The Suspension Top Mount
The vast majority of cars on European roads use MacPherson struts. A MacPherson strut requires a bearing (suspension mounting kit) to be able to rotate to follow the axle. In order to find the correct preload for the ball bearing and not to jeopardise the comfort setup of the vehicle, vehicle manufacturers specify torques to be maintained on the strut bearing.
For example, the tightening torque for assembling the suspension strut is 35 Nm for various Audi A3 and Golf VI models. For a Renault Twingo II it is 62 Nm, in a Mini Cooper D 64 Nm and in an Insignia Sport Tourer 70 Nm. It is therefore strongly recommended to check the manufacturer’s instructions for every vehicle before installation.
If you use an impact wrench instead of a torque wrench and Allen key to tighten the top nut, you risk not only destroying the thread but also overloading the bearing, which results in a significantly reduced service life. In addition, it is possible that the nut only sits lightly against the bearing and then turns the piston rod in the strut – the damper is then not properly fixed, which is not only a comfort problem, but a real danger!
As such, KYB recommends that suspension mounting kits are replaced every time you replace a shock absorber.
Is Torque ‘in the wrist’?
You often hear that a good technician has the correct torque ‘in the wrist’. Unfortunately, nobody can apply torque accurately from the wrist. The use of a torque wrench or torque / angle wrench is now essential. Technicians should take care to set the torque correctly, in addition, the torque wrench must be gripped in the grip zone so as not to falsify the measurement results. Finally, after the first release of the torque wrench, the screw should not be loaded any further – or, to put it another way; a release click is sufficient.
The KYB Suspension Solutions App (Europe only) provides technicians with the correct torque settings for vehicles they are working on, with the data taken from the vehicle manufacturers themselves. The App is free to download from both the App Store and Google Play. Users can search for the torques settings, as well as fitting instructions, using vehicle details or VIN number.
Never use expansion bolts twice
Another point that is often disregarded when replacing shock absorbers is the screws for fixing the shock absorbers. Even if they seem inconspicuous, more and more often expansion screws are employed here, which must not be used a second time under any circumstances.
This is because the screws are slightly stretched when tightened to their correct torque and therefore achieve a permanent pre-tension which secures the screw connection. Tightening an already stretched bolt a second time puts it under stress beyond its yield point and can cause the bolt to simply shear off – not necessarily directly during assembly, but during operation on the road.
If the packaging / leaflet with the new shock absorbers indicates a torque including the angle of rotation, the technician should note this and check whether there are any new bolts included in the shock absorber box. If it’s in the box, it should be used on the job.
Why is correct assembly so important?
Modern shock absorbers are high performance components. A piston rod completes 1500 – 2500 strokes per kilometre and accelerates up to 14 kilometres per hour. The pressure inside the cylinder is up to 50 bar and can reach up to 120°C. In order to achieve the desired damping performance in this environment, many parameters must be correct; for example, the piston stroke, the viscosity and quantity of the cylinder oil / gas as well as the valve technology. This interaction can be affected by assembly errors.
What are the consequences of not following the guidelines?
This can range from poorer road holding, to a longer braking distance, to premature failure of the shock absorber due to increased wear. For driving safety and customer satisfaction, it is therefore essential to use top quality components from OE suppliers such as KYB and use the correct tools with the correct settings to avoid assembly errors.
For information on the KYB App, to watch vehicle specific KYB fitting videos, or to see suggestions for useful suspension tools for your workshop, visit www.kyb-europe.com