rscultho

There are several threads that have some information around the front brake rotors on the A8/S8 380MM/400MM front brake rotors...but I haven't found any detailed technical discussion on why these rotors are so expensive, and why they aren't produced by any aftermarket suppliers/retailers.

My car has a smidge over 35K miles and the front rotors are severely warped. Many seem to have this issue.

Does anyone have any technical data on these rotors? Do they have any special metallic compounds in their manufacture? Are they steel or iron?

Just don'y understand why these rotors are so expensive, and why they can only be sourced from the dealer. There are enough of these cars on the road that aftermarket suppliers could make significant profit if they offered an alternative to dealer sourcing.

TIA

LexusLSguy

It's the design of the rotor which is why there is no aftermarket on the front. I'm sure this was done on purpose. Anyway, your best bet searching online and asking the parts guy to match. This should not be an issue. As far rotor size, the bigger the better when it comes to stopping power. Also means more $. I would go softer pads vs OEM. With the right combo the pads will take like 85% of the wear vs the rotors and "warpage" due to pad deposits. In other words, getting 2 - 3 sets of pads per rotor change.

MP4.2+6.0

Welcome to patents. Sole source supply from obscure Euro manufacturer to Audi. Rights apparently co owned by them, Audi and BMW (similar ones also used on some performance BMW's). Quasi two piece design with alloy center hat attached by permanent pins to lighten pig weight you get with cast irons as they get this big. Layman's version of the techno stuff. Thus as a counterpoint, the 385's on my D3 W12 in the conventional cast iron design weighed 39 lbs new, each. All unsprung weight that deteriorates ride, suspension longevity, fuel economy and acceleration at margin. The last two are marginal but part of equation. And yes, if you could find conventional cast iron alternatives, those would be results. If this were commodity Toyota, Honda or GM they would spring up. On one off Audi, unlikely. Best hope actually is 380mm is also used on SQ5. As those age, might be a bigger aftermarket than for A8 boutique case.

Meantime, (rather than suggest your rotors may not be warped...) tell us why you think the rotors are actually warped. Have you had them--and your suspension--checked out by a shop? In other words, anything more than you think you feel vibration when braking?

rscultho

I appreciate the information. I really did not start the thread to discuss my problem, but I understand how suspension and braking systems work in conjunction with tire functionality and performance. I did talk my dealer into checking my braking system out(without charge) which will occur in a few days.

Of course brakes and associated components are wear items, and do have to be replaced. They have (at least) admitted that there is a known problem with the rotors which I found out when I called, so maybe they are *actually* acknowledging and issue? I will find out...

MP4.2+6.0

FWIW, watch for two non-warped rotor issues:
These are not known as long life rotors either--not unique to Audis by any means these days among the raft of Euro rides. It is also a function of how much wear they permit on rotors, especially in front. Desire for lower weight offsets that. Real cost of ownership question I think on D4 rotors is whether you can get a second set of pad life out of them these days. Some owners report not, but hard to sort dealer sales aggressiveness there. But three pad sets on a modern Audi is a pipe dream if changed only after 80-90% of wear life. If dealer goes there (on your nickel), be sure they give you the actual pad and rotor measurements. Dealers have a strong interest in talking you into expensive brake jobs for "safety" while being vague on actual wear situation. Some try to say that if rotor wear will drop below spec by next expected pad change, they should be changed now. To me that is sales baloney and a distortion of what the wear spec's use really is.

rscultho

Dealer saw the car, and has admitted that these rotors have been a problem. Also, they discovered problems with the front calipers sticking...they're replacing everything under warranty.

Service rep agreed that with pads at 8mm, there is no reason for the rotors to be warped at 35K miles.

However, they did say that Audi recommends replacing pads at 5mm, but wear sensor does not indicate replacement until 2mm. I asked why wear sensor went that low when recommendation was at 5mm...they said they did not know.

Wow - they were honest about the rotors...I was shocked.

rscultho

Further update: Turns out my calipers were fine. The rotors were so warped that they were wobbling against the pads and each side had one pad that was worn down almost twice the other one.

The dealer replaced everything under warranty.

I asked and was told the new rotors were not supposed to warp like the ones removed.

Time will tell...

Burfy

Hello guys, found this interesting thread on front brake disc problems on A8 D4. I keep having issues with the front brakes on my A8 causing serious brake judder. I've had new discs and pads all round. And the judder comes back again within a couple weeks. The garage have identified it is the passenger side front which is causing the judder at the moment. How can this be rectified? Its a 2010 A8 D4 4.2 TDI.
When cruising on a motorway I can feel the car pulsing as if a brake is being applied momentary, could this be a mechanical issue or could it be an electronic issue - i.e the self drying brake system malfunctioning??

I'm hoping to get this sorted as its very irritating.

MP4.2+6.0

As far as I know, the auto wipe function is only for carbon ceramic brakes, unless someone (seriously) played with VCDS to enable the function on your car.

Various:

1. Look the caliper function where it slides across what are probably very large metal pins. There will be some kind of rubber or plastic bushings in there, which can wear. I know they are in D3's, and were available as an (obscure) piece part.
2. Possible bad wheel bearing starting to allow hub run out. You don't say miles/km on car, but 2010 is a very early Euro D4.
3. While it would't normally tie to a brake sort of feel like you describe, perhaps the usual wear suspects in suspension. Especially for an early one, your sway bar links are probably long since toast if not already done. Sloppiness could lead to vibration on braking. Those are easy to replace. Perhaps upper control arm bushings (another wear area for D3's and 4's), though would be even harder to tie that to the pulsing feel that you think may be related to or feel like brakes.

Burfy