13,000 miles warped disks - yes another one....

[Revolution]

okay, glad you got sorted - who skimmed them and presume it was off the car???

[P_G]

Off the car; someone Stuart at AAS knows who does it for pin money.

[mark758]

Just an FYI on sourcing EBC Yellow...

Spoke to the nice folks at Camskill who don't have any rear Yellow in stock and felt it may take 6 weeks for them to come into stock from EBC.

Then jumped online here
http://www.ebcbrakesdirect.com/car/part ... 2005%2D%29#

Delivered by Friday for £10 less

[Dom81]

One thing that you might want to try is to see if you can re-bed the pads and discs in. Simply find a nice quiet (and safe!) bit of road and perform some firm but not hard braking stops from about 50mph to 10mph. You don't want the abs kicking in or either have the car come to a stop. The aim is to try to get some decent heat into the brake system so that they are in their peak operating zone. Do this about 5-7 times in a row and you should be able to feel the brakes reach temp as the'll be working alot better than cold. Once you're happy the brakes are working well try some very hard threshold braking from 70 (faster if on private airfield) to 10mph. Again, you don't want the ABS kicking in or come to a standstill but at the same time slow the car down as hard as you can. Do this about 3 times then go for a leisurly drive for about 10-20 minutes to cool the brakes. Try to avoid stopping or use the hand brake if you have to. I've used this one other cars that have been diagnosed with warped discs and this has removed the built up uneven pad transfer and as a nice bonus can stop squeling brakes if you have high ceramic compound pads.

That's great advice - thanks. I've read similar (and used it when bedding in my latest pads) but your summary makes a much easier read, even though it probably contains the same process

[ArthurPE]

That's great advice - thanks. I've read similar (and used it when bedding in my latest pads) but your summary makes a much easier read, even though it probably contains the same process

you mean like this?

...
sometimes the rotors get a pad depsot on them, and shudder a bit...happens to me...
I clean them as follows:
right after washing the car, the rotors will rust
I take it out and do 5 stops, 80% of full force, from 70 to 10 mph, one after another...only 10-15 seconds between
then I drive 5 minutes with no braking to cool them down, then park it
clears it right up

it's a standard procedure:
Zeckhausen has a good write-up http://www.zeckhausen.com/bedding_in_brakes.htm

another thing to remember
the discs are floating and cross-drilled, both will introduce some NVH

[P_G]

I hate to say it but that process doesn't always work in practice. It's what I tried on three separate occassions with my discs and on two it made them worse.

My theory is that the OEM Pagids are just too soft to clean up deposited discs and they ave already deposited so much they themselves are uneven.

The third time I purposely cleaned out all the cross-drilled holes and although it worked for a matter of days thereafter to vibration was back again. If the holes become clogged (why I suggested they are too small for purpose) the heat spot build up and localised disc deformation is so great that it is equivalent to a few thousand miles worth of disc wear to get them true again and more then can be done with a series of hard stops.

If you are going to do this it would be better with a brand new set of pads, Carbotecs perhaps just to clean up the discs. All said though you shouldn't really have to do this with a car. Surprising maybe that R8's, RS6's and TT-RS's now all used fixed front discs rather than floating. When on the Neckarsulm tour we couldn't get an answer why. But Autocar's TT-RS has had 'warped' discs also (Steve Sutcliffe blogged about it) and had them replaced FOC under the RS charter. I suspect if it happens again they won't be so lucky.

[adsgreen]

Have to say I can't stand cross drilled brakes.
I've never had a set that worked properly and 99% of them are actually drilled rather than forged so you are starting with a weakened disc even from new.
The best brake discs I've ever used were forged with grooves and dimples rather than holes. The dimples have all the advantages of the holes with none of the downsides - one example http://www.kinetixbrakes.co.uk/
It's certainly something I'm going to look at when the discs need changing.

As for pads, has anybody tried Carbon Lorraine pads? they've kinda created a positive storm on other forums for my other marques and are light years ahead of Pagid's (and I like those). RC5+ are stunning for the road and RC6 for track

[bye bye]

Having Googled "Steve Sutcliffe TT-RS" I found this and it concurs with my experience.

http://www.powerbrake.co.za/downloads/t ... judder.pdf

Yesterday I went out and tried what adsgreen/ArthurPE recommended. Surprisingly, I do think there is an improvement but it's not cured. Maybe if I did the same over a few days it might sort it out.


However, I do not expect to have to complete this kind of activity after just 13K miles. My RS4 is my daily driver and I need it for my job so I do not abuse it.

My last car was a Porsche 987 Boxster S. I used to drive the car so much harder than I do the RS4. I got 45K miles out of the front disks before I sold it(I did change the pads at 30K) and a prominant Porsche Independent reckoned I had another 5-10K miles left in the disk.

Still waiting to here from Audi.

Mark

[adsgreen]

Mark - I think the key bit is that you say you drove the Boxster harder than the RS4.
I was used to non servo Elises (had three) before I got my VXR8 - as such my brake pedal feel through my foot was a little... "enthusiastic" as with the Lotus it was pressure that dictated braking (generally requiring a fair bit as no servo) so getting in the heavily assisted Vauxhall resulted in lots of emergency stops 'till I adjusted... unfortunately I adjusted too much and admit to using the brakes very gingerly in day to day driving. It took less than 3k miles for my front discs to be ruined but luckily was anew car and replaced under warranty. They started going again within another 2k miles but this time I was more ready for the pre-trashed disc feedback through the pedal. After some research I found the above points about the high spot pad material transfer process with lightly used brakes and changed style. After a few brake clearing processes (I agree - takes a couple to bring the discs back but once per day is enough as don't want to overdo it!) they were fine up 'till I sold the car at 30k miles.

I'm not saying you need to be doing threshold stops every time but check to see if your driving style encourages coasting on a very light pedal or sitting at lights with the pedal down. If so, then just a slight change to make sure the entire pad is making good contact will be enough. The RS4 is much heavier than the Boxster so the heat in the system will be higher which encourages pad transfer.

[adsgreen]

Surprising maybe that R8's, RS6's and TT-RS's now all used fixed front discs rather than floating. When on the Neckarsulm tour we couldn't get an answer why. But Autocar's TT-RS has had 'warped' discs also (Steve Sutcliffe blogged about it) and had them replaced FOC under the RS charter. I suspect if it happens again they won't be so lucky.

Strange - floating discs are fitted to help prevent warping by allowing the metal to expand without distorting anything. However... much more expensive so I suspect that Audi have found a disc type/manufacturer who can give similar performance and reliability for less money.

[P_G]

The RS4 is much heavier than the Boxster so the heat in the system will be higher which encourages pad transfer.

That is the other issue with the design, with it being a pinned rather than vaned disc the air flow over the outer surface is great especially with the undertray air ducts, however the airflow through the disc is poor which I believe contributes to high spots.

I'm still hoping at some stage Willwood are going to come to my rescue and produce discs for the RS4 as they dimensions and figures have been sent to them to consider doing so. I know JHM do RS4 discs with a larger vaned central air gap but with exchnage rate and import prices they are quite pricey currently. They do have the advantage however of being lighter as well so reducing unsprung weight by about 15-20% IIRC

[ArthurPE]

adsgren: are you sure the discs are forged?
casting iron is a much better process for this application
after looking at the hardness specs, they can't be forged...they would never wear, and forged steel has a low coef of friction, they would not work well as braking material

wt doesn't have much to do with the heat...friction is a unitless quantity and the brakes are larger, so unit heat/lb or sq inch would be ~ the same...
plus the energy disappated ~ 1/2 m V^2
so linear with weight/mass, but proportional to the square of the velocity
so even a car that weighed 20% more with the same brakes would only have 20% more heat to shed...
but if it were going 20% faster almost 45% more heat...
so for equal speeds, if the car that weighed 20% more, had 20% more swept area...heat gain/unit area or mass will be equal

I installed the euro rotors on my M3 (we did not get them for the very reasons we are discussing: NVH and 'wobble', they figured too many complaints in the US market)
I got close to 75k mile/set, never had an issue, other than the standard humming and such...and they weren't worn to the limit, I changed them because of stress cracks and BMW's recomendation (another reason we didn't get them, lawsuits...'they are not worn, so don't replace them', then bam! they shatter)

the floating will help minimize vibration in another way: the disc can slide and allow radial runout which will allow the pads to stay in contact as the they ride the disc...

it's like anything...compromise, there are advantages and drawbacks...

[ArthurPE]

aren't they internally vented/vaned?
air is directed at the center, and thrown out via centrifugal action...
the M3's were actually directional, different parts for each side...

another important variable in the system is the wheel design, they can really augment cooling...remember the e34 M5 vaned discs?

here's the JHM stuff
http://www.jhmotorsports.com/shop/catal ... c05dca3df6
not sure I'd be comfortable rebuilding the rotors...
plus if you look at the second pic, they appear to have a much thinner wearing surface?
especially when you can get a set of oem for $150 more
but a lot of people do swear by the JHM stuff...

That is the other issue with the design, with it being a pinned rather than vaned disc the air flow over the outer surface is great especially with the undertray air ducts, however the airflow through the disc is poor which I believe contributes to high spots.

I'm still hoping at some stage Willwood are going to come to my rescue and produce discs for the RS4 as they dimensions and figures have been sent to them to consider doing so. I know JHM do RS4 discs with a larger vaned central air gap but with exchnage rate and import prices they are quite pricey currently. They do have the advantage however of being lighter as well so reducing unsprung weight by about 15-20% IIRC

[adsgreen]

adsgren: are you sure the discs are forged?

By forged I mean the holes are part of the orignal casting and not drilled after the disc has formed.

Even then I don't like them - dimples much better.

[P_G]

aren't they internally vented/vaned?
air is directed at the center, and thrown out via centrifugal action...
the M3's were actually directional, different parts for each side...

If you have a look at them the next time you change your discs you will notice they are not airfoil vaned, they are pinned. Airfoil vaned discs using centrifugal action draw air into the space at a greater flow rate then air forced into them and expel it quicker too.

The JHM discs do have thinner wear surfaces to accommodate the larger vaned air gap between the discs whilst retaining the OEM overall thickness as you will see from the dimensions given, you lose 5.5mm of overall thickness of OEM or 2.25mm per plate.