Brakes Vibrating

[pmj]

Hi, I am not sure if I have an issue or not, my brakes vibrate when trying to stop from high speed only, they only seem to do it on one bit of road, slightly downhill, does not seem to do it anywhere else (not many place that I hit this speed on), but I have checked the pads and there is loads lest on the, the discs look ok, but this is most concerning if I need the brakes in an emergency and I get this as it does take away the performance of the brakes... what else should I be looking at, was thinking of changing the discs and pads any one have a suggestion for a reasonable set better than the standard set up ...?

[jaygemson]

Generally speaking this is caused by hot spots or uneven deposits of material on the disc surface. Through light everyday use the pads don't get hot enough and can end up sweeping away the transfer layer originally created by bedding in. On subsequent brake applications pad material then ends up transferring unevenly, leaving high points on the disc which heat up more quickly and if bad enough can change the structure of the iron in those areas to cementite which appears as dark blobs.

My advice would be to try going through the bedding process again, assuming you have plenty of life left in the discs and pads. If that fails, it may be worth trying to skim the discs. TBH though stock S4 discs and pads are cheap enough, it may be worth simply replacing them for peace of mind.

Some good information about this here:
http://www.stoptech.com/technical-suppo ... ther-myths
http://www.zeckhausen.com/bedding_in_brakes.htm


You're running MRC stage 2 aren't you? Given the weight of the S4 and the additional performance you now have I would suggest a front brake system upgrade. The S4's single-piston floating caliper and one-piece disc/rotor just can't dissipate heat quickly enough. Bang per buck I'd recommend the RS5 setup, consisting of bigger 2-piece discs and 8-piston Brembo calipers. It's a straight swap, and whilst expensive is a lot cheaper than most BBKs out there: http://www.ebay.co.uk/itm/Audi-R8-RS5-R ... 0739&rt=nc

I can vouch for these after having just fitted some to mine:

[pmj]

Thanks for the advice. Makes sense reading this and the links. I agree with the upgrade but cannot pay £2.5k for a front brake upgrade no matter how good they are especially if this is just for fast road driving However replacement discs pads and brake lines are almost a certainty given the issue I have

Again thanks