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While in having the damppers replaced recently the brake warning light came on. I was told that although the pads had plenty of life left in them, the sensoor was being triggered by the lip that was developing on the brake discs outside the swept area.

What would be the normal response to this? Is it generally possible to just have the lip machined off, and get a good chunk more life out of the rotors, or is this normally a sign that it's time to replace discs and pads together?

It's the original set (57 reg car, mine from new, 19k miles, never been on ttrack), so they've done OK i nterms of years, but not really in terms of age, and I'm not particularly keen to just give Auudi £1,300 pound if there are other solutions just as good and less expensive.

If the discs do need to go as soon as this happens, do people generally go with OE ones, or are there better alternatives out there?

Either get the set on skimmed to take the lip off (I suspect there will still be some life left in them) or get new ones. OEM can be found cheap on E-Bay or through the traders on here or you can get a set of skimmed ones to do a straight swap. JHM do alternates (although have to get them from the US) and Mintex but IIRC the mintex ones are more than the OEM ones. Other option is to fit Phaeton front discs, same size but plain discs and 50%+ less than OEM.

Eh?
How can the sensor wire (which are near the middle of the pad) be triggered by the lip outside the swept area?

adsgreen wrote:Eh?
How can the sensor wire (which are near the middle of the pad) be triggered by the lip outside the swept area?

I don't know. I was told that the pads have plenty of life left, but that there's a sensor that measures distance at the top of the pad, and that this was being trigggered by the lip. Is this not the case?

Does anyone know the minimum disc thickness, and anyone in London that can do the joob (i.e. take the car in, remoove te brakkes, skim them, and re-fit)?

Hmm.. Not convinced. All the pad sensors I've ever seen were near the middle or bottom of the pad. Nowhere near the edge to cause a false reading from the disc lip.

Worth asking them to get some exact caliper measurements of pads and discs as this will answer it for you. Also worth checking the fluid as you never know (can't recall if the RS4 distinguishes between a worn pad sensor and the fluid level).

You shouldn't need to get the lip ground off midway through the discs life...

No it doesn't so the pad warning light will come up whether for low fluid or pad warning. Like ads says the actual sensors are embeeded in the centre of the pads so a lip shouldn't make any difference. It may even be that the wire is exposed / wet and occassionally goes off? Mine does at present.