Black spots or "hot spots" on the rotor

DaFish · 03-31-2013, 03:34 PM

I put on Stoptech Cryo slotted rotors last fall. I have on my front left rotor 2 black spots now on them.

I am noticing that the car HUMS when I heat the brakes up really hot. Like repeated stops on the highway from 140 km/hour (80-90 mph). This is really annoying and I thought this was from the slotted rotor.

The brakes work fine, stop straight, no pull... but hum - only when hot.

1) What can I do about it?
2) what is it caused from?

Thanks in advance.

jpirelli · 04-01-2013, 10:23 AM

Slotted rotors make noise

DaFish · 04-01-2013, 12:25 PM

Quote:

Originally Posted by DaFish

I put on Stoptech Cryo slotted rotors last fall. I have on my front left rotor 2 black spots now on them.

I am noticing that the car HUMS when I heat the brakes up really hot. Like repeated stops on the highway from 140 km/hour (80-90 mph). This is really annoying and I thought this was from the slotted rotor.

The brakes work fine, stop straight, no pull... but hum - only when hot.

1) What can I do about it?
2) what is it caused from?

Thanks in advance.

Here is the Picture of the spot.

DaFish · 04-01-2013, 12:27 PM

Quote:

Originally Posted by jpirelli

Slotted rotors make noise

I read that AFTER I bought and installed the slotted rotors. I would NOT have bought them if I knew that. Drilled or stock would have been fine. The car is 99% daily driven so this is annoying and a bad move on my part.

I thought I did my homework too.... sucks.

cvc 22349a · 04-01-2013, 02:13 PM

Quote:

Originally Posted by DaFish

I read that AFTER I bought and installed the slotted rotors. I would NOT have bought them if I knew that. Drilled or stock would have been fine. The car is 99% daily driven so this is annoying and a bad move on my part.

I thought I did my homework too.... sucks.

I thought someone suggested oem rotors

ot but I'm curious about the stoptech pads. How do they compare to oem/would you buy them again?

techwhiz · 04-01-2013, 05:52 PM

OEM Z4 35is rotors.
They are floating with aluminum hats.

El Cheapo Loco · 04-01-2013, 06:20 PM

Quote:

Originally Posted by jpirelli

Slotted rotors make noise

Nice to know. Thanks for the heads up.

r1concepts · 04-01-2013, 06:20 PM

This is caused by very aggressive braking. You can remove these spots by doing a braking procedure to slightly remove the spots.

vasillalov · 04-01-2013, 06:28 PM

Quote:

Originally Posted by r1concepts

This is caused by very aggressive braking. You can remove these spots by doing a braking procedure to slightly remove the spots.

Correct! I've had something similar happen to me when I was bedding in a fresh set of PFC 08s (track compound) on a brand new set of OEM rotors. After just few laps on the track, these black spots went away.

DUI Elite · 04-01-2013, 06:31 PM

Mine hum and are also slightly warped (shake my steering wheel a little bit).

I will never again buy ECS rotors. I am not suprised about the hum, as it makes sense that they would since theres gaps in the rotor, however them being warped already is pissing me off.

Are your stoptech's warped at all?

BillionPa · 04-01-2013, 08:46 PM

The hum is the sound of them outgassing, it means the slotted parts are doing their job

The cryo treatment probably saved your rotors, in most cases if rotors get hot enough to cause spots like that, they warp to hell and back. More than likely you need a more thermally agressive pad compound to keep up with your braking habits, what are you currently running? the stoptechs?

DUI Elite · 04-01-2013, 09:14 PM

Quote:

Originally Posted by BillionPa

The hum is the sound of them outgassing, it means the slotted parts are doing their job

The cryo treatment probably saved your rotors, in most cases if rotors get hot enough to cause spots like that, they warp to hell and back. More than likely you need a more thermally agressive pad compound to keep up with your braking habits, what are you currently running? the stoptechs?

This makes sense.

Thank you for the explanation

Meeni · 04-02-2013, 12:04 AM

Your picture shows severe pad marking. Do not keep brakes applied while stoped after braking very hard.

If you ever start feeling pulsating brakes or steering woble, have your rotors resurfaced first as it is probably the issue. Might go away by itself if you are lucky.

03-31-2013, 03:34 PM	#1
DaFish Major 157 Rep 1,288 Posts Drives: 2014 435iX, FBO Join Date: Mar 2009 Location: Ontario, Canada iTrader: (0) Garage List 2014 BMW 435i Xdrive [0.00]	Black spots or "hot spots" on the rotor - what is it from? I put on Stoptech Cryo slotted rotors last fall. I have on my front left rotor 2 black spots now on them. I am noticing that the car HUMS when I heat the brakes up really hot. Like repeated stops on the highway from 140 km/hour (80-90 mph). This is really annoying and I thought this was from the slotted rotor. The brakes work fine, stop straight, no pull... but hum - only when hot. 1) What can I do about it? 2) what is it caused from? Thanks in advance. __________________ 2020 M2 Competition HS, DCT, 763s, Carbon: splitter, side skirt, grill, diffuser, wing Previous: 2014 BMW F32 435iX - JB4, MHD Flash, BMS Meth Kit, ER Intercooler, intake, catless DPs, KW Streets, 437M Reps with 245/35 and 275/30 Michelin PSS 4S
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04-01-2013, 10:23 AM	#2
jpirelli Power is nothing without control 33 Rep 762 Posts Drives: E90 + E92 Join Date: Apr 2009 Location: Southeast/Southwest iTrader: (3)	Slotted rotors make noise
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04-01-2013, 05:52 PM	#6
techwhiz Colonel 453 Rep 2,973 Posts Drives: e90 335i Sedan - Arctic Join Date: Feb 2012 Location: Bay Area, Ca iTrader: (4)	OEM Z4 35is rotors. They are floating with aluminum hats.
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04-01-2013, 06:20 PM	#8
r1concepts Lieutenant Colonel 90 Rep 1,677 Posts Drives: 07' E90 335i Join Date: Jul 2009 Location: Cerritos, CA iTrader: (2)	This is caused by very aggressive braking. You can remove these spots by doing a braking procedure to slightly remove the spots.
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04-01-2013, 06:31 PM	#10
DUI Elite ///M at Heart 90 Rep 1,954 Posts Drives: 06 SGM E90, 15 BSM E84 Join Date: Jan 2011 Location: Chicago, IL iTrader: (4)	Mine hum and are also slightly warped (shake my steering wheel a little bit). I will never again buy ECS rotors. I am not suprised about the hum, as it makes sense that they would since theres gaps in the rotor, however them being warped already is pissing me off. Are your stoptech's warped at all?
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04-01-2013, 08:46 PM	#11
BillionPa Second Lieutenant 2 Rep 288 Posts Drives: 335i Join Date: Feb 2013 Location: USA iTrader: (0)	The hum is the sound of them outgassing, it means the slotted parts are doing their job The cryo treatment probably saved your rotors, in most cases if rotors get hot enough to cause spots like that, they warp to hell and back. More than likely you need a more thermally agressive pad compound to keep up with your braking habits, what are you currently running? the stoptechs?
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04-02-2013, 12:04 AM	#13
Meeni Gateropode 329 Rep 2,848 Posts Drives: BMW 330i 06 Join Date: Apr 2012 Location: TN iTrader: (0)	Your picture shows severe pad marking. Do not keep brakes applied while stoped after braking very hard. If you ever start feeling pulsating brakes or steering woble, have your rotors resurfaced first as it is probably the issue. Might go away by itself if you are lucky.
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