The suspension strut: function of suspension struts and how to replace them

The suspension strut is an important component of many vehicles with independent suspension. Here, the strut connects the upper point of the suspension to the vehicle body. The car’s suspension strut consists of several components. It houses both the coil spring and the shock absorber of the respective suspension.

In this way, the suspension struts take over the function of the shock absorbers and at the same time ensure the reliable suspension of the vehicle. As a supporting element of the wheel guide, the suspension struts also make an important contribution to the ride comfort and safety of the vehicle. If suspension struts are defective, they should be replaced with suitable spare parts as soon as possible.

What is a suspension strut?

Suspension struts are part of the suspension of many vehicles with independent wheel suspension. Here they form the movable connection between the wheels and the body as a wheel guide. A suspension strut usually consists of several components such as the coil spring and a shock absorber.

Suspension and shock absorber therefore form a unit as a suspension strut. For this purpose, the shock absorber is usually arranged inside the coil spring and acts as a rigid centre of the strut. Upwards, the strut is often supported against the body by a strut mount, which forms a moving point of the suspension.

Not every car has suspension struts, and in some vehicles the component is only present on the front axle or only on the rear axle. Instead of the suspension strut, the shock absorber and spring are then installed separately, for example, or a completely different suspension principle is used.

Suspension struts fulfil many functions

The suspension struts in a car have several tasks as part of the wheel guidance system. Thanks to shock absorbers inside, suspension struts dampen the vibrations and chassis movements that can occur during driving. Here, the piston rod of the shock absorber moves against a resistance while it is guided in a piston.

In addition to their function as shock absorbers, suspension struts have the task of supporting the vehicle body and guiding the wheels. As an important component of the suspension, the strut absorbs part of the forces acting laterally on the wheel guide.

As a combination of shock absorber and coil spring, the strut also has a not inconsiderable influence on the comfort and function of the car. Suspension, steering and braking behaviour are all influenced by the struts. It is therefore important to replace a defective component such as the suspension strut with a suitable spare part as soon as possible.

Defects on the suspension struts

As the central element of the suspension, the suspension strut is subjected to great loads during driving. Here it takes over the function of wheel guidance, and ensures adequate suspension of the vehicle in all driving situations. The integrated shock absorbers, like the coil spring, are loaded every time the suspension compresses.

Sometimes, therefore, a suspension strut breaks down over the life of the car. For example, the integrated shock absorbers can wear out and suddenly lose oil in the area of the seal to the piston. The coil spring can also break or otherwise wear out over time.

This is why the shock absorber breaks down

In addition to the loads acting on the shock absorber and suspension during driving, there are other possible causes for a defective suspension strut. For example, the suspension strut is often located in the direct splash area of the wheel.

Here, the tyre sometimes swirls up dirt and small stones from the road surface. If these hit the shock absorber or the coil spring, the painted surface is damaged, which quickly leads to rust formation. Rainwater and road salt thrown up by the road surface in winter also affect shock absorbers and springs and intensify the effect.

In addition to these influences, stresses caused by driving with a heavy load can also cause a suspension strut to wear out prematurely. Frequent off-road use of the car can also lead to defects in the shock absorbers and springs, making replacement of the struts unavoidable.

Suspension strut defective – these symptoms indicate this

• Ride comfort noticeably decreases
• Noises such as rattling and banging on poor road surfaces
• Vehicle is clearly in a tilted position
• Steering of the car pulls to one side
• Tyres are worn on one side

Change defective suspension struts

If the car’s suspension struts are defective, they should be replaced with suitable spare parts. The exact procedure for changing a suspension strut depends on the structure of the respective chassis. It also makes a difference whether a rear suspension strut or a front suspension strut is to be replaced.

To replace the front suspension struts, the vehicle is jacked up in a vibration-proof manner. Depending on the model, the brake, for example, must be dismantled and the bolts on the chassis loosened. This applies, among other things, to the ball joint screw on the shock absorber or the clamping screw of the guide joint.

The drive shaft often has to be dismantled to replace the shock absorber. After loosening the screws on the shock strut dome and overcoming the resistance of the lower shock strut mount, the shock strut can be manoeuvred out of the wheel housing. The new shock absorber is installed in the reverse order.

Replace suspension strut with defective shock absorber

As a component of the suspension strut, the shock absorber is exposed to particular stresses and can wear out more quickly than other components. Although the shock absorber and spring can also be replaced separately, it can be worthwhile to replace the entire suspension strut if the shock absorber is defective. This is sometimes easier than removing the shock absorber from the strut.

Three practical tips for changing the suspension struts

1. Replace both suspension struts: It is often advisable to replace both suspension struts of an axle, as all parts are subject to constant wear.
2. Replacing the strut bearings: If the strut bearings are already worn out, the replacement of the struts is the ideal time to replace the bearings.
3. Have the chassis measured: If shock absorbers or suspension struts are replaced, it is a good idea to have the chassis measured and the axle geometry adjusted.

Buy a suitable suspension strut used

If the shock absorber or other parts of the suspension element are defective, you should buy an intact suspension strut as soon as possible. Buying used spare parts from car recycling offers many advantages, such as significantly lower prices compared to new parts.

Autoparts24.eu offers a large selection of suitable spare parts for most vehicle models. Thanks to the practical search, you can easily and quickly find all parts for Audi, VW and many other brands. Thanks to comprehensive information on prices and condition, questions rarely arise.