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Shock Absorber and Strut Diagnosis

by Larry Carley copyright

shock aborbers, struts, springs

Good ride control depends on the condition of the shock absorbers and struts. Motorists expect safe handling and good ride control from the shocks and struts under their cars, trucks and SUVs. When ride control fails to meet expectations, repairs or upgrades may be needed. Repairs are required when parts are broken, bent, worn out or do not meet specifications. Upgrades, on the other hand, can be made anytime you feel your original equipment shocks, struts or springs are not meeting your expectations.

Some vehicles just don't ride well even when the original equipment shocks and struts are in perfect condition. Many early generation SUVs fall into this category because of their truck-like suspensions. The combination of relatively stiff springs, heavy-duty dampers and large wheels and tires is not one that lends itself to a car-like comfortable ride. This is especially true with short wheelbase SUVs that tend to have a rough, choppy ride.

Many small economy cars also come up short in terms of ride quality and handling performance. The low mass of the vehicle combined with a lightweight strut suspension and rack & pinion steering means there is little to soak up road feedback and harshness. Many small cars also fail to handle extra weight gracefully, and wallow and bottom out when loaded with additional passengers or cargo. A typical complaint from many small car owners is the inability to haul much extra weight.

Performance cars with sport suspensions can also be a source of ride control complaints. A rock hard suspension may be fine for taking hairpin turns at high speeds and generating impressive lateral acceleration numbers on a skid pad, but an overly stiff suspension cannot handle the rigors of tar strips and potholes for everyday driving. Some vehicle owners get tired of a harsh ride. Others may not mind the punishment and may want an even stiffer suspension. They may want even better handling performance and don't mind sacrificing their kidneys in the process.

Diagnosing ride control complaints requires understanding the problem and coming up with a solution. Obvious problems like a broken spring or leaky shock absorber are relatively easy to diagnose and repair. But some ride control complaints may not be easy to identify. When did you first notice a poor ride, sloppy handling or suspension noise? Under what driving conditions do the symptoms occur? Has your vehicle ever been involved in an accident?


A test drive is probably the best way to analyze a ride control problem. What some people may describe as a shimmy, vibration or bouncy ride may have nothing whatsoever to do with shock absorbers or struts. The real problem may be an out-of-balance wheel, bent rim or too much runout in a tire.

It is also important to remember that the suspension and steering are interconnected systems. Problems with one can often affect the other. A weak shock absorber, for example, may do little to dampen bumps, allowing excessive feedback through the steering linkage to the driver. The vehicle may feel like it has a steering problem when in fact the real problem is poor ride control. Likewise, the steering may feel stiff and be slow to return, but the real problem may not be the steering but a bad upper bearing on the front struts.

As you road test your vehicle, note the following during your drive:

How does it ride on a rough road?

How does the suspension take tar strips and bumps?

Is steering effort and return feel normal, or is it sticky, jerky or harsh?

How does the steering feel after hitting a bump?

Does the body lean or sway when cornering?

Does the vehicle nose dive when you hit the brakes?

Does it squat when accelerating?

Are there any unusual noises such as squeaks, rattles or clunks?

Check Ride Height for Weak Springs

Either before or after your test drive, measure and compare ride height at all four corners. More than half an inch difference side to side indicates weak springs or another suspension problem. Better yet, compare the vehicle's measured ride height to the specs in a reference manual. If ride height is at or less than the minimum specified, the springs may be sagging.

Rocking the suspension up and down will reveal weak shocks and struts.


Before you visually inspect the suspension, do a simple bounce test to tell if the shocks or struts are weak. A bounce test is not a very scientific test because it requires a certain amount of judgment. Worn shock absorbers and struts that allow more than one or two gyrations after rocking the bumper up and down and letting go have reached the end of the road and should be replaced. But what about the "marginal" dampers that still soak up some of the bounce, but not as well as new ones? They should probably be replaced, too, to restore like-new handling and ride control.


It depends on their condition. If your shocks or struts are leaking fluid or are obviously weak (bad bounce test), then yes they need to be replaced. Also, the more miles they have on them, the more likely they are wearing out. Frequent driving on rough roads will certainly shorten the service life of any shock or strut.

The Motorist Assurance Program (MAP) has taken a conservative approach on the issue of replacing shocks and struts. The MAP Uniform Inspections Guidelines say shock and strut replacement should not depend on mileage. The guidelines say replacement is required only if a shock or strut piston rod is bent or damaged, if it has broken, damaged or missing mounting hardware, is binding or seized, is severely corroded to the point where it is weakened (struts only), is missing, or has oil "running down the body."

Because of this, new shock absorbers and struts are often sold as ride control UPGRADE products rather than repair or replacement parts. This allows anyone who is unhappy with the way their vehicle rides or handles to buy new shocks or struts without feeling they have been sold something they may not really need.

Because the dampening characteristics of shocks deteriorate gradually over time, the decline in ride control may pass unnoticed. That is why the shocks and struts need to be inspected periodically, and if possible, subjected to a road test to see if they are still capable of doing an adequate job.


According to one consumer survey by Monroe, 70 percent of people think the primary function of shocks and struts is to provide a comfortable ride. Consequently, replacement is seen as a low priority. Only 21 percent of the people surveyed recognized the fact that new shocks and struts can improve handling and ride control.

However, 56 percent of the respondents said the most compelling reason for replacing shocks and struts is to improve vehicle safety, handling and control. The safety aspect of ride control usually does not receive much attention because few people realize its importance. But the condition of the shocks and struts does affect driving safety.

Tests carried out by the Cologne Institute for Traffic Safety in Switzerland found that marginal shocks (50 percent less dampening ability than new shocks) increased the distance it took to stop the vehicle by 21 feet at 31 mph, a 23 percent increase! This occurred because the worn shocks allowed the wheels to hop rather than maintain good contact with the road surface. In other tests, they found that braking while cornering on slick roads with worn shocks could make a vehicle lose control.

Another reason to replace weak shocks and struts is to prolong tire life and the life of other suspension components. Uncontrolled suspension gyrations cause constant changes in camber and toe. This scrubs rubber off the tires and accelerates tire wear. It also increases motion and friction in the ball joints, tie rods and control arm bushings too, which over time adds up to wear.


Worn shocks and struts can be replaced with a variety of standard or upgrade options. Heavy-duty shocks and struts generally have a larger piston bore and are a good upgrade option for trucks and SUVs used for towing. Premium gas-charged shock absorbers and struts can make a noticeable improvement in handling and cornering on vehicles that are not originally equipped with such units. For this reason, gas dampers should be recommended for all applications. Special high-pressure gas struts and mono-tube and dual-tube shocks are also available for drivers who want the ultimate in handling performance. Adjustable dampers as well as electronic shocks and struts are also available for applications that require these types of units.



Most shocks are fairly easy to replace, but some struts can be tricky. On older import vehicles that have cartridge-style struts, it's not always necessary to completely remove the struts to replace the cartridges. Most such applications have enough clearance to allow the top of the strut to be swung out from under the fender once the upper mount is unbolted. On some, though, you will need a special spanner wrench or pipe wrench to remove the body nut from the strut. On others, you can replace the cartridge from above with the strut in place once the upper bearing plate has been removed.

When installing a new cartridge in an older style rebuildable strut, about three ounces of ATF must be poured into the strut housing to aid heat transfer from the cartridge. Also, follow the installation instructions regarding the use of spacers or washers under the body nut on rebuildable struts. Differences in height among replacement cartridges make the use of such spacers necessary.

Replacing the struts usually requires realigning the wheels after the new struts have been installed. You can save yourself some work by marking the position of the camber bolts and upper strut mounts before loosening anything. This helps maintain approximate wheel alignment and should lessen the amount of adjustment that is needed.

If brake lines have to be opened to disconnect them from the struts during strut replacement (cutting the brake line mounting ear can sometimes make this necessary), you will have to bleed the brakes afterward.

Always follow standard safety precautions when using a spring compressor (use the correct type of compressor for the application, making sure that the spring is held securely and that the spring is not overcompressed). Also, make sure the spring is properly positioned and seated before the compressor is released. Some auto parts stores can disassemble the original struts for you if you do not have the proper spring compressor. Another option is to buy a "Quick Strut" that is preassembled and ready to install.

When replacing struts, pay close attention to the condition of the upper bearing plates. These support the weight of the vehicle, and are often in poor condition. A bad bearing plate can cause steering stiffness, noise and poor steering return (memory steer). Do not reuse the bearing plate unless they are in perfect condition.

Related items of interest:

Wheel Alignment Guide
Wheel Alignment & Suspension Diagnosis Guide

Alignment Guide is a quick reference computer program for Windows Desktops or Laptops that covers all the basics of wheel alignment and steering/suspension inspection.
Topics include basic toe, camber and caster alignment, causes of various kinds of steering and tire wear problems, and instructions on how to correct these conditions.

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How To Inspect Your Car's Suspension

Floor Jacks & Jack Stands (How to Safely Raise Your Vehicle)

Servicing Air Ride Suspensions

Checking Chassis Ride Height

Steering & Suspension Quiz

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