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Discussion Starter · #1 ·
I had my brake disks replaced by a main dealer back in March 2010 as they were badly corroded and juddering.

The brake judder came back gradually over the last couple of months so I booked the car in again to have them checked at the same time that the MOT was done. I was expecting that the thrust arm bushes were probably shot, but apparently not, the front disks are warped say the dealer. As they were only replaced 8 months ago and are hardly worn at all, the dealer asked BMW for a warranty replacement which has been approved.

Now comes the but ....

My OEM wheels have been refurbished do to the lacquer peeling from the inside, actually about 2 years ago, how many original wheels have not been refurbished by now? When refurbished the entire inside of the wheel was painted black, as I've seen done many, many times.

Now, apparently, BMW are saying that the inside surface of the wheel that comes into contact with the brake hub should NOT be painted and must be bare metal. To be fair, original OEM finish wheels that I have seen (never seen a original finish style 65 M5 wheel, but E39 style 66 and E46 style 72, 73 and 135 wheels) have been bare metal on this surface. They are saying that unless the inner contact surface of the wheel is stripped back to bare metal, further warranty claims for warped disks will not be approved.

So, first, what does anyone think of this? Is it likely that the extra heat dissipation by conduction direct to the wheel metal from the hub would prevent disk warping? I've always though that warped disks were just an excuse used to get you to replace your disks early and in practice hardly ever happen!

Second, for people who have refurbished OEM wheels, is the inner contact surface painted or bare metal? If it's painted, has anyone had problems with warped disks?
 

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Wow, that's a first....paint on the backside of the wheel can cause rotor warp. Crazy stuff.
But it would be a piece of cake to remove that portion of the paint using a simple wire wheel brush attached to a handheld drill.
 

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So, first, what does anyone think of this? Is it likely that the extra heat dissipation by conduction direct to the wheel metal from the hub would prevent disk warping? I've always though that warped disks were just an excuse used to get you to replace your disks early and in practice hardly ever happen!
In my experience it's pretty tough to actually warp a brake rotor (although, you can do anything if you try hard enough :wroom:). Uneven brake pad deposits are much more likely. I've heard that over-torqued wheel bolts or running through standing water with very hot rotors could cause warping, but I don't have any experience with that to say if it's true.

I see you're in the UK - are your front discs the Euro floating design? I recall reading something a while back about the "Euro" design and rotor warping complaints, but I don't remember any details. Did the dealer measure the runout of the rotors to determine if they're warped or some other method? I ask because sometimes out of balance wheels or suspension problems can cause vibration/juttering when stopping.

I don't see the paint affecting heat transfer enough to cause warping. But, if it was uneven, that could cause vibration. Do you feel the pedal pulsating when you hit the brakes? Is the vibration only present when using the brakes?

Glad you're getting free replacements.
 

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Discussion Starter · #4 ·
I see you're in the UK - are your front discs the Euro floating design? I recall reading something a while back about the "Euro" design and rotor warping complaints, but I don't remember any details.
Yes, they are Euro floating rotors.

Did the dealer measure the runout of the rotors to determine if they're warped or some other method?
I don't know yet, I'll ask when I collect the car.

I ask because sometimes out of balance wheels or suspension problems can cause vibration/juttering when stopping.

I don't see the paint affecting heat transfer enough to cause warping. But, if it was uneven, that could cause vibration. Do you feel the pedal pulsating when you hit the brakes? Is the vibration only present when using the brakes?
The vibration is/was through the steering wheel, and could also be felt as a vibration through the whole car.

Glad you're getting free replacements.
Me too, anther £700 odd would not be appreciated right now!
 

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LOL, £700? The cost of the discs is half that (and that is 3 times higher than it should be) and it takes 30 minutes to fit them. BMW are a joke.

Oh and the discs will not be warped, its just pad deposits from the awful pads but BMW monkeys won't realise that. I thought I had cleared mine but they still vibrate. I'll put the yellowstuff pads on at the weekend which are hard enough to clear the deposits.

The painted wheel surfaces will make no difference at all to the brakes but will cause tiny imbalances in the wheel rotation which you may or may not feel. I've had wheel vibration before (at over 150mph) that was cured just by cleaning off the mating surfaces of the wheel and the hub.
 

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Discussion Starter · #6 ·
£700 may be a bit on the high side to be fair, I just halved what it cost to have all 4 disks and pads, but I agree they are well over priced.

Do you get any noise at all from the YellowStuff pads?
 

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Nope but I grease them up properley. I heard some have noise from theirs. I bought them on ebay for (front and rear) £145 and they have lasted well. As I wasn't tracking the car again for ages I switched back to BMW treacle brake pads but looks like I'll be going back again.

Its £330 for two M5 front discs. The rears are cheaper.
 

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Richard,

Just out of curiosity as I'm quite near you, which dealer are you getting this diagnosis from?

I also have refurbished wheels which are black on the inside faces but I have no issues at all with vibration, the only difference is that I don't have standard BMW discs and pads but I can't really see that this would have any influence at all on disc "warping".

Mike
 

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I don't know if you can warp floating rotors from heat cycling them. Maybe if you stop in a puddle. The vibration is created somehow else, not from the paint IMHO.

This didn't warp my floating rotors, drove them for another 30,000 miles after this ordeal, just swapped the pads.
The whole idea of floating rotors is that it contains the heat within the rotor itself and does not transfer to the hub, which causes conventional rotor warping. This was the ultimate test of it.
I also did a full stop with glowing rotors, many times over.. which is not recommended, since the brake caliper heats up the space it covers on the rotor more than the rest of the rotor, causing expansion and contraction differences because of heat, possibly causing it to warp. But i had ZERO warp or issues. Replaced the rotors because they were just too shaved, with ZERO warp.

 

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I have managed to warp Euro floating rotors at the track- my fault though, the club wasn't allowing a cool down lap and I didn't spend anywhere near long enough cooling them down in the paddock. Lesson learned.

If you can actually warp them on the road (road driving tends to involved at least short straight stretches between hard braking corners) then you have a deft skill.
 

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I have managed to warp Euro floating rotors at the track- my fault though, the club wasn't allowing a cool down lap and I didn't spend anywhere near long enough cooling them down in the paddock.

If you can actually warp them on the road (road driving tends to involved at least short straight stretches between hard braking corners) then you have a deft skill.
They would have been pad deposits. You need hard pads to scrape the deposits off as some pads just build up more deposits on the deposits.
 

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They would have been pad deposits. You need hard pads to scrape the deposits off as some pads just build up more deposits on the deposits.
lol I was using Pagid yellows- hard enough? Believe me, the discs were thermally warped. I took the car out again on the same day to replicate it- the vibration did not come back (even braking from 120 miles per hour) until I had done a lap and the discs had become hot again. Terminally warped front discs.

Took it down a mountain road a week later, managed to induce some vibration and this was after 7 days of road use on Pagid Yellows. If anything was going to scrub pad deposits off it's a pad like that not going past its abrasive stage at street temperatures.
 

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Possibly not. I had discs that I couldn't bring back until I used PFC-01's on them, about the hardest pad I could find (and the most expensive). Once I had them on the discs were OK again (even when braking from 150mph) and the pads certainly didn't flatten them out, just cleared the deposits.

Whilst track work can get discs hot, to actually cause warping of the metal is extremely difficult and in every case I've ever come across its because the pad as atomised and melted onto the disc.
 

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1. Demand that your dealer put this in writing on their letterhead. And sign it. Then put a cover letter on it and have BMWAG review and confirm.

2. Ask to see a brand new OE BMW wheel. it will have the black base powdercoat.

3. Morons.

4. Did they actually measure the run out on the disc to decide it was warped?

5. See #3.
 

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Possibly not. I had discs that I couldn't bring back until I used PFC-01's on them, about the hardest pad I could find (and the most expensive). Once I had them on the discs were OK again (even when braking from 150mph) and the pads certainly didn't flatten them out, just cleared the deposits.

Whilst track work can get discs hot, to actually cause warping of the metal is extremely difficult and in every case I've ever come across its because the pad as atomised and melted onto the disc.
Warping was confirmed by Porsche 997 Carrera Cup Car mechanic/specialist having measured the run out.
 

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Discussion Starter · #19 ·
So, based on what I can find out, I believe the following statements to be true :

- Use of floating rotors minimises the risk of warping as the disks can move slightly relative to the hub allowing for expansion/contraction as the disk heats/cools, also there is less heat transfer to the hub with a floating disk design. Although warping of a floating rotor design is not impossible, it is extremely unlikely with road use.

- Use of poor quality pad friction materials results in transfer of the pad material to the disk, this can actually increase the measured thickness of the disk in places as once transfer occurs it tends to continue to build up in the same place, this can be mistaken for disk warping.

Are the above correct?
 

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Pretty much sums it up Richard.

Warping of discs is the term used simply because its common, i use the term myself even though i know its pad deposits. A bit like people who say "rocker cover gasket" when pretty much all engines haven't used rockers for donkeys years.

Painting the alloy wheel will have no ill efeects whatsoever, thats complete BS. Even if the OE wheel was bare metal (which it isn't) how do you explain everyone running aftermarket or refurbed alloys that are doing so with no ill effects regarding rotor "warp".

Coincidence for everyone else?? Laughable
 
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