The main parts of this suspension unit comprises a long telescopic tube, which incorporates a damper, this is usually fitted with a piston protector to keep out road grit, to protect the piston and seals.
The coil spring is located between the two retaining cups, this is held in place under compression, by the retaining nut, which is secured to the top of the damper piston.
The unit is rigidly connected to the stub axle or hub assembly at the lower end and is pivoted at the top, usually by a top bearing, to accommodate steering movement. The bearing forms part of the strut top mounting assembly, which acts as an insulator as well as a fixing point, between the suspension unit and the vehicle’s body.
The suspension strut top mounting is a bonded rubber bush, which is mounted to the top of the damper and fixes it to the vehicle’s chassis. This is an integral part of the suspension strut assembly. Strut mountings can also incorporate a bearing or a bearing plate that allows the strut to turn with the steered wheels.
The strut mounting acts as a coupling to the spring and shock absorber, connecting it to the body. The damping force is absorbed separately within the mounting, which in turn insulates the vehicle’s body from suspension and road noise.
In the lateral direction, the mounting is designed to be stiffer. This positively influences the driving dynamics, and the steering response, which greatly reduces noise, vibration and harshness from the driveline and suspension. This ensures maximum driver and passenger comfort.
To do this, the strut top mounting has to ensure low-friction and distortion-free movement, of the shock absorber spring during steering and deflection, enabling the road spring to operate without self-aligning torque. Also, it has to locate the shock-absorber spring and form a support surface for full deflection of the shock absorber.
This has to be achieved in a compact design that has been optimised for limited mounting space, and supplied as a sealed unit and to be maintenance free.
During the life of this suspension unit, the damper and spring have to expand and contract millions of time, enduring the stress of all the road surfaces that the vehicle is driven on. This includes unmade and damaged road surfaces, which bring extra stress on this unit.
During any maintenance work that is carried out on this suspension unit, it is common that the shock absorber or the road spring, are replaced because of wear or failure. The strut top mounting is often only replaced as a distressed purchase when the suspension unit is stripped down for repair or only when the driver of the vehicle complains of any excess noise from this area.
The strut top mount bearing race often falls apart or has seized, resulting in a creaking or grinding noise from the suspension, this can lead to the bearing tearing the rubber apart in the mounting.
The rubber itself can deteriorate with age, leading to reduced driving comfort due to noise development, resulting in tight steering or excess play in the steering, unstable handling and reduced driving and braking safety.
The strength of a strut top mounting comes from the properties of the elastomeric material used and metal reinforcement within it. This gives it the flexibility and stiffness that is required. Pictured is a sectioned view of febi part 22639, with the bearing.
When considering replacement of this part rely on tested OE matching quality spare parts from febi bilstein. The entire range for suspension strut top mountings can be found at partsfinder.bilsteingroup.com.
The febi brand is part of the bilstein group, the umbrella organisation for several other strong brands. Further information is available at www.bilsteingroup.com.