Warped rotors in relatively new Audi A8
03-21-2017, 08:14 AM
#11
AudiWorld Super User
... Minor pulsating should mean minor warpage and sometimes the rotors are not warped at all. It's pad deposits on the surface the rotor. Hard for me to believe our rotors cannot be turned at least once. Especially when done properly. It's a very small amount of rotor that is shaved if you have it done when it first starts. I'm prone to think the business of selling new rotors is the main driving factor of shops / dealers.
Agreed it can be pad deposits. Those can sometimes be dealt with the old fashioned way--sandpaper to rough up.
Rotor is mounted on pins like a quasi two piece. Apply side pressure to it and the rotor surface can move on the pins even though center rotor hat is clamped in the surfacing machine. Folks seem to keep wishing it were different, but the answer remains same. See picture below from A8 into SSP. 17" refers to minimum wheel size BTW, not rotor diameter. Best hope for the D4 owners with the 380mm size is an aftermarket option opens up for higher volume SQ5. Audi borrowed from the D4 parts bin for the SQ5 set up.
Last edited by MP4.2+6.0; 03-21-2017 at 08:18 AM.
03-21-2017, 08:18 AM
#12
AudiWorld Senior Member
MP, is this also the case for the OEM front 356mm? I thought I had the 380 but I called a dealer and via my vin they said I have the 356 front.
Last edited by LexusLSguy; 03-21-2017 at 08:22 AM.
03-21-2017, 08:26 AM
#13
AudiWorld Super User
I don't know, though I thought the 356 mm was maybe a spec misprint. The ones I know of are:
- 365mm R8+RS5 size
- 380mm size that seems to be all the U.S. 4.2's and the 3.0T? (and maybe 4.0T in D4 application, plus SQ5); later R8 380mm may be this too
- 400mm size for 4.0T for S8, S7, S6.
- also used in BMW's starting with last gen M6 (and then M5), but wheel bolt up pattern is different for starters so no cross over like you can find occasionally with Merc stuff.
I had "conventional" rotors at 385mm on the D3 W12. They weighed 39 pounds, which was getting ridiculous. The unsprung weight screws with ride and probably was/is a further contributor to the upper control arm issues the D bodies are known for.
To answer what size you have as a practical matter, just go eyeball it w/ a tape measure in hand. 356 to 380 is 24mm or almost exactly an inch, so you should be able to deduce if it is one size or other even with wheel on, give or take a bit of error. Sizes and wear spec/minimum are also laser engraved on rotor. Sometimes in hat area, sometimes around rotor edge. Wheel has to come off for that, and wire brush used to clean rotor edge to find the markings.
Last edited by MP4.2+6.0; 03-21-2017 at 08:35 AM.
03-21-2017, 08:35 AM
#14
AudiWorld Senior Member
Audi Parts shows the 356 as an option for the front. I will have to confirm again. I edited my post after you quoted but a local dealer quoted me as having the 356 fronts. I'm would think the design is the same on the fronts vs the rears for the various sizes.
Link
Link
03-21-2017, 08:37 AM
#15
AudiWorld Super User
Audi parts shows the 356 as an option for the front. I will have to confirm again. I edited my post after you quoted but a local dealer quoted me as having the 356 fronts.
Link
Link
Yes I know, but don't trust Audi listing as Gospel. Can sometimes be a non-U.S. motor not offered here that gets jumbled in the slides they forget to adjust for. Audi sizes brakes for motor torque, vehicle speed and weight, per probably Euro requirements. I likewise edited my post for practicals of...just go eyeball it with a tape measure. Then you will have real world answer.
03-21-2017, 09:08 AM
#16
AudiWorld Member
I personally would rather turn them for about $40 - $60 vs buying a new set between around $700. It's not like the rotor performs any better vs a new one. As long as its in spec. Ideally, I want to spend the least amount of money on things like this and use it for other purposes. Getting at least 60k - 80k miles out of a set is not too much to ask for, imo. The front rotors also may not fit on the machines because of their design.
03-21-2017, 09:15 AM
#17
AudiWorld Senior Member
03-21-2017, 09:32 AM
#18
AudiWorld Member
I'm aware of your devotion to your prior ride and I mean nothing personal but I'll take the Audi, warped rotors and all. Just couldn't ever warm up to the Lexus. Kinda lifeless you me. Hope your experience with the A8 is as awesome as the 430
03-21-2017, 09:51 AM
#19
AudiWorld Senior Member
I like the Audi a lot otherwise I would have purchased the 460. I know the cost of maintenance will be higher but some stuff is just kind of stupid. Like the front rotors. This is also my first German vehicle so maybe there is some coming to term with things.
Last edited by LexusLSguy; 03-21-2017 at 09:55 AM.
03-21-2017, 10:17 AM
#20
AudiWorld Member
Not as reliable as the Lexus (nothing is) but not terrible. IMO, much more enjoyable to drive however. It is German after all.
Fortunately you get to compare, not a bad deal
Enjoy
Fortunately you get to compare, not a bad deal
Enjoy