mount. Sometimes the bolts break, and the shock tube disengages completely, causing that side of the vehicle to sag. A broken shock absorber can also produce a scraping or grating noise.
Worn shock absorbers cannot keep the tyres firmly planted on the road surface. With worn shock absorbers, the tyres have a tendency to wheel-hop or skip, and at high speeds this causes chunks of tyre to be torn from the tread. The tyre wear pattern resembles cups or "scalloping," where the tread appears wavy all around the circumference. This wear pattern specifically points to worn shock absorbers since no other component causes such abnormal tyre wear.
Excess lean and suspension noise
If the vehicle leans excessively into a tight or gradual turn, this means the shock absorber cannot maintain its height and has lost the ability to carry the frame's load. Noises, such as creaking and groaning, can mean other suspension parts are bottoming out (touching or grazing the frame), and this can be a sign that the shock absorbers have lost their strength.
- "Auto Repair Shams and Scams"; Chris Stevenson; 1990
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