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I have K-Sport 8-Pot fronts on my RS4 B5 and for many months now they have felt and stopped like they could stop a freight train....

Anyway, recently I have an issue, where I percieve that there is significant travel of the brake pedal when I brake sometimes, maybe I am going mad, but I think when I stamp on the brakes they respond brilliantly with a sharp bite and the front dips big time, BUT if I press the pedal slowly it feels like there is a huge amount of travel....and somtimes when I get real low on the pedal a major grind/vibration comes back through the pedal....not all the time though...

Any Ideas?

This sounds very much like a broken ABS reluctor ring on the driveshaft, mine is doing just what you say and its broken a rear one. Unable to pick it up on Vagcom either.

Thanks for answering, I have come to the same conclusion by researching on the net and looking up my symptoms. I will have a look this weekend to check it out. I was just about to post but you beat me to it!!

Thanks!!!

I have read somewhere that Vagcom specifically does not pick up this fault.

No diagnostic equipment picks it up, I have tried 3 different machines including a VAG one.
Pop off the wheel and remove the big bolt in the centre of the hub/disc, usually a 14mm allen key. Then you can push the driveshaft out far enough to be able to see the ABS ring from the rear of the hub where the driveshaft fits in. Turn the brake disc slowly while looking at the ring for a crack. Generally its the rear ones that go, i got one on ebay for under a tenner.

Thanks! I will check the rear ones first then!

Do you need to heat up the new one to pop it back into place? I am not sure how they are fixed into place on Audi's you see.

Yes, you will need to remove the driveshaft, clean up the ring location as best you can then heat the new ring and gently tap it into place.

Ok thanks again, you have been most helpful!

I am looking forward to the weekend now, I swore my days of p!$$ing about with cold cars on a cold day with numb fingers on the roadside were over....