Front Discs Warping ( Again )

[Gingers4]

My 07 RS 4 Avant is on its 2nd set of discs in 2000 miles as thet keep warping. Gladly all work has been done through Audi UK Warranty as they appear to be as confused as I am. Last time the system was stripped and hubs and wheels all checked to get to the bottom of the cause. They ended up just throwing another set of discs & pads at it ( 1ST SET ALL REPLACED AFTER 1100 MILES )as they couldnt find anything.
Brakes started juddering again last week and car is booked in again this week.Im sure all will be replaced as customer service has so far been excellent. The car is not driven hard or on track.Iam beginning to lose confidence in the car at all at it has always felt a bit skittish.at the rear. ( IS THIS NORMAL ? ) All dampers are OK as they were checked at last service.
Any thoughts folks as I keep reading how great my car is but so far I just miss my M3.
Any feed back would be great guys & gals.
Cheers.

[neckarsulm]

Short of cleaning mating faces on hubs, and the calipers and performing a fluid change I'd be at a loss.
Are you sure it's not a worn track rod end causing the judder? I suppose you wouldn't get 1000 miles before the juddering started if it wasn't brake related...?
I'd try another dealer, where are you based?

One thing to note is that juddering can also be caused by the rear brakes.

Can the dealer physically see/measure that the discs are warping?

Skittish at the rear and you had an M3? Doesn't sound right to me.

[Ice_Coffee]

The only way I could see this happening is if your brakes are lightly binding, this would cause increased fuel consumption, and your car would not be as free rolling if you take your foot off the accelerator and coast to a stop.

What is your mpg both town and motorway

[Steve_C]

I heard of another guy who had constant problems with his brakes (on a saloon IIRC). In the end Audi agreed to replace them with ceramics and it cured the problem. Might be worth a try if you keep getting issues?

[philipwalker]

Corrosion of the discs is a factor, especially this time of year and with low use cars.

The discs corrode with the road salt used. The car is left for a few days the discs will start to rust. Where the pad area covers the discs, this can cause a high spot/corrosion mark.

[aidanjaye]

But corrosion caused by salt / weather "normally" will clear after a few miles.

With regards handling (rear end) - check tyre types, pressures etc. From experience, rear end of RS4 feels more planted than M3. The only time I feel the back end is nervous is under extreme heavy breaking - then it feels like it wallowing at the back.

Hope you get it sorted soon ....

[adsgreen]

There's a few thing that it could be
- manufacturing defect. This isn't likely at the best of times and given you've had two replacements then it's incredibly remote.
- The bell hub is faulty / misaligned
- the discs have been fitted badly or the fixing screws tightend in the wrong order "pulling" the disc out of line.
- Disc Thickness Variation - this is the most likely given how quickly they are failing.

I'm not criticising and please be open minded but it is worth evaluating how the brakes are being used. You highlight they are not used hard and this actually can contribute to the DTV problem.
Discs are not perfectly flat but have microscopic high and low points. if you only ever use a light pressure on the brakes then it's only the high points that get in contact with the pads and so these heat up. When up to enough temp the pad material will begin to transfer to the disc as designed but in this example only to the high points. This makes the high points even higher and eventually high enough to cause a noticable judder. This is identical in feel to a warped disc (as to all intensive purposes they are now).

Truely warping a modern disc is very difficult and even massive overuse will generally cause the fluid to boil and a soft/spongy brake pedal way before the discs start to fail. The only way I've seen it down is by leaving the handbrake on after an extended track session.

This leads nicely onto the 2nd main cause of DTV - sitting at traffic lights whilst resting on the foot brake. Consider what happens when you pull off a motorway and then slow down from 70mph+ to a standstill at the lights. The brakes are really hot and pads are in contact so some transfer will occur but as the car isn't moving only to a verys specific part of the disc. Using the handbrake is better as the rears are much cooler and less likely to transfer with the very light pressure the handbrake can achieve in comparison with the power assisted foot brake.

I'm not saying this is always the cause but I've done it myself with my old VXR8. That had brakes larger and bigger than a lambos and so only needed the lightest touch to slow the car in normal day to day street driving. Yet within 2k miles the fronts were shot to hell and I'd barely got out of the running in period. After some investigation (including the discs being looked at under a microsope) I changed the way I drove it so that I used the brakes more evenly and firmer with no sitting still resting on them and they were still going strong at over 20k miles.

Interestingly in the new M3 manual it specifically mentions that "the M3 has performance sportcar brakes and should be used in the manner to which the car was designed". Kinda read that as give em a bashing rather than trying to baby them else they don't work as well as they should.

[adsgreen]

Found this - very good summary about disc vibration.
http://www.powerbrake.co.za/downloads/t ... judder.pdf

[P_G]

This has been covered plenty of times beforehand and I was one of those affected but haven't had any issues since changing pads to EBC Yellowstuff.

It isn't technically warping, usually it is pad deposition and that OEM Pagids do produce quite a lot of dust that clog the crosdrilled holes, expand and cause heat highspots on the discs which feel like juddering.

I have heard of dealerships that have replaced full front set ups only to misdiagnose that it was actually the rears.

HTH, otherwise search some of my posts on disc warping / skimming.

[Terry1948]

I would agree to the above posts. I had a problem with juddering on braking and was going to upgrade to some other discs but to get by I replaced the front pads and after about 3,000 miles the juddering has virtually disapeared. My problem I think stemmed from washing the car and letting it stand for a week or more, rust built up and being a reader of the road never braked hard.

[wolfgang]

^ In the Porsche world we were recommended to do a few emergency stops (where the conditions allow you to do so safely) after washing the car to smooth out the discs. It seemed to work too!

[neckarsulm]

^ In the Porsche world we were recommended to do a few emergency stops (where the conditions allow you to do so safely) after washing the car to smooth out the discs. It seemed to work too!

There was a lot of talk about problems with the C5 RS6 brakes (which seem very similar to ours) having the same problems and it was pad contact material. IIRC Audi Driver printed a guide on how to clean them off because it was pad material sticking to the disc and this involved some hard usage.

[adsgreen]

pad material on the discs is good - it helps stop the car better than pure friction as the material jumps between the pad and disc. It's one of the goals of bedding in new pads to get a nice even layer of pad material on the disc. The issue is that light braking can caus uneven material distribution which is a vicious circle (the more you have the more you get) and a couple of firm stops (to get heat into the brakes) followed by some really hard stops from high speed redistributes the material back evenly.

[Revolution]

There are a lot of good points above but.....

just wondering if the main dealer has put a DTi guage on the discs to check if they are warped or running out at all?

Did you bed them in properly too?

[P_G]

They usually do and in the case of Tyneside Audi will give you the readings is you ask.

Bedding in is also important with OEM Pagid pads as apparently on the Audi bedding in procedure it advises bedding in will produce corrosive gases from the pads which can damage the discs is this is not expeled during the process using the running in time suggested.