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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > burn marks on rotors



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      04-24-2009, 10:25 PM   #1
Sparkling G
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Unhappy burn marks on rotors

Went out did few WOT's with the new map, after a few hard brakes (over 90mph down to 30mph), when the rotors getting hotter and hotter, my steering wheel will start vibrate badly when I applied medium pressure on the brakes. Parked the car and I realized there are some burn marks on both front rotors. I circle them on below pictures. Is this normal or my rotors are finished and need to be replace them. These rotos been on the track for 3 times only and have about 10,000 miles on them. If not the rotors, what could caused the vibration?
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      04-24-2009, 10:36 PM   #2
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Looks like it got really hot on those spots...possibly glazed.
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      04-24-2009, 11:50 PM   #3
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thats normal

that vibration is deposits of brake pad left on your rotors from the pads. continue to drive on them to remove them --- only w/the pad that you left them with.

i would suggest you don't apply the e-brake after hard runs where ur rotors heat up.

do you know what color metal that has titanium allow in it becomes when it is heated up and cooled? i think u can take a guess
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      04-25-2009, 12:21 AM   #4
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You should probably run a full pad bedding procedure or two to reset your rotors. They aren't "warped", they just have uneven pad material deposits which cause the pulsating.
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      04-25-2009, 12:29 AM   #5
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Quote:
Originally Posted by scollins View Post
You should probably run a full pad bedding procedure or two to reset your rotors. They aren't "warped", they just have uneven pad material deposits which cause the pulsating.
+1 listen to Scott (not me, the other Scott. No wait, listen to me, too...)
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      04-25-2009, 12:42 AM   #6
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Quote:
Originally Posted by scollins View Post
You should probably run a full pad bedding procedure or two to reset your rotors. They aren't "warped", they just have uneven pad material deposits which cause the pulsating.
how do you run a full pad bedding procedure?
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      04-25-2009, 02:18 AM   #7
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You should look up the specific procedures for your pads. but here is an example:

http://www.zeckhausen.com/bedding_in_brakes.htm

I'll sometime get the pulsating brakes problem (deposits) after a hard track session. I re-bed the pads in afterwards and I get the smooth braking back.
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      04-25-2009, 11:42 AM   #8
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but when I drive under normal condition, city and hwy speed with normal brake pressure, I didn't feel any vibrations. Only after few hard brakes (no ABS kicked in and not to complete stops) than I felt vibration under soft medium brake. I assume that my few hard brakes almost same procedure as bedding the brake which I just found out (thanks Mtek for the link)....so that why I don't why I still getting vibration.
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      04-25-2009, 11:49 AM   #9
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Quote:
Originally Posted by Sparkling G View Post
but when I drive under normal condition, city and hwy speed with normal brake pressure, I didn't feel any vibrations. Only after few hard brakes (no ABS kicked in and not to complete stops) than I felt vibration under soft medium brake. I assume that my few hard brakes almost same procedure as bedding the brake which I just found out (thanks Mtek for the link)....so that why I don't why I still getting vibration.
Thats because the rotors and pads heat up. Increases the runout and bonding between the pad and material on the rotor.
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      04-25-2009, 12:00 PM   #10
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Quote:
Originally Posted by O-cha View Post
Thats because the rotors and pads heat up. Increases the runout and bonding between the pad and material on the rotor.
it didn't feel safe...it was not small vibration...the whole car felt the vibration too!! do I need to have my rotor machine and re bed them?
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      04-25-2009, 12:05 PM   #11
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Quote:
Originally Posted by Sparkling G View Post
but when I drive under normal condition, city and hwy speed with normal brake pressure, I didn't feel any vibrations. Only after few hard brakes (no ABS kicked in and not to complete stops) than I felt vibration under soft medium brake. I assume that my few hard brakes almost same procedure as bedding the brake which I just found out (thanks Mtek for the link)....so that why I don't why I still getting vibration.
The process is really dependent on getting the pads/rotors up to the transfer temperature to evenly coat the rotors (that's why the procedures may be different for different pad types). I've had to do the procedure twice in some cases to get even transfer to occur. You should end up with a distinct blue sheen on your rotors after the process. This is fine and will go way in a few days. This is a sign that you got the brakes up to proper temp.

Not getting them hot enough will cause uneven transfer = vibration.

You can also have the rotors re-finished which could help start over. You bed in brakes because it really improves braking performance.
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      04-25-2009, 12:14 PM   #12
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"After the break-in cycle, there should be a slight blue tint and a light gray film on the rotor face. The blue tint tells you the rotor has reached break-in temperature and the gray film is pad material starting to transfer onto the rotor face. This is what you are looking for."

"After the first break in cycle shown above, the brakes may still not be fully broken in. A second bed-in cycle, AFTER the brakes have cooled down fully from the first cycle, may be necessary before the brakes really start to perform well. "
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      04-25-2009, 12:44 PM   #13
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Quote:
Originally Posted by MteK View Post
"After the break-in cycle, there should be a slight blue tint and a light gray film on the rotor face. The blue tint tells you the rotor has reached break-in temperature and the gray film is pad material starting to transfer onto the rotor face. This is what you are looking for."

"After the first break in cycle shown above, the brakes may still not be fully broken in. A second bed-in cycle, AFTER the brakes have cooled down fully from the first cycle, may be necessary before the brakes really start to perform well. "
so what the OP show on the pictures with those blue tint marks were caused by not fully break in? it show dots of the blue tint but not the whole rotors..
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      04-25-2009, 01:43 PM   #14
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Quote:
Originally Posted by Soni View Post
so what the OP show on the pictures with those blue tint marks were caused by not fully break in? it show dots of the blue tint but not the whole rotors..
After a good bed in the rotors will have a complete and even ring of blue going around them. What the OP has is spots of brake deposit on the rotor face. These deposits create areas of higher friction vs the surrounding areas, so higher temps result in these areas. The rotors got hot enough to begin transfer, but not hot enough to evenly coat the rotors.
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      04-25-2009, 04:22 PM   #15
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Quote:
Originally Posted by MteK View Post
After a good bed in the rotors will have a complete and even ring of blue going around them. What the OP has is spots of brake deposit on the rotor face. These deposits create areas of higher friction vs the surrounding areas, so higher temps result in these areas. The rotors got hot enough to begin transfer, but not hot enough to evenly coat the rotors.
Should I keep doing the bedding procedure or should I refinish my rotors and start all over again? And my goal is to have an even ring of the blue mark around the rotors not the spots like pictures I posted?
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      04-25-2009, 08:26 PM   #16
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I would try and bed them in again before taking them off and having them turned.

The results of the bed in should be a consistent blue ring around the rotor. This is a result of the entire rotor face achieving appropriate temps and not just select spots of the rotor.

Bedding in brakes is about transferring pad material to the face of the rotor and that will only occur at the appropriate temp. You need to get it there and keep it there (hence 8 runs back to back) so the transfer can be done completely.
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      04-29-2009, 07:05 PM   #17
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Am I the only one who is seeing the small stress fractures in his drill holes? My eyes aren't that bad, are they?

My recommendation would be to replace your rotors and get non-drilled/non-slotted or at the most, get slotted. Drilled rotors generally do not last under heavy use. I can crack a brand new set in less than a day.

It almost seems like your slots are causing your pad to vibrate on the rotor surface, resulting in the pad skipping across the rotor surface. Once you get uneven deposit, the problem just gets worse and worse.

What you can do to "clean" rotors is slap on a set of full race pads and do a few medium brake applications with cold rotors/pads. A cold race pad will scrape off all your deposits quite well. After a track day, I'll run my race pads on the street all the way home so the race pad deposits can get scraped off prior to going back to my street pads.

The Hawk Blues are really really abrasive when cold, fyi.
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      05-02-2009, 08:07 PM   #18
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Quote:
Originally Posted by leftcoastman View Post
Am I the only one who is seeing the small stress fractures in his drill holes? My eyes aren't that bad, are they?

My recommendation would be to replace your rotors and get non-drilled/non-slotted or at the most, get slotted. Drilled rotors generally do not last under heavy use. I can crack a brand new set in less than a day.

It almost seems like your slots are causing your pad to vibrate on the rotor surface, resulting in the pad skipping across the rotor surface. Once you get uneven deposit, the problem just gets worse and worse.

What you can do to "clean" rotors is slap on a set of full race pads and do a few medium brake applications with cold rotors/pads. A cold race pad will scrape off all your deposits quite well. After a track day, I'll run my race pads on the street all the way home so the race pad deposits can get scraped off prior to going back to my street pads.

The Hawk Blues are really really abrasive when cold, fyi.
I don't understand why it only vibrate after few medium brakes. I don't feel vibration when I do daily drive. Does Hawk make pads for Rotora BBK? I only track (lapping) the car 4-5 times per year, what color should I get for street/track?
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      05-02-2009, 08:25 PM   #19
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Yes, for the Rotora 6 piston, it's the same pad as the Stoptech ST-60. That means it's the HB-109 shape. The maximum thickness that will fit is 0.75 inches (pad material + backing plate).

It doesn't take long to cause material transfer. Especially if you're running street pads. Even on my race pads (DTC-70 Hawk Compound), it only takes about 3 laps to get me the necessary pad transfer.

It's going to be really hard to get a combo pad. If you run the HPS, you will most likely exceed the pads' max operating temp very quickly. The HP+ is slightly better, but you'll probably have the same problem. Anything more aggressive and they won't work worth crap on the street and will chew up your rotors.

And honestly, with your drilled rotors, if you try to run race pads, your drilled rotors will probably crack within one weekend. Having gone down the cosmetic route, you're kinda stuck with running street pads and just driving really slow and easy on track. Sorry.
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