Brake issue

[jezitalia]

After the car hitting 10k KM's and a pretty grueling road trip to Switzerland pre Xmas I have noted on the last two outings that when cold, and only when cold there is a notable Vibration and wheel wobble under braking. This is present only until the car warms up.

As info the car gets a weekly outing but has amassed the majority of its Kilometerage on long runs to the UK ( From Italy where we live ) and the Swiss run. That or it does 150km motorway airport runs etc. Its not used as a run around.

Obviously I will be onto Audi service on Monday, as I hoped it was a minor issue first time.

Just wanted to sound out if any of you have had or heard of similar issues, as when I had an issue with my XKR that felt very similar it was warped discs, however that would not seem to make sense in this case as its only when cold. A quick external visual inspection of the wheels/ discs/ pads would suggest that they are not worn down.

All in all a bit baffled.

Any thoughts, advice or shared experience would be appreciated,

Cheers,
Jez

[jezitalia]

No thoughts or opinions, this forum is not normally short on them?

Car booked in at the "Stealers" tomorrow, where I will no doubt have to have my usual battle re paying for the hire car while the car is in for warranty work! Welcome to Italy once again! Will update on the problem.

[jezitalia]

For information. The car went on the diagnostic Suspension machine, all OK. Then onto the magical blue tooth connecting device, the ECU is saying no problems.

On route today there was also no shake or vibration. Strange.

One solid bit of advice was, these cars are made for driving and driving fairly hard. With that I scaled a very nice hill and found an incredible camera free road in the process.

So the car is a mystery but a great source of fun has been found in the process!

[paulcrake]

I'm using the C6 disks on a C5 RS6 and find the disks don't perform as well (including a slight vibration) if they don't regularly get given a hard time. The cross drilled holes also have a tendency to accumulate brake dust/grime. The best solution is to go out and do some hard braking and lightly engage the ABS, 4-5 times consequently from, for example 60-70mph to almost standstill.
I don't know why, but mild vibrations can/do dissapear after this procedure. Not necessarily the answer in your case, but this procedure has been discussed on the C5 forum previously and does improve brake feel.

[jezitalia]

Paul, many thanks for this.

I did notice some of the holes were caked up today when at the garage. I did suspect that with two 200km drives plus before and on salty roads some form of build up could have been to blame. Your comments completely support this theory. Thanks.

The service manager also stressed the importance of power washing the wheels to keep the Brakes crud free, especially with all the salt about.

Have hosed the wheels/ brakes and underbelly down and taken the beast for a vibe free spin.

Can't wait to hit that mountain road again soon!

Cheers,
Jez

[paulcrake]

Jez, I didn't think of the salt, but yes it does manage to find its way in there.

I would be interested if it makes a difference.
Cheers, Paul

[morginator]

I had something similar on my old C5 RS6. Had to change the discs 5 times only 2 under warranty because of shudder. Tried everything wheel balancing etc. On the 6th atempt I upgraded them with the drilled discs which worked perefectly until I proper wore them out. Audi told me it was my driving style, I am more of a poser than nutcase at driving. Now the same thing has happened on my C6 Audi state they have to do a test on the discs before I can claim under warranty.
When It happened on my C5 I was given a brake run-in protocol by Audi.
A sample is,
1.Select a suitable route for performing the routine for wearing brakes.
2. Brake the vehicle 50 times from 100kph to 20kmh
3 Always allow the brakes to cool off between decelerations by driving for 1 minute at 80k/ph
It goes on.
I am sure I saw in an Audi Magazine the Head of Audi saying this was all wrong it was all caused (vibration) by a residue forming unevenly on the discs.
I shall try and post the whole document on here
Sorry if I went on

[paulcrake]

Yes there is some document going around saying as such.
C5 RS6 has a tendency to distort disks when the axle flange/ bearing is not running true. I changed this after speaking with Grizz and so far so good... Shouldn't be happening to a C6 at this early stage in life.
Those wear-in instructions apply to new disks and re-machined disks. My experience having worn in several new sets of the C6 disks is simply sensible driving. However for the protocol to clean the disks up the brakes need a hard time and it doesn't do any harm giving the ABS a workout

[55marcuss]

My Old Man had this on his C6 when about 6 months old, the Stealers told him he had warped the discs by "not driving it enough"!
This was after he returned to the UK from a round trip to Amsterdam...
They replaced the discs and pads but refused to do so under warranty, so he paid in full - as I said , he is old!
I agree with the jet washing and hard stops remedy as it works on my C5 which also has cross drilled discs

[Nudenut]

Mine reguarly feel a bit grumbly from cold... same as, give them a couple of hard stops and all is good!!

[ecain63]

Different car completely but similar disc size etc. The front discs on the M5 started to vibrate under high speed braking. After some worry about brake reaction arms and control arms we narrowed the issues down to the discs themselves. The previous owner had obviously got the discs up to temperature one day then had to stop at traffic lights or something, leaving his foot on the brake. The discs cooled, but not in an even fashion due to the contact of the pads. As a result the discs effectivly warped and dont expand evenly when they hot and it causes a vibration. It wasnt really noticable at normal road speed but when braking hard from 80 or 90 (or even 150 on one occasion) there was definate wobble. The cure was new discs.

Hope this helps in some way, shape or form.

[Muzzlehatch]

Vibrating brakes are not usually caused by the disc warping (this in itself is an extremely rare occurrence with any discs), but deposits from the pad bonding to the disc due to overheating and/or underuse, etc. That's why a few hard stops usually cleans it up.

Oh, and I'm new here (although looked at C5s a couple of years ago). I'm starting to looking around at RS6 Avants, and can't find any "usual problems" to look for. Any pointers? A purchase could be made in the next week or two.

One thing I would ask - How different in the C6 to drive to the C5 (bearing in mind I've only driven a C5 RS6 with PSS9s)?

And is there noticeably more room for kids clobber and bikes in the back of the C6?

[grizz]

The c6 is miles apart form the c5 .. More space , comfort and 10yrs more refinement ..
The factory adjustable suspention is great ..

[morginator]

Muzzlehatch has stated very much what the Head of Audi said in a magazine about the RS6 brakes last year. I cannot find the article though.
It sounds like we keep wasting money on warped discs when really all we need to do is take the beast for a jolly good spanking.I have a C6 and had a C5 for 6 years, I love the C6 for refinement and spanking my old car in a drag race, but really miss that V8 sound