ABS Kicking in early - S4

[michaelg1001]

Good morning chaps

This has been bugging me for a few weeks now, when I pull up to a junction or roundabout etc, the ABS seems to kick in and brake really sharply just as I'm coming up to a stop.

From what I've read, this seems to be a broken ABS ring, however on measuring the wheel speeds yesterday through VCDS, there didn't appear to be any fluctuation between the speeds of each wheel when travelling in a straight line.

I've got no warning lights on the dash at all, could this just be an ABS sensor rather than a ring?

 

[Blue_Thunder]

I had this on my old car. I also tried a number of times on Vagcom to check the wheel speeds and never saw a variation. But sure enough, when I dismantled the car I found a rear ABS ring split. Trying to link to a photo, but for some reason ASN doesn't seem to like cut&paste of links on my phone.

Someone suggested I should have logged the wheel speeds using the VAG-Scope option, as even tiny variances would be shown.

 

[aragorn]

yep it'll be a broken ABS ring.

Sometimes you'll see it on VAGScope, but not always.

 

[michaelg1001]

Cheers guys.

What are these like to replace? Can the rings themselves be replaced or is it the whole CV?

 

[aragorn]

You can get the rings on ebay.

Not replaced one myself, probably need to heat it up to press it onto the CV.

 

[Kevinb5]

I had the same symptoms on my FWD,turned out to be grease on the ring from not being careful refitting the disc.

 

[Chriscooke]

If it's the same as on the tqs I had similar symptoms after refreshing my breaks and it turned out to be a dislodged abs sensor.

 

[michaelg1001]

If it's the same as on the tqs I had similar symptoms after refreshing my breaks and it turned out to be a dislodged abs sensor.

I'll check that out first, I don't know whether it's purely coincidental that this started happening around the same sort of time I had the front arms replaced, so the garage that did it could have possibly knocked the sensor when disassembling or assembling.

I'll be having the front brakes off soon anyway to put my B7 A4 brakes on (I say soon, they have been waiting a fortnight already!) so I'll hopefully at least diagnose which corner and what the fault is.

 

[Chriscooke]

It's simple to check, for the fronts you just need to put the car on full lock and give it a reach around

 

[michaelg1001]

Would this be the ABS ring should I need one?

http://www.ebay.co.uk/itm/SENSOR-RI...386?pt=LH_DefaultDomain_3&hash=item2ed2fa3462

Can't see any that say S4 but I assume all of the quattro ones are the same?

I'm going to have a quick check of sensors tomorrow, is there any on the rear that I need to worry about?

 

[spartacus 68]

Did the same job a few years ago and it is possible to fit a new reluctor ring (ABS toothed ring). http://www.audifans.net/ftopicp-245802.html

I bought from here. Wasn't bothered about the cost as I'm not planning on doing it again, and given its a safety item I'd rather not cut corners. S4 reluctor ring at the bottom of the page: http://www.reluctorrings.com/cars/audi

 

[michaelg1001]

Cheers spartacus, that's a big help

 

[aragorn]

I think the rings for sale only fit the rear.

The front ones dont really fail.

And yes, the rear has sensors, theres one on each corner.

 

[michaelg1001]

Well I'm doing the rear control arms and eccentric bolts this weekend all being well, so I might get a ring ordered and hope I can do it there and then.

 

[Mad Cow]

Before you go ordering parts try blasting out the area between the tone ring and sensor with brake cleaner and compressed air. Sometimes it's as simple as gunk built up on the sensor.

 

[michaelg1001]

Never got round to looking into this, spent so long trying and failing to do the arms.

 

[mojocvh]

Hmm I'm getting intermittent abs yellow with associated triple chime sometimes goes off weeks at a time but then seems to return when front nearside finds a pothole or road debris (grrrr) what would be the best way of tracing this? I wonder if it could be the bumps or sudden shocks affecting the abs pump unit or is the problem at the wheel???
Hacked off Andy

 

[spartacus 68]

Getting the car scanned should pinpoint it. In my experience the front ABS rings rarely fail, but could very well be damaged sensor. If it's an avant, then the rear reluctor rings can break. If you don't want to get it scanned it's a laborious job to dismantle each drive-shaft and check ABS.