CAT’s Inside Line: First Line

Steering and suspension assemblies are vital components on the modern motor vehicle. These parts are safety critical and contribute to the effective and economical running of the vehicle.

One of the more common problems that the Audi A4 experiences are the premature failure of the bushes in the multi-link suspension arms. Because the arms are aluminium due to the Audi weight saving programme, it is recommended to replace the complete arm.

To further complicate the issue, the components on a vehicle tend to wear more quickly on the nearside than the components on the offside as it is this part of the road has more potholes, road debris, water and of course has the added danger of the kerb itself! This being so, the temptation is always there to only replace the failed components on the one side only.

Most professional installers know the dangers of replacing parts with worn bushes on one side of a vehicle only. This approach means that under braking or acceleration the vehicle is highly likely to pull to one side, as the worn bush will ‘give’ more than the newly replaced bush, which may possibly cause a serious accident. It is therefore always best practice to replace suspension components in pairs.

First Line – Wheel Bearings

The Audi A4 utilises an ‘Active’ anti-lock braking system (ABS), which uses magnetic ‘poles’ built into an encoder fitted to the rear of the bearing. This encoder is often incorporated into the seal on Gen 1 and Gen 2 bearings. Here, the sensor receives a reference voltage from the ECU (either 5V or 12V depending on the system).

The sensor has an integrated circuit, which amplifies the signal before feeding it back to the ECU. This system has the advantage that a signal (square wave) is generated regardless of whether the wheel is turning or not. This also means that the signal is far more accurate at lower wheel speeds. If a vehicle is fitted with Gen 3 bearings, the ABS system will most likely be incorporated into the hub unit.

Obviously ASB® is used for ABS, but is also used for hill descent control, automatic volume control, traction control, stability control and even for sat-nav systems when the vehicle cannot obtain a GPS signal.

ASB® bearings are generally fitted in the same way as traditional bearings, but there are additional precautions that should be observed for their storage, handling and fitment.

1st generation bearings must be fitted in the correct orientation with the encoded seal facing the sensor. The bearing reference markings are always on the side of the bearing with the encoded seal. If in doubt, use an ASB® detector. In the majority of applications the ASB® encoder faces inboard (towards the centre of the vehicle), but the location of the sensor will confirm this.

In the case of this generation of Audi A4, the front bearing has mounting lugs which locate the bearing into the knuckle and the rear bearing is a 2nd generation hub assembly. Therefore there is no possibility the bearing can be fitted incorrectly.

ASB® bearings must always be fitted using the correct tools for both removal and replacement to ensure that the encoded seal is not damaged.

Ensure the bearing is correctly stored, away from any source of magnetism (>750 Gauss) and any sources of heat or moisture. If any part of the bearing is damaged it should not be used.

ASB® is now in use as original equipment on over 80% of new vehicles produced worldwide and 90% of vehicles produced in Europe. To date over 100 million ASB® bearings have now been produced.

The First Line kits for this vehicle are supplied complete with all required accessories. The supplied bolts are stretch bolts and therefore these must be used and the old ones disposed of.

The First Line Wheel Bearing range includes more than 120 ASB® bearings and this number is constantly increasing.

This post was written by:

- who has written 1178 posts on CAT Magazine.


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