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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Front brakes started smoking



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      02-14-2013, 01:11 AM   #1
kkashanchi
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Front brakes started smoking

Hey guys, after some aggressive driving and a very hard stop going down a hill my brakes started to smoke like crazy. There seemed to be no ill- effects performance wise immediately but now, 3 months later, the BRAKE light has been illuminated in red and will not go away. I checked the pads and there is plenty of pad left, but on the front pads there are a discoloration (almost like a gray area or where it could have caught fire). I don't think the rotors are glazed because they look normal and I am wondering what the cause of this BRAKE light can be. Recently, the brake pedal has required more travel and lacks bite along with braking performance. I'm going to replace my brake fluid (just rolled over 30k miles and the red car on a lift symbol is showing) and hopefully this will fix the problem. The fluid level is not too low but isnt at max. Should i replace my pads or not?
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      02-14-2013, 06:44 AM   #2
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Pads (front) sound glazed and fluid was probably boiled. Bleed it right away, and if the pads have a smooth shiny surface, either get them cut down, or replace them (replace is easier and probably good insurance). Do the rotors have an uneven color on them, or do you see any "smeared" on the surface? Does your pedal ever pulsate when you apply the brakes?

As for the brake light, I'll let someone not as new to BMWs surmise what that means. I'd just be guessing.
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      02-14-2013, 06:28 PM   #3
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Quote:
Originally Posted by ashmostro
Pads (front) sound glazed and fluid was probably boiled. Bleed it right away, and if the pads have a smooth shiny surface, either get them cut down, or replace them (replace is easier and probably good insurance). Do the rotors have an uneven color on them, or do you see any "smeared" on the surface? Does your pedal ever pulsate when you apply the brakes?

As for the brake light, I'll let someone not as new to BMWs surmise what that means. I'd just be guessing.
The rotors looks normal and the brake never pulsates, I'll try to take off the front pads this weekend and take a look at them to see if they're smooth and shiny. Thanks for your help!
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      02-14-2013, 09:35 PM   #4
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I ran my stock pads on the track until they started disintegrating due to excessive heat; they were white around the edges and chipped/chunked. In addition to doing that, I'm in agreement you probably boiled the brake fluid.

The red BRAKE light is related to the brake sensors; the sensors are designed to trip when the pads get down to a certain thickness (the sensor wears down with the pad and the connection eventually breaks, triggering the light). The sensors also trip however due to heat.

I concur with ashmostro; get the pads replaced and the sensors while you're at it (sensors are cheap). The rears might be OK (the front brakes do most of the work), but double-check. I'd also recommend a brake fluid flush, especially if it's been a while since your last one. Boiling the brake fluid (and just time in general) reduces its effectiveness. Consider going with high-temp brake fluid, if you're going to be driving the car hard. It won't boil as easily.
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      02-14-2013, 09:42 PM   #5
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Good point... White around the edges can mean you exceeded the operating temp of the pads which may have compromised them chemically. Just replace them- and consider a more aggressive pad. If you overheated them once, you're likely to do it again.
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      02-14-2013, 09:46 PM   #6
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Quote:
Originally Posted by CJ421 View Post
I ran my stock pads on the track until they started disintegrating due to excessive heat; they were white around the edges and chipped/chunked. In addition to doing that, I'm in agreement you probably boiled the brake fluid.

The red BRAKE light is related to the brake sensors; the sensors are designed to trip when the pads get down to a certain thickness (the sensor wears down with the pad and the connection eventually breaks, triggering the light). The sensors also trip however due to heat.

I concur with ashmostro; get the pads replaced and the sensors while you're at it (sensors are cheap). The rears might be OK (the front brakes do most of the work), but double-check. I'd also recommend a brake fluid flush, especially if it's been a while since your last one. Boiling the brake fluid (and just time in general) reduces its effectiveness. Consider going with high-temp brake fluid, if you're going to be driving the car hard. It won't boil as easily.
if pad life is okay just change the sensor. It really depends on driving. If you're tripping the traction control, rear pads will wear much much quicker.
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      02-15-2013, 02:00 AM   #7
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Quote:
Originally Posted by CJ421 View Post
I ran my stock pads on the track until they started disintegrating due to excessive heat; they were white around the edges and chipped/chunked. In addition to doing that, I'm in agreement you probably boiled the brake fluid.

The red BRAKE light is related to the brake sensors; the sensors are designed to trip when the pads get down to a certain thickness (the sensor wears down with the pad and the connection eventually breaks, triggering the light). The sensors also trip however due to heat.

I concur with ashmostro; get the pads replaced and the sensors while you're at it (sensors are cheap). The rears might be OK (the front brakes do most of the work), but double-check. I'd also recommend a brake fluid flush, especially if it's been a while since your last one. Boiling the brake fluid (and just time in general) reduces its effectiveness. Consider going with high-temp brake fluid, if you're going to be driving the car hard. It won't boil as easily.

I'm not sure if they are white, but I'm going to pull the pads tomorrow and check it out. Ill try to take pictures of what I'm talking about. Hopefully I can get away with just replace the brake fluid with some super blue lol. If I was to just replace the front brakes would it be okay to have cool carbon brake pads up front and oem brakes in the rear?
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      02-15-2013, 02:20 AM   #8
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Quote:
Originally Posted by ashmostro View Post
Good point... White around the edges can mean you exceeded the operating temp of the pads which may have compromised them chemically. Just replace them- and consider a more aggressive pad. If you overheated them once, you're likely to do it again.

can I replace just the front pads with cool carbons and leave the back with the existing oems?
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      02-15-2013, 02:23 AM   #9
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I still am hesitant to say its the pads because why would this decrease in brake-potency occur so long after they started to smoke? The BRAKE light came on last week and that is months after the front brakes started to smoke. I should have added that the red car on a lift signal is also showing and that i just rolled over 30k miles for the 30k service but I am out of warranty. Is there any way that I just need to change the brake fluid and maybe the sensors?
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      02-15-2013, 06:31 AM   #10
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Quote:
Originally Posted by kkashanchi View Post
I still am hesitant to say its the pads because why would this decrease in brake-potency occur so long after they started to smoke? The BRAKE light came on last week and that is months after the front brakes started to smoke. I should have added that the red car on a lift signal is also showing and that i just rolled over 30k miles for the 30k service but I am out of warranty. Is there any way that I just need to change the brake fluid and maybe the sensors?


Could be a variety of things causing further degradation. It's kind of academic at this point since your pads probably would benefit from being thrown in the trash, lol. If you do replace the pads only, make sure to scuff the rotors with a flex hone or an abrasive pad (not sandpaper!) if you are switching pad compounds. Hell I would do it anyway if you overheated the brakes since you could have uneven pad transfer on the rotors which can eventually lead to shuddering.

But again, at the very least you should probably bleed the lines and replace the pads with something new.
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      02-15-2013, 08:46 AM   #11
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can I replace just the front pads with cool carbons and leave the back with the existing oems?
Yes, you can use a more aggressive compound up front no problem. The other way around (using a more aggressive compound in the rear and keeping the front stock) isn't advisable though, for future reference. See my post here.
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      02-15-2013, 10:26 AM   #12
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100% agreed. I said something similar recently on another thread.

Again, remember to take down the pad transfer layer if you switch compounds but not rotors.
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      02-15-2013, 01:28 PM   #13
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thanks so much for the help guys, how do I remove the pad transfer layer exactly though? I thought the bedding in process would take care of it
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      02-15-2013, 01:49 PM   #14
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No, bedding will just put a layer on top of the layer.

You can use a brillo pad and elbow grease, a flex hone drill bit with flex hone oil (easier), or you can install racing pads and drive on the street for a weekend and their abrasive behavior at low temps will take down the transfer layer. Note that this only works with racing pads and only at low temps. Street pads will just go straight to adherent friction and you won't get this effect.
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      02-15-2013, 02:39 PM   #15
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Quote:
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No, bedding will just put a layer on top of the layer.

You can use a brillo pad and elbow grease, a flex hone drill bit with flex hone oil (easier), or you can install racing pads and drive on the street for a weekend and their abrasive behavior at low temps will take down the transfer layer. Note that this only works with racing pads and only at low temps. Street pads will just go straight to adherent friction and you won't get this effect.

I just pulled the pads and they're definitely glazed so I'm going to replace the fronts today. There is no layer on top of the rotor that I can see though, is it supposed to be visible? I can also not feel a difference from touch.
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      02-15-2013, 05:57 PM   #16
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No, it would not be visible at all. it's a microlayer of material. When you remove it though, you will see that the underlying rotor metal is much lighter in color. makes it easy to tell if you've missed a spot because it will be darker.

Again, the race pads method is the easiest, but also the most expensive.

And FYI just so you know what to look for, glazing on pad makes them *very* shiny. Almost like glassy looking. Sometimes it's easy to mistake a well-worn pad with a glazed one. Just for future info.
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      02-15-2013, 08:27 PM   #17
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If one wanted to get some race pads for the HPDE, what are some good ones and how do you break them in? Just put them on ahead of time and drive to the track? I was surfing for the options and saw some race pads with fancier but conventional material, some ceramic, some "yellow". I would just be using the OEM calipers.
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      02-16-2013, 03:21 PM   #18
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Race pads are a personal selection kind of thing. What one person loves might be another's poison. Best thing to do is start small and work your way up in price before you decide what you really want- and also see if you can drive other people's cars with various pads.

Some well-respected pad brands to start researching are:
Carbotech
Pagid
Cobalt
Hawk
EBC
Project Mu
RacingBrake
Raybestos
Mintex
and more...


As for break in, every manufacturer will recommend a different procedure for bedding in. But the basic premise is the same, and twofold:
1) Breaking in the pad is getting it up to temp so that it can "outgas" the bonding agents that are part of manufacture. That can be done either on the track by pushing until you hit "green fade" which is where the pads suddenly don't seem to be working as well, and start to smell- you pull into the pits and let them cool, or go really slow to allow airflow. Then you go back out after they've cooled completely and you will have a good pedal and that's when you can really bed them in.
2) "Bedding" the rotor which is really just putting down a good even transfer layer. This isn't that hard to do really. Just driving at 70% of max will get the temps up, but not so high that you risk smearing the pads before the rotors have time to get an even layer deposited on them. Again, after doing the initial bed, come back in, let them cool and you are good to go.

This is somewhat oversimplified since different pads and even cars are going to achieve optimal temp at different times so you really need to pay attention to the feel of the pedal, and even the appearance of the rotors.

Also, race pads at low temp are abrasive, so if you drive around town with race pads (or even slowly on the track for too long), you may end up removing the transfer layer off the rotor and then you have to do step 2 again. This is where you again should pay attention to the sounds, feel, and appearance of the rotors to know what is happening.



Good luck and feel free to ask more questions. Only way to learn! Also there are a lot of informational resource on the web if you want to google the topic and learn more.
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      02-17-2013, 06:24 AM   #19
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I would not recommend putting racing pads on a road car. They don't work we'll until they are up to operating temperature. Thus if you need to do an emergency stop and your brakes are cold you won't stop that quickly. I fast road pad will be much better.

However it sounds like your existing braking system is not working as it should. Brake fluid absorbs water over time and is recommended to be changed every 2 years. Personally I change this early. Poor break fluid will give you a sloppy pedal and when it boils you will get no/very little braking affect. To be honest BMW braking parts are good. I would replace the fluid with genuine BMW fluid and change it regularly. You won't boil this if you do that.

It takes a lot to set fire to brakes. I have only done this either on a mountain pass driving to hard down hill and on track after 20 laps of flat out driving in my e30. the mountain pass incident required new disc and pads while the track car recovered when they cooled down. If your brake pads where low they would overheat more quickly.

For what it's worth I would fit some genuine BMW brake pads and flush the brake fluid and replace. I am sure this will give you good brakes.
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      02-17-2013, 09:02 AM   #20
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Indeed race pads will not work as well as road pads on the street, by their very nature. Thanks for that responsible warning to the op.

As for whether the stock system is adequate, or if it is likely that the op overburdened his system- the fact is, there is no universal solution for brakes. One man's perfection is another's uselessly inadequate. It is heavily influenced by your driving style. I run very aggressive near-race pads on the street for that reason.

But, your points are valid and well-intentioned so I appreciate them as counterpoint. Thanks.
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