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      01-17-2013, 07:37 PM   #1
Swashplate
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My front rotors are warped....

So,

Braking experts it looks like my fronts are warped. So I was under the impression that these rotors did not warp or did so rarely?

Insight would be apperciated.
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      01-17-2013, 08:22 PM   #2
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Silly question, but how do you know they're warped?
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      01-17-2013, 08:34 PM   #3
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Interesting write up here: http://www.stoptech.com/technical-su...nd-other-myths
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      01-17-2013, 08:45 PM   #4
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Yes I have read that write up. Interesting read.

Well i was getting a serious medium frequency when i would come down from 90-100 to 60 in the pedal and the wheel. So I took it to a very capable BMW only shop that I like using Broadstroke Associates and their tech drove it then put it up on the lift and we discussed the issue. They are where the warped rotor issue arose.

35000 miles on the car and never seen a track day. Now that being said, no track days means nothing because I drive pretty fast.

I will mic for thickness and put a feeler on them to check flatness. I know what warped rotors feel like historically speaking but have not done brakes on this car. Well more than a flush.
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      01-17-2013, 08:51 PM   #5
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^ Yep, uneven deposits is the most likely cause. Floating rotors are unlikely to warp in particular.

Bedding procedure often cures it. If pad is deteriorating, new pads plus bedding are called for.
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      01-18-2013, 12:18 AM   #6
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Quote:
Originally Posted by Sir Digby Chicken Caesar View Post
Yes I have read that write up. Interesting read.

Well i was getting a serious medium frequency when i would come down from 90-100 to 60 in the pedal and the wheel. So I took it to a very capable BMW only shop that I like using Broadstroke Associates and their tech drove it then put it up on the lift and we discussed the issue. They are where the warped rotor issue arose.

35000 miles on the car and never seen a track day. Now that being said, no track days means nothing because I drive pretty fast.

I will mic for thickness and put a feeler on them to check flatness. I know what warped rotors feel like historically speaking but have not done brakes on this car. Well more than a flush.
You need to rotate the rotor with the wheel off, but lug bolts in place with either a spacer or nut and washer under each bolt so they can be torqued to spec, then use a dial guage to measure the runout at the edge, middle and inner part of the brake surface. If the runout is more than 0.05mm over a full rotation, then the rotors are likely warped. Also, the thickness variation at a specific radial position should not vary by more than 0.01mm around the diameter, measured with a micrometer.
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      01-18-2013, 12:09 PM   #7
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Quote:
Originally Posted by aerobod View Post
You need to rotate the rotor with the wheel off, but lug bolts in place with either a spacer or nut and washer under each bolt so they can be torqued to spec, then use a dial guage to measure the runout at the edge, middle and inner part of the brake surface. If the runout is more than 0.05mm over a full rotation, then the rotors are likely warped. Also, the thickness variation at a specific radial position should not vary by more than 0.01mm around the diameter, measured with a micrometer.
Thanks for the procedure. I am curious. I had considered running them on a CMM but it would be hard to maintain torque on the rotor unless i built some sort of jig. A bit more detective work than I am willing.
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      01-18-2013, 12:12 PM   #8
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Quote:
Originally Posted by Finnegan View Post
^ Yep, uneven deposits is the most likely cause. Floating rotors are unlikely to warp in particular.

Bedding procedure often cures it. If pad is deteriorating, new pads plus bedding are called for.
Yea I tried that but to no avail. The conclusion we have made is there were uneven deposits that created a hotspot. I have heard frequently that our rotors dont warp but I think thats a load of codswallop.
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      01-18-2013, 08:31 PM   #9
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I don't think they are warped. With heavy track use, I have never heard of a warped rotor, even with racing pads. Crack.......yes.......from over heating, but not warped.

Find a different shop.

Listen to Fin
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      01-18-2013, 09:25 PM   #10
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I guess it could have created a hot spot due to uneven deposits, but on a street car I can't see the temps getting that hot due to an uneven pad deposit. I suppose a hard spot could develop from repeated overheating in that one spot, but I'm skeptical. It may just be hard to remove the uneven deposits completely.

One possible solution would be to run a set of "scrubber" pads to remove the deposits. I think I have a box at home--I'll check--could part with them cheap if I do. Cheaper than a set of rotors if they're still well within spec and do not have a run out issue.
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      01-20-2013, 03:47 PM   #11
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I do have a set of the scrubber pads.
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      01-20-2013, 09:08 PM   #12
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Quote:
Originally Posted by seank View Post
I don't think they are warped. With heavy track use, I have never heard of a warped rotor, even with racing pads. Crack.......yes.......from over heating, but not warped.

Find a different shop.

Listen to Fin
^This!
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      01-22-2013, 10:45 AM   #13
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Wouldn't it be easier to just take the rotors off and have them turned? I know that near me, my local O'Reilly's turns rotors for like $8/each. I had a set of rotors that were glazed over real bad from cheap pads, and they were able to turn the rotors without taking hardly any material out of the rotors.

Seems like that would be easier than using "scrubber pads", and probably cheaper?
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      01-22-2013, 10:47 AM   #14
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You can't turn these rotors.
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      01-22-2013, 10:54 AM   #15
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Is there any other reason the rotors can't be turned other than they're drilled?
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      01-22-2013, 06:03 PM   #16
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You actually can turn drilled rotors its just time consuming and nobody likes doing it. So they say you cant. My rear rotors were warped when I was still under warranty so BMW replaced them. The make an awful roar during high speed braking.
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      01-22-2013, 06:35 PM   #17
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Anything BMW says I take with a grain of salt now.

They told me my rotors were warped, brakes making loud noises and needed replaced. When I know for a fact they weren't.

I was running HP+ pads and they obviously don't know what an aggressive bite feels like (or sounds like...lol). Drove the car after I picked it up and it was the same as I dropped it off.


Shaving rotors just compromises the rotor itself, and is a waste of time and money. If your rotors are actually warped, then something else is causing the problem....not just the rotor.
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      01-22-2013, 08:10 PM   #18
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Quote:
Originally Posted by Finnegan View Post
Bedding procedure[/url] often cures it. If pad is deteriorating, new pads plus bedding are called for.
Quote:
Originally Posted by Sir Digby Chicken Caesar View Post
Yea I tried that but to no avail. The conclusion we have made is there were uneven deposits that created a hotspot. I have heard frequently that our rotors dont warp but I think thats a load of codswallop.
I had a wicked vibration following a track weekend early in my HPDE carreer when still on OEM pads. The vibration stayed with me for 5 months of weekend driving on the street, plus 3 20-minute track sessions at VIR before things got hot enough to remove the deposits. They can be stubbon--consider bedding again, and very aggressively, before you throw money and time at the problem.
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      01-22-2013, 09:16 PM   #19
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Ok, fine you win. I will try bedding them in again. I really do appreciate all of the input.


They actually feel like they are getting better, but that might also be me being careful in the slippery weather.

I still won't buy that you cant warp these. I used to be an Aerospace QA Manager for a company that made machined parts for Boeing. You apply heat to metal it is going to change shape. Now not like in the way I have seen where you hog out a 4ft x 3in piece to an average thickness of .20....shall we say lets do the twist....

But I am also willing to hear good arguments and listen to folk that have experiance and knowledge. Hence why I even made a post. I respect highly the opinion of most on here. This is a very special forum. Special for BMW and even more special for performance cars. Don't beleive me go to NASIOC (Subaru)....I used to have an STi and there was so much BS and willy measuring.

I love you guys and this hobby. Ok, enough of that. Must be the Hendricks...

When I am back home I will see if I can get this bastards sorted.

Thank you again for your time and insight.
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      01-23-2013, 12:40 AM   #20
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Quote:
Originally Posted by elwesso View Post
Is there any other reason the rotors can't be turned other than they're drilled?
They are floating rotors, the aluminium hat is joined to the cast iron brake surface by stainless steel pins. You can't machine the brake surface accurately by clamping the hat, as it will just move on the pins.
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      02-09-2013, 10:03 PM   #21
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Ok, so looks like they were out of spec anyway. They had a mighty lip on them. I guess I have two heavy feet.....

I also did H&R springs and the CDV delete at the same time. Oh my god why didn't I do the delete before. What a difference! I didn't use the 15mm pad on the rear like some of you have. I will see how it looks once it has settled a bit. But it looks fine right now.
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