Don't wait until the steering wheel shakes to get new shocks

Does your car have trouble just staying on the road, especially on windy days? Do you sometimes feel as if the roadbed is coming through the bottom of the car?

At highway speed, do the front wheels and steering wheel vibrate so much that you think the old car is coming apart?

With any sort of sharp cornering, does the whole car lean like a tree in a gale?

The bad news is . . . the car's shocks are worn. The good news is, you won't have to trade in your car and look for something else. And fortunately, the replacement cost can be low.

New shock absorbers, including installation and depending on the quality, car size, and type of suspension, should cost about $200, plus or minus $50. That's less than a set of good-quality tires. If you do the work yourself, the cost could be as low as $70 or less.

In deciding which of the many varieties you want, it pays to know how shock absorbers work. To begin with, their purpose is not to absorb shocks, because the springs do that. Shock absorbers dampen the vibration set up in the spring. A more descriptive term might be vibration dampers.

Most passenger cars come from the factory with fairly lightweight shocks, because the makers are selling comfort; in other words, a soft ride. Trucks or 4-wheel-drive vehicles trade comfort for strength. So if most of your driving is to be done on smooth highways, you can get by with a lot less shock absorber than for vehicles with a more strenuous work schedule.

Shocks provide safety and comfort by helping the car's suspension hold the road. Also, they save money by prolonging the life of the car's suspension as well as the tires.

Typically, shocks are trouble-free, and you won't even know they're there. But when they fail, you may begin thinking about a new car. The velvet feel of your once-smooth ride, the steadiness of the wheel in your hands, and the car's ability to hold a straight course, even in a crosswind, disappear. Simply, your car begins to feel worn out.

When you buy a new car, you can reasonably expect the shocks to last for at least 25,000 miles of ordinary driving over fairly decent roads. When they finally do go, they generally do not break but just become less and less effective.

There are a number of clues that will help you decide if your car's shock absorbers are wearing out.

The easiest test is to push down hard on each corner of the car. If the car rises quickly and holds steady, the shock is good. If the car continues to bounce up and down, at least one shock needs replacement. Leaking from a piston-rod seal is another clue, as is a bent piston rod or a broken or sloppy bushing at either end of the shock.

These visual proofs, added to your own experience in handling the car, are all you need to make your decision.

Basically, there are four types of shocks:

Standard-duty shocks, whether regular or premium grade, are intended for driving at normal speeds on well-paved roads. They're not intended for any sustained carrying of heavy loads. Also, they give a soft ride.

Heavy-duty shocks give better control and longer life. If you intend to keep your car as long as possible, or need to drive on rough roads with any frequency, you might consider these.

Spring-type shock stabilizers should be used if you often carry heavy loads in the trunk or frequently tow a trailer. The best of these use variable-rate springs, which you can identify by the coils. The coils are much closer together at one end than the other.

Special high-performance shocks are usually found in sports cars or police vehicles, because of their superior cornering abilities and all-around roadability. With high-performance shocks on your car, you get a firm, less comfortable ride.

Shocks should be replaced in pairs, both fronts or both rears, although about half of all car owners replace all four shocks at one time, even though the front shocks usually wear out first.

If MacPherson struts (a type of suspension) are involved, it isn't recommended that you do the job yourself, although it is possible. With conventional shocks, however, it is not too difficult for the do-it-yourselfer with tools. Ninety percent of the job is getting the old shocks off the car, since they're usually rusted on.

Here are some suggestions:

Use a penetrating oil (applied the night before) on the nuts. Also, you can use heat or a nut splitter.

Don't allow the rear wheels of cars with coil or air springs to hang. Doing so may stretch the brake hoses and can even let the spring slip out of position.

Don't ever grasp the polished shaft of a new shock with pliers. Any nick or scratch will cut through the oil seal and cause the shock to leak.

Do not overtighten or undertighten the shock-shaft mountings. The rubber cushions should not be so tight that they bulge beyond the washers.

When you're through with the job, check to make sure that no shock rubs on any underbody part, such as fuel lines, brake lines, exhaust system, or suspension.

Shock absorbers, perhaps the least expensive of the major renovations you can make to your car, are the most satisfying. A worn shock can make a relatively new car feel old. New shocks, however, can make the getting-older car feel almost like new.