Dark spots on rear rotors

MZWIE · 11-29-2015, 07:02 PM

I'm trying to determine what is causing this (see pics). Only on the rear. Doesn't look like hot spots.

Any ideas?

Dackelone · 11-29-2015, 07:10 PM

Its called RUST! You need to drive the car more often. Maybe do a few good hard stops to clean off the rust spots.

MZWIE · 11-30-2015, 08:49 AM

Well. I drive it every day approximately 85 miles. So this is happening over night. Can't be right.

Why always the same spot and only on the back. Even after hard stops nothing is cleaned.

miro2296 · 11-30-2015, 02:12 PM

do you put your emergency brake on each time you stop?

MZWIE · 11-30-2015, 04:26 PM

I've never used the parking brake in this car. No need to.

Pig Farmer · 11-30-2015, 05:09 PM

Looks like brake pad deposits. This happens if you hold your foot down on the brakes when the rotors are hot. I use to get this all the time when I ran cool carbon pads. Once you get uneven pad transfer, the deposits can build up in the same place over time. If it starts to vibrate, or you feel thumping in the brake pedal, hit the rotors with sandpaper and re-bed the pads. You may be able to clean up the rotors by doing a series of hard braking runs, but this can sometimes add to the deposits (depending on the type of pads you are running).

BTW, don't underestimate the amount of heat generated by the rear brakes. Although the front brakes do most of the work when stopping, the rear brakes are constantly working to maintain stability (i.e. DTC).

chris82 · 12-04-2015, 02:08 PM

Quote:

Originally Posted by e34m5

Well. I drive it every day approximately 85 miles. So this is happening over night. Can't be right.

Why always the same spot and only on the back. Even after hard stops nothing is cleaned.

Is it causing any sort of problems? Anything problematic when braking? I'm a huge fan of the "if it aint broke don't fix it". If it is just a visual mark, then spending money on it is kind of silly to be frank.

MightyMouseTech · 12-04-2015, 03:15 PM

Quote:

Originally Posted by miro2296

do you put your emergency brake on each time you stop?

The parking brake does not operate the rear caliper. There is a set of brake shoes inside the rear rotor that are the parking brake.

miro2296 · 12-04-2015, 04:21 PM

Quote:

Originally Posted by MightyMouseTech

The parking brake does not operate the rear caliper. There is a set of brake shoes inside the rear rotor that are the parking brake.

You are correct sir! I've learned this after taking apart the rear

Thanks for your help by the way

MightyMouseTech · 12-04-2015, 04:46 PM

Quote:

Originally Posted by miro2296

Quote:

Originally Posted by MightyMouseTech

The parking brake does not operate the rear caliper. There is a set of brake shoes inside the rear rotor that are the parking brake.

You are correct sir! I've learned this after taking apart the rear

Thanks for your help by the way

Anytime. Glad to help.

MZWIE · 12-05-2015, 01:38 PM

Brakes work fine. Very loud thumpa thumpa sometimes.

11-29-2015, 07:02 PM	#1
MZWIE Lieutenant Colonel 388 Rep 1,660 Posts Drives: M2 Join Date: Jun 2007 Location: GEORGIA iTrader: (0)	Dark spots on rear rotors I'm trying to determine what is causing this (see pics). Only on the rear. Doesn't look like hot spots. Any ideas? Attached Images
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11-29-2015, 07:10 PM	#2
Dackelone European Editor 10589 Rep 22,992 Posts Drives: N54 e82 Join Date: Feb 2010 Location: Bayern, Germany iTrader: (1)	Its called RUST! You need to drive the car more often. Maybe do a few good hard stops to clean off the rust spots. __________________ Dackel's European Delivery Museum Guide
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11-30-2015, 08:49 AM	#3
MZWIE Lieutenant Colonel 388 Rep 1,660 Posts Drives: M2 Join Date: Jun 2007 Location: GEORGIA iTrader: (0)	Well. I drive it every day approximately 85 miles. So this is happening over night. Can't be right. Why always the same spot and only on the back. Even after hard stops nothing is cleaned.
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11-30-2015, 02:12 PM	#4
miro2296 Colonel 57 Rep 2,251 Posts Drives: '08 Montego Blue BMW 135i Join Date: Nov 2008 Location: Round Rock, TX iTrader: (1)	do you put your emergency brake on each time you stop? __________________ ------------------------------------- BMW 135i/6 Speed/Montego Blue/Formula One Ceramic Tint/JB4 G4/AA Sport Intercooler/19 inch Iconz 880Z(19X8.5 & 19X10)/PSS 225/35 & 265/30/E93 M3 front sway bar/TRW front and rear Control Arms/BMS Drop In Filter/Dinan Exhaust/BlackLines/Upgraded \\\M RSFB
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11-30-2015, 04:26 PM	#5
MZWIE Lieutenant Colonel 388 Rep 1,660 Posts Drives: M2 Join Date: Jun 2007 Location: GEORGIA iTrader: (0)	I've never used the parking brake in this car. No need to.
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11-30-2015, 05:09 PM	#6
Pig Farmer Major 340 Rep 1,293 Posts Drives: E92M Join Date: May 2010 Location: Florida iTrader: (0)	Looks like brake pad deposits. This happens if you hold your foot down on the brakes when the rotors are hot. I use to get this all the time when I ran cool carbon pads. Once you get uneven pad transfer, the deposits can build up in the same place over time. If it starts to vibrate, or you feel thumping in the brake pedal, hit the rotors with sandpaper and re-bed the pads. You may be able to clean up the rotors by doing a series of hard braking runs, but this can sometimes add to the deposits (depending on the type of pads you are running). BTW, don't underestimate the amount of heat generated by the rear brakes. Although the front brakes do most of the work when stopping, the rear brakes are constantly working to maintain stability (i.e. DTC).
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12-05-2015, 01:38 PM	#11
MZWIE Lieutenant Colonel 388 Rep 1,660 Posts Drives: M2 Join Date: Jun 2007 Location: GEORGIA iTrader: (0)	Brakes work fine. Very loud thumpa thumpa sometimes.
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