Sagging Is a Nagging Problem

Like your abdomen, a car sags with age. The springs begin to lose their resiliency after years of use, and metal fatigue sets in.

A car can sag a certain amount without any ill effect on your driving.

But at some point, the car will bottom out on hard bumps and the overall handling will become progressively more mushy, prompting a frequent question: Should I replace my springs?.

In years past, manufacturers frequently used leaf springs in the rear suspension system and coil springs in the front.

Today, almost all cars have coil springs all around with highly modified suspension systems.

Because leaf springs were subject to greater corrosion, they often would sag more quickly and more prominently. But coil springs still must bear the weight of the car at all times and eventually will show their age.

The newest and most advanced vehicles eliminate springs by having automatic leveling systems, which use either hydraulic or pneumatic pressure to keep the car at a prescribed height.

These systems can significantly improve corner handling and keep the car at its proper level when carrying a heavy load in the trunk.

But for some time to come, springs will be what keeps most cars suspended.

Although heavier cars have larger capacity springs, these cars frequently have the worst sagging problems.

Rarely do subcompact or compact cars have sagging problems.

Every car manufacturer sets a specification for ground clearance, a measure of how high a car rides when it’s new from the factory. As the springs sag, the ground clearance is reduced.

Unfortunately, in very few cases do the car manufacturers set limits for what is unacceptable. So it is anybody’s guess, including your mechanic’s, about whether half an inch, an inch or 2 inches is too much sag.

(This problem is not unique to car springs. Except for specific safety equipment, like tires and brake rotors, few standards exist for what is acceptable mechanical degradation on cars.)

If a specification did exist, it would help motorists make an informed judgment. Without any standard, motorists are too often sold parts and services they might not need.

I recently received a letter that illustrates the problem. “I have a 1985 Chevrolet Caprice Classic with only 24,000 miles on it,” a motorist wrote. “I went to a big-name tire outlet, and they told me I needed rear cargo coils for $135. They said GM does not put in the quality they used to.

“This sounds like a fast sales talk to me. What is your opinion?”

Without seeing the car, it is hard to judge. But no car should sag after just 24,000 miles.

General Motors set a specification that is easy to check.

A Caprice Classic sedan or station wagon should have about 10.5 inches of clearance from the ground to the rocker panel, measured at a point 24 inches forward of the rear axle (or the center of the rear wheel).

Almost anybody can check that. But what if the clearance is less than 10.5 inches? Experts say that a half-inch is no problem and that a full inch of sag is tolerable. After that, it becomes problematic.

If your shock absorbers are in good condition and you bottom out, you obviously have too much sag.

A number of devices are sold to help separate collapsed springs, but these do little good and seriously degrade the suspension system.