Function of Shock Absorbers
Why shock absorbers are needed
The term shock absorber is actually a misnomer. A shock absorber does not absorb shocks at all. Your car's springs actually perform that function. However, if a spring were left unimpeded, it would continue to oscillate after hitting a bump. Since the springs support the frame, and the body is attached to the frame, the whole car would bob up and down until internal friction in the spring itself caused it to stop oscillating. This would not only be uncomfortable, but unsafe. A car in such an unstable condition would be extremely difficult to control and maneuver.
Early automobile designers recognized the need to damp out these oscillations by controlling spring movement. Because a modern-day shock absorber actually does this job;it damps out oscillations;you may also hear it referred to as a damper, or just a shock, for short.
If your car seems unstable on the road, you should test your shock absorbers. Indications of instability include feeling road shocks, bobbing up-and-down of the car for a long period after hitting a bump, or a general lack of control in handling. Also, any clunking sounds from beneath the car when it hits a bump or makes a turn should lead you to suspect weak or worn shock absorbers.
Shock failure the hidden hazard
Shocks don't go bad all at once. Unlike a tire that goes flat, leaving no doubt something is wrong, shock absorbers lose their ability to maintain vehicle stability over a period of time. Deterioration is gradual.
Because failure occurs slowly, drivers are seldom aware of the differences in handling weakened shock absorbers cause. Since a potentially dangerous situation can develop without your being aware of it, you should take a few minutes every six months to test the shock absorbers in your car.
Before outlining the testing pro-cedure, it is first necessary to understand how shock absorbers work and what can go wrong with them.
1 On compression, when the wheels and the rest of the car are pushed to-gether, the two cylinders are pushed together.
2 On rebound, when the wheels and the rest of the car return to their normal riding position, the two cylinders are ex-tended from compression to the pres-sure-off position.
The upper cylinder of a shock absorber contains a long piston rod, and serves primarily as a dust cover in which the lower cylinder rests. The piston rod ex-tends down through the upper cylinder into the lower one and ends in a piston assembly.
The main shock absorbing compo-nent inside the lower cylinder is a measured amount of hydraulic fluid which does the job of controlling movement.
All shock absorbers work the same way. They are firmly attached to an upper and lower support. The upper support is a stationary part, such as the wheel housing, which prevents the upper cylinder from moving. The lower support is a component of the car's suspension system which is also attached to a spring, such as the lower control arm. Thus, any impact received by the spring will be damped by the shock.
As the wheels hit bumps, the lower cylin-der section of a shock absorber moves with the wheel and is telescoped into the upper cylinder section. As the two cylinders compress, the piston plunges into the thick hydraulic fluid, forcing it through various small orifices. The fluid slows and controls movement. Following impact, shock absorbers extend themselves. The lower cylinder slides from the upper, the piston retracts, and the fluid that was displaced returns to the lower cylinder for storage.
Failure of shock absorbers
There is no way to predict the life expectancy of shock absorbers. And don't be misled into believing that so-called heavy-duty shocks will outlast standard-duty units. The terms heavy-duty and standard-duty do not refer to the length of service shocks provide, but rather to the type of service they are intended to perform. Of course, standard-duty shock absorbers used under heavy-duty conditions will fail much sooner than if they had been used as intended.
Shock absorber life depends primarily on the roads over which you drive. Shocks can provide safe, miles, or they can fail in as little as 5,000 miles. Shock absorber manufacturers generally advise car owners to replace their shocks at 20,000 to 30,000 miles. This advice is intended for people who do not inspect their shocks periodically. The only way to guard against premature replacement, be sure of ade-quate performance, and protect yourself against the hazards of driving with weak shocks, is to inspect them every six months. A shock absorber cannot be repaired. Except for a loose mounting bolt, which may be tightened, when shocks fail, they must be replaced.
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