Shock absorber boots & bump stops for your car

Protecting the suspension strut: dust boot & rubber stop

The suspension of a car is a complex mechanical system subject to high strain. Nevertheless it must always function perfectly, its functionality being supported by permanent lubrication. In order to protect it most effectively from damage, the dust boot (dust cover, dust sleeve) and rubber bump stop are used.

Protecting the drive shaft on the gear side

The dust boot envelops the plunger rod of the shock absorber at the cylinder, preventing dirt from the road to penetrate the inner shock absorber via its gasket ring. The dust boot is MOT-relevant and cannot show any damage. Another name for the dust boot is the "dust bellows".

Last resort in case of faulty damping: the rubber stop

The rubber stop is located within the coil spring of the suspension strut. This is the ultimate damping element in case the suspension plunges so deep that shock absorber's and spring's effect are completely used up. This happens in the following situations:

• failure of the shock absorber
• a snapped spring
• driving too fast on a bumpy terrain
• driving over high obstacles too fast.

The rubber stop protects only against excessive damage. If the car bumps audibly when jouncing, the shock absorber and springs should be checked at the first occasion. In spite of the rubber stop, the suspension strut is likely to have sustained damage.

Dust boots and rubber stop: defects

The dust bellows is a wear part with limited life span. Over time the rubber ages and embrittles, developing cracks. The dust boot is now up for replacement. Repair is not possible. In order to replace the dust boot, the suspension strut must be completely disassembled and dismantled. This is not too difficult on the rear axle: the car is jacked up and the complete suspension strut is simply removed. It is opened with the central bolt and taken apart into:

• coil spring
• bellows
• rubber stop
• impact spring.

On the front axle this is a rather complicated repair as several components around the wheel, brake and steering linkage have to be removed as well. After installation of the dust boot and the reassembly of the entire system unit, the tracking has to be realigned. Once disassembled, the dust boot and rubber stop are very easily removed from the coil spring and replaced by new components. The steering linkage is subject to high strain and therefore all components should be thoroughly checked on occasion of dust boot replacement. This particularly applies to:

• the wishbone
• the ball joint with tie rod
• the axle boot at the wheel
• the brake unit.

When replacing the dust boot, you save yourself an awful lot of work by replacing all other components approaching their wear limit. Evidently, you should check the shock absorber prior to its re-installation. When it makes a "glugging" sound when it is compressed or oil is escaping, it is no longer fit for use and must be replaced.

Safety comes first!

Removal of the shock absorber on the front axle requires compression of the coil spring. No other tool except the professional spring compressor can be used for this. It is known for a fact that most lethal accidents of DIY'ers occur as a result of amateurishly compressed coil springs. The spring compressors of today are cheap and of adequate quality. Therefore there is no reason to take any risk on this point. Equally important is correctly jacking up the car. If no lifting platform is available, a jack stand is the only tool enabling safe repair underneath a car. These tools cost ca. 25 EUR (± £22) per pair in good quality. In combination with a high-quality hydraulic jack, the DIY'er can attain adequate results for every repair underneath the car.

Always replace together with the shock absorber!

Vice versa you save yourself a lot of time and trouble when these cheap components are replaced on occasion of shock absorber replacement. Replacing a shock absorber requires removal of the dust bellows and rubber stop anyway. It follows that replacing these components by new ones does not cause any additional work when re-installing the suspension strut.

Rubber stop and dust boot: costs

Both these components are usually sold as a set. Prices of a single rubber stop start at 10 EUR (± £9). A dust boot costs ca. 6 EUR (± £5.30). Buying them as a set is cheaper. When purchased in a suspension strut repair set including shock absorber element they are even cheaper.