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Suspension Strut Assembly

Zaki Moulvi posted this on Jun 16, 2014

The strut assembly on your car works in tandem with the shock absorbers to give you a smooth, safe ride. While the shock absorbers keep the car from bouncing and dampen the ride, the strut assembly is designed to combat compression. Properly installed, a suspension strut assembly will keep the car riding at its proper level relative to the road and easily support the car’s weight. Most modern suspensions combine the shock absorbing and struts into one unit, as they must be designed and installed to work in concert with one another.

Suspension Strut History

As early as 1909, cars used strut assemblies that largely resemble the systems in use today. Variations on a simple concept were tried on military vehicles and production automobiles throughout the years

In 1949, Earle S. MacPherson designed what is now widely known as the McPherson Strut. This basic design is found, in some form or another, on most modern cars, typically for the front suspension, where its steering pivot design allows for the addition of steering controls. The McPherson strut consists of a lower control or tracking arm, a coil spring, a housing for a shock absorber, and one or more tie-rod arms to control steering on front wheels. 

This system gained popularity in part due in part to the fact that the entire assembly could be installed as one unit on a variety of automobiles from different manufacturers. In the late 20th Century it became the default option for suspension systems. As automobile technology advanced, front and four wheel drive drivetrains added to the complexity of car suspensions, but the basic principles remain the same. 

The first production car to use the McPherson Strut was the Ford Vedette. Several other Ford automobiles followed suit. Many modern high performance car manufacturers still use a very basic version of the McPherson Strut today, including Porsche, Mercedes Benz, and BMW.

In 1956, Colin Chapman of Lotus introduced the Chapman Strut, which while similar to the McPherson Strut had the advantage of using the drive shaft to replace the lower control arm in the system, saving weight and increasing road clearance. As it uses the drivetrain as an integral part of the system, however, it can only be used on the power train axle of the car.

Modern suspensions increasingly employ electronic systems for ride adjustment, stabilization, and sport tuning, but the basic theories underlying their mechanical function remain the same.

Issues, Maintenance, and Repair

Inspecting a car’s suspension should be a part of an annual maintenance routine. Serious problems will typically be indicated by one or more handling problems. A very simple way to check basic suspension performance is to bounce the car at each wheel. The car should resist the downward force, recoil smoothly and completely back to its starting position, and not create any excessive noise.

Other signs that there may be a problem with the suspension strut assembly include excessive bouncing over bumps, uneven wear and tear on one or more tires, excessive nose diving while braking, or poor handling and steering characteristics. Often it is during inspection and maintenance of shock absorbers that strut assembly issues are discovered and it is not uncommon for an issue attributed to one to actually be caused by the other, as they work together in the larger system.

While shock absorbers are relatively easy to change, struts are typically best handled by a mechanic with the proper tools and experience, as the springs in the assembly are under tremendous pressure and can be very dangerous if not handled properly with a spring compression tool.

Typically, suspension components are replaced in pairs, and often it is the case that the entire assembly will be replaced at once, including tie rod arms and other components due to the amount of labor involved in simply opening up the system for access to the parts. 

The home mechanic can order complete, preloaded strut systems for installation on any number of cars. 

Your car’s suspension system is a crucial element of its handling, safety, and fuel economy. Properly installed and periodically inspected, you can expect thousands of miles of service from a strut assembly. Problems should be addressed immediately, as they may affect other components, impair safety, and reduce performance.

Categories: Autowiki Car Systems