Abs Coming On At Low Speeds

[John D]

So, had both front shocks & springs replaced by local garage a little while back, and since doing so I get the ABS cutting in sometimes when at very low speeds - like 3-4mph when just coming to a halt.

 

No ABS light coming on at the dashboard so pretty happy that the sensors are OK. However, on inspection of the sensors and ABS rings I can see when spinning the wheels the ABS rings (& hub that they sit on) are running eccentrically somehow. In fact, so much that at one point of a full turn of each wheel the ring is actually contacting the sensor and wearing it, while at the other side of the turn the airgap between ring and sensor is about 4-5mm which I think is too large. It makes sense to me that at higher speeds I do not get a problem as the time over which the sensor is getting an out-of-range signal (either too high or too low voltage presumably) is so short that it does not matter. However, at low speeds the poor signal duration is sufficiently long that the ABS system declares different wheel speeds and sets off the ABS. Well that's my thinking anyhow.

 

Question is, what the heck causes the ABS rings to run eccentrically, and is it anything to do with having the hub assembly dismantled for the shock & spring replacement?

 

Have not gone back to the garage yet on this, want to get better informed first....

[sparky Paul]

I would guess that the abs ring is split somewhere, or otherwise damaged. They are a tight shrink fit onto the CV joints, and any obvious eccentricity must mean that the ring is no longer in full contact with the outer surface of the joint.

 

Replacement ABS reluctor rings are available relatively cheaply, have a look on that well known auction site.

Edited May 30, 2011 by sparky Paul

[John D]

Thanks - had a good inspection yesterday and no cracks or breaks to be seen. However, the CV joint is badly corroded (can gouge lumps off with a screwdriver) so pretty sure now that the problem is corrosion lifting/stretching the ring.

[chrispb123456]

Maybe when the driveshaft/cv joint was refitted into the hub that some rust or debris has got between the mating faces of the cv joint and hub bearing, this could cause the joint to run out.

[cyborg]

Thanks - had a good inspection yesterday and no cracks or breaks to be seen. However, the CV joint is badly corroded (can gouge lumps off with a screwdriver) so pretty sure now that the problem is corrosion lifting/stretching the ring.

Could also be rust stuck to the abs sensor 'magnets' causing intermitant problem.