Xantia s2 ABS problems...

[lankytim]

Hi Citroenists.

My 2001 HDi has an issue with the ABS. As the car is slowing down the ABS cuts in at low speed, about 2-3 MPH, causing the pedal to pulsate and braking to be impaired. I thought it could be a dirty O/S/F sensor and ring as I had the hub apart recently and the whole lot ended up covered in grease when I replaced the CV gaiter. I cleaned the whole lot up tonight with WD40 and a scrubbing brush but the fault persists.

Any ideas on what the problem could be?

Tim

[Hell Razor5543]

I would be inclined to clean both front rings and sensors with a decent cleaning alcohol (such as IPA or Acetone) just to make sure, using a tooth brush. The ring teeth need to be clear for the sensor to read then cleanly.

[Mandrake]

Did you take the sensor out when you had the hub out ? Is there any chance the gap between the sensor tip and the teeth is too large now ? From what I've read it's possible to reassemble it with a spacer on the wrong side giving you the wrong gap.

A bit of grease won't affect the sensor as it works based on a magnetic field, but the gap between the teeth and the sensor tip is very critical. Too much gap will reduce the signal level and the signal is also naturally lower at lower wheel rpm thus problems will occur first at low speeds when the gap is too big.

Check the gap very carefully compared to the opposite side.

[citronut]

the other possibility is you damaged the sensor whilst removing and refitting the CV joint in the hub,

what is the condition of the front brake disc's as maybe they are slightly warped/running out of true

[citroenxm]

Just to Echo, it will be either the Air Gap between the sensor "face" and the Ring teeth is TOOOO big.. It should be virtually touching the teeth But not actually touching them... or the ABS ring is rusted, and is loose on either of the front CV joints..

S2 xantias seem to suffer rotton ABS rings more then S1 cars.. They are a heat shrink fit onto the CV joint.

[lankytim]

Thanks for the wealth of info guys! I did indeen remove the sensor then reattatch it to the replacement hub. I didn't see any spacers though! I will remove both front wheels and compare the gaps.

Front brake discs are new and seem to be fine regarding warping or being out of true.

[Mandrake]

The metal shield that shares the same bolt can act as a spacer. I believe it can be put on the wrong side. If its not that check for muck or rust between the faces that might be holding it further away.

Did you change the driveshaft as well or just the hub ? I don't know if its the case but if there are differences in the CV joint outer diameter between different years/models you could have a hub that positions the sensor expecting a large CV joint but only a small one is fitted! Anyone know if this is possible ?

[lankytim]

I didn't change the shaft, just the hub. Anyway, its fixed now! You were correct with the metal shield comment, I had bolted it under the sensor, rather than on top. The brakes now work perfectly. Thanks for all the great advice!