Many Peugeot, Citroën and DS models are equipped with rear brake discs that have an integrated wheel bearing. As a result, this type of assembly allows for significant weight saving, since the brake disc also becomes the wheel hub. Blue Print explains how care must be taken when fitting this type of brake disc to the stub axle, as this disc/bearing assembly is also fitted with a multipole reluctor for the wheel speed sensor.

This pre-assembled part also makes replacement quicker and easier for the workshop, whilst eliminating the risk of mounting a bearing with incorrect clearance or seal positioning.

With the old brake disc removed from the vehicle, the wheel speed sensor should be inspected for excess corrosion surrounding the mounting area. It is important to note that any excess metal corrosion can alter the position of the sensor – affecting its functionality. This can lead to direct contact with the reluctor, causing damage to the new brake disc assembly (Fig.1). Subsequently, an increased air gap between the sensor and the reluctor can also occur, resulting in an anti-lock brake system fault – logged as a sensor implausibility signal fault code in the brake control unit.

Therefore, during the installation of a new brake disc it should be identified if the speed sensor is in contact with the multipole reluctor, or if the air gap is not correctly aligned. If discovered to be incorrect, the brake disc and speed sensor should be removed. The sensor seating location should be cleaned of corrosion and - if damaged - the sensor refitted or replaced. With the new brake disc re-installed, and the sensor correctly aligned, a clear 1-2mm air gap between the reluctor and the sensor will be visible (Fig. 2).