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Strut Your Stuff

Strut replacement bumps the bounce

The history behind the modern strut-type suspension begins in the United Kingdom and could be easily mistaken as a riddle. What do a Scotsman, a Lotus, a spring, and a shock absorber all have in common? The answer is the MacPherson strut suspension, the integral spring and shock absorber arrangement that was pioneered by one, Earl S. MacPherson. As it was that Mr. MacPherson worked for Ford as the head of engineering, the MacPherson strut first appeared under the unibody front fenders of a 1951 Ford Zephyr. The strut was just one part of the entire MacPherson suspension, which not only provided lighter weight but also improved handling by setting the mass of the suspension low on the vehicle.

Integral Unit

The integral strut and spring combination also simplifies and lightens the front suspension by eliminating the need for an upper control arm and ball joint. The spring, shock absorber and wheel spindle are combined into one integral unit. The setup makes much more sense in that it provides savings in manufacturing and in weight; and, as a result, it is used on many vehicles today. Another suspension pioneer, Lotus engineer Colin Chapman, whose suspension and chassis building prowess put his name into the Formula 1 and Indy 500 history books, and cemented Lotus as a performance marque, is credited for putting the same type of setup, Chapman struts, in the rear of a vehicle.

Capture the Shock

The one drawback of the MacPherson strut setup is that when it comes time to replace a worn out shock absorber, the entire strut assembly must be dismantled in order to release the shock absorber section from its location within the spring. With a double wishbone or leaf spring type suspension, the shock absorber can easily be removed without any major hassles, as it is usually not captured by the spring. What's worse is that a good number of components often must be removed just to get to the struts themselves. So it goes.

Simplicity in design and manufacturing can bring complications to maintenance. As with any sticky engineering problem, humans have found a simple solution to replacing the damper inside the MacPherson strut. A tool known as a spring compressor makes things easier. While the spring is held in the steel claws of the compressor, the strut and shock absorber can be easily removed and serviced. The drawback is that the strut assembly has to be removed from the vehicle.

Even easier than using a spring compressor is to replace the entire strut with a new assembly. Instead of removing the used-up shock absorber from the assembly by way of a spring compressor, the entire strut assembly can simply be swapped out. Like a loaded brake caliper, the strut assembly comes ready to install. Yet another advantage of these new units is that as shocks wear out, so do springs, and replacing both as a unit not only saves time and labor, but can also deliver a better ride down the road. This assembly is a fairly recent innovation and is not yet available for every vehicle on the road.

Easy Does It

While all of this may sound easy, replacing shock absorbers in MacPherson struts can be quite an involved process. Great care must be taken whenever the use of a spring compressor is involved. The springs held captive inside the strut assemblies are designed to safely support the weight of the vehicle and passengers over roads that are both smooth and rough. The force required to compress even one of these springs is tremendous, and can cause great bodily harm, in the form of a flying spring, if suddenly released from the spring compressor.

Exercise extreme caution when it comes to using any type of spring compressor if you should decide to service strut assemblies. NEVER use impact or power tools of any type to compress or decompress a spring with a spring compressor. The sudden movement created by an impact wrench can cause the jaws to slip and release the spring.

Work slowly to compress and release the spring. As there are more than a few particular types of configurations of strut assemblies, it is always best to consult a service manual before beginning any type of suspension work on a vehicle.

Another factor worth considering while servicing suspension is that if the shock absorbers or springs of the strut assembly are worn beyond the point of useful service, odds are high that the rest of the suspension components are tired as well. Since disassembly of the suspension is often required to service the struts, that would mean that this is also a good time to inspect and replace ball joints, tie-rod ends, sway bar end link bushings, and the like. Keeping track of the condition of suspension components in your vehicle is the key to maintaining a smooth and safe ride.