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      03-22-2017, 08:49 AM   #23
crabu2
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Have you thought about getting a dial caliper and checking the thickness of the rotor and pads yourself to make sure both are good?
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      03-22-2017, 08:49 AM   #24
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Quote:
Originally Posted by moldcad View Post
No, the pads are OK and original. Besides, I used the car for 2 years w/o such a thing ever happening to my rotors

P.
My rotors look like that after every time I wash my car. Pretty normal if you ask me! But it does look like you have an issue with your pad biting the entire rotor.

My exhaust tips did the same exact thing as well. I just used some high temp spray paint (spray the paint onto a piece of card board and brush it on with a foam brush). Worked like a charm.
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      03-30-2017, 06:21 AM   #25
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OK guys, so to update you: I did just over 1,000km and both rear rotors still haven't been cleaned! Of course they do not look as ugly as in the pic in my OP - but still, there is a very distinct boarder between the inner part (which is basically clean as for normally used brakes, and looks like the front rotors which have both been cleaned and polished over their entire surface by the pads) - and the outer "band" which is still looking differently...

Can't comprehend how this is happening given the pads are planar (so said the dealer who has inspected them, and so they must be - otherwise the front rotors wouldn't have gotten cleaned, either). Any possible explanation?

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      03-30-2017, 12:29 PM   #26
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Under normal use the brake discs/rotors will last about 100,000 km and will have worn less than 1mm each side. 1,000km of normal use will remove about 0.01mm of rotor (about one tenth the thickness of a sheet of paper), so if the pitting from the rust is deeper than that, it won't have worn off yet.

Although the procedure is at your own risk, a good brake bedding should remove a few hundredths of a mm of rotor. Personally I brake from 110 to 10 km/h as many times as it takes in quick succession for the brakes to just start to fade (brake smell and pedal just starts to get soft), as previously mentioned, drive around to cool the brakes after such a session (at least 15 mins of highway driving) without allowing the car to come to a complete stop.

It likely rusted and pitted originally just in the outer band due to salty water just on that band when the car was parked. The reason the corrosive mixture is only on the outer band is due to the previously mentioned effect from the spreader spring in the caliper that pushes the outer edges of the pads apart, causing them to drag more on the inner part of the rotor than the outer edge when the brakes are not applied.

Last edited by aerobod; 03-30-2017 at 12:49 PM..
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      03-30-2017, 11:57 PM   #27
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Thanks aerobod - your explanation makes sense to me, at last! The clue being that the uneven cleaning doesn't actually occur while applying (moderate) braking, but with constant dragging of pads against the inner rotor's area...

Will do the bedding procedure, but - since it involves some "smearing in" between the rotor and pad materials - I'll only do it after my rotors are (almost) free from any remnants of iron oxide

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      04-10-2017, 12:44 PM   #28
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DIY for painting calipers?

Quote:
Originally Posted by Rayscott View Post
I have black tips and clean and polish them regularly. They look new, no soot. I painted my calipers black. Rust goes away on rotors. A little TLC and your problems are solved.
Hi Rayscott. Can you point me to a thread (if one exists) or to an external DIY resource for repainting my brake calipers? Trying to decide if this is worth doing. Mine (a 2011 E93) look horrible -- but I'm reluctant to drop a ton of money on new ones. Any suggestions would be appreciated.
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      04-11-2017, 10:01 AM   #29
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Quote:
Originally Posted by moldcad View Post
Thanks aerobod - your explanation makes sense to me, at last! The clue being that the uneven cleaning doesn't actually occur while applying (moderate) braking, but with constant dragging of pads against the inner rotor's area...
Well - I was writing the above full of hope that what's happened is more or less normal, and my rotors would shine again after some driving. Unfortunately, after some 1,500 km of normal driving (and braking, of course), the rear rotors look as per the attached picture (I deliberately re-posted the picture from my OP in this thread so that there comparing is easier). The front ones are OK, though - can anyone figure why? The only explanation that I can think of is that with LSD, my rear brakes aren't engaged fully very often while the front ones are working much harder... But I'm certainly quite concerned; please advise what I should do now....

Piotr
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      04-11-2017, 10:57 AM   #30
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Quote:
Originally Posted by moldcad View Post
Well - I was writing the above full of hope that what's happened is more or less normal, and my rotors would shine again after some driving. Unfortunately, after some 1,500 km of normal driving (and braking, of course), the rear rotors look as per the attached picture (I deliberately re-posted the picture from my OP in this thread so that there comparing is easier). The front ones are OK, though - can anyone figure why? The only explanation that I can think of is that with LSD, my rear brakes aren't engaged fully very often while the front ones are working much harder... But I'm certainly quite concerned; please advise what I should do now....

Piotr

do you know how to change pads and have the tools? because at this point I would lift one side of the rear, remove wheel, remove pads and inspect them for even surface along the entire pad length, maybe even remove caliper and clean the pins and slides and reassemble everything, then do the same on the other side. And I'd clean the rust off the disc with soap and water and a brake pad as a abrasive.
I'd also inspect the inner side of the disc to see it looks the same -
not sure if inner visible when mounted.
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      04-12-2017, 12:32 AM   #31
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Quote:
Originally Posted by moldcad View Post
Well - I was writing the above full of hope that what's happened is more or less normal, and my rotors would shine again after some driving. Unfortunately, after some 1,500 km of normal driving (and braking, of course), the rear rotors look as per the attached picture (I deliberately re-posted the picture from my OP in this thread so that there comparing is easier). The front ones are OK, though - can anyone figure why? The only explanation that I can think of is that with LSD, my rear brakes aren't engaged fully very often while the front ones are working much harder... But I'm certainly quite concerned; please advise what I should do now....

Piotr
The pads are gradually cleaning off the rotor, you can see in the lower photo that the corrosion pitting is quite deep on the outside edge from the original corrosion "event", still needs to be worn down more. Have you tried aggressive bedding of the pads, as described by a couple of us earlier in the thread?
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      04-12-2017, 12:37 AM   #32
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Quote:
Originally Posted by moldcad View Post
iDrive says still good for 60 kkm...
Eyesight (i-sight) says, not good for 60 km.

Sorry, couldn't resist.
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      04-12-2017, 12:40 AM   #33
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Quote:
Originally Posted by aerobod View Post
The pads are gradually cleaning off the rotor, you can see in the lower photo that the corrosion pitting is quite deep on the outside edge from the original corrosion "event", still needs to be worn down more. Have you tried aggressive bedding of the pads, as described by a couple of us earlier in the thread?
Yes, I can see all that - what beats me though is the fact that - although rotors corroding when car is unused and stored in a wet environment for several days is a normal thing - usually all that corrosion is removed from rotors by the pads during the first couple of kilometers of normal driving. How what you call "the original corrosion event" differed from usual - I've no idea... This happened to me for the first time ever during the 46 years of driving so many different cars!

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Last edited by moldcad; 04-14-2017 at 02:20 AM..
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      04-13-2017, 01:32 AM   #34
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It is definitely unusual, but from the fairly aggressive pitting could be caused by a chemical that is somewhat acidic or alkaline, perhaps a new type of road de-icing chemical that has been used in your area?
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      04-13-2017, 10:33 PM   #35
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Quote:
Originally Posted by aerobod View Post
Have you tried aggressive bedding of the pads, as described by a couple of us earlier in the thread?
No I did not - the pads need a clean rotor surface to lay down an even transfer film. Doing it with so much rust and pitting on the rotors could only worsen the situation.

Quote:
Originally Posted by aerobod View Post
It is definitely unusual, but from the fairly aggressive pitting could be caused by a chemical that is somewhat acidic or alkaline, perhaps a new type of road de-icing chemical that has been used in your area?
No, this is not the case. My other vehicle (Golf R) is absolutely fine; also watching other cars in my neighborhood I didn't spot a single one with the same problem. Last but not least, I'd have excessive rusting elsewhere on the car which I don't.

Piotr
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