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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > What causes the rust?!



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      04-20-2013, 07:51 PM   #1
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What causes the rust?!

What causes the rust on the part of the rotor exposed behind the wheels, does everyone have this same problem? Car came from VA and I'm in the south, could it be related to salt and snow?

The reason I ask is because I am trying to decide if I should just clean them or clean and paint them to prevent this in the future.
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      04-20-2013, 08:15 PM   #2
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Quote:
Originally Posted by avol3xo
What causes the rust on the part of the rotor exposed behind the wheels, does everyone have this same problem? Car came from VA and I'm in the south, could it be related to salt and snow?

The reason I ask is because I am trying to decide if I should just clean them or clean and paint them to prevent this in the future.
Water + iron = rust
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      04-20-2013, 08:57 PM   #3
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after cleaning the rust put antiseize on the wheel where it touches the rotor.

You should do that even if you paint, and use high temp ceramic paint if you do
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      04-21-2013, 08:44 AM   #4
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Paint the rotors?

Did I read that correctly?

Don't put anything on your rotors... for the love of god.

A little rust on the rotors after a few days is normal for your standard factory rotors. (This happens when OXYGEN touches iron, a chemical process called oxidation. You're seeing iron oxide.)

Water has O2, and salt acts as a catalyst, these inspire oxidation.

If you put anti-seize on your rotors, your brake pads will fail to seize the rotors when you come to the first stop sign past your house.

I hope you were mistaken when you wrote "rotors"
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      04-21-2013, 08:48 AM   #5
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are you talking about the braking surface or the hat?

If the braking surface it will wipe off as soon as you start driving

If the hat the best way to deal with it is to use Centric premium rotors next time you do a brake job. I have not yet found a paint that works well... I've used the FLAPS spray can caliper paint on rotors and drums before and it's better than nothing but will not look perfect and detailed after a few months.
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      04-21-2013, 09:18 AM   #6
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its gotta be the hat, right? hope so
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      04-21-2013, 09:34 AM   #7
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      04-21-2013, 05:20 PM   #8
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Quote:
Originally Posted by MediumLebowski View Post
Paint the rotors?

Did I read that correctly?

Don't put anything on your rotors... for the love of god.

A little rust on the rotors after a few days is normal for your standard factory rotors. (This happens when OXYGEN touches iron, a chemical process called oxidation. You're seeing iron oxide.)

Water has O2, and salt acts as a catalyst, these inspire oxidation.

If you put anti-seize on your rotors, your brake pads will fail to seize the rotors when you come to the first stop sign past your house.

I hope you were mistaken when you wrote "rotors"
Not the braking surface, that wouldn't make any sense at all. I'm talking about I guess what they call the "hat" of the rotor.
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      04-21-2013, 05:22 PM   #9
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Quote:
Originally Posted by N8N View Post
are you talking about the braking surface or the hat?

If the braking surface it will wipe off as soon as you start driving

If the hat the best way to deal with it is to use Centric premium rotors next time you do a brake job. I have not yet found a paint that works well... I've used the FLAPS spray can caliper paint on rotors and drums before and it's better than nothing but will not look perfect and detailed after a few months.
Yes the hat, the rust looks horrible, I can't imagine that this just happens on all BMWs
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      04-21-2013, 05:47 PM   #10
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this?

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      04-21-2013, 07:22 PM   #11
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Quote:
Originally Posted by avol3xo View Post
Yes the hat, the rust looks horrible, I can't imagine that this just happens on all BMWs
It happens not only on all BMWs but pretty much all cars!
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      04-21-2013, 07:28 PM   #12
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Quote:
Originally Posted by avol3xo View Post
What causes the rust on the part of the rotor exposed behind the wheels, does everyone have this same problem? Car came from VA and I'm in the south, could it be related to salt and snow?

The reason I ask is because I am trying to decide if I should just clean them or clean and paint them to prevent this in the future.
chemistry. if you want it to be rust free, you need to move somewhere without water or oxygen.
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      04-21-2013, 09:16 PM   #13
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Quote:
Originally Posted by N8N View Post
It happens not only on all BMWs but pretty much all cars!
Never saw this on either of my Hondas, or any of my parents' cars. (Acura, Merc)
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      04-21-2013, 09:18 PM   #14
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Quote:
Originally Posted by VTECaddict View Post
chemistry. if you want it to be rust free, you need to move somewhere without water or oxygen.
I could do without the smart ass comments, I'm asking this because I have never seen it this bad on any other car before, but I have seen a couple of people here mention it, just trying to see what I can do to stop or slow it down. I just sold a car I owned for 8yrs and never saw this. Yes there were hints of rust on the stopping surface but they came clean after using the brakes.
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      04-21-2013, 09:23 PM   #15
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Originally Posted by MediumLebowski View Post
this?

The part that is painted on these rotors is what I am talking about, but I want to keep my stock rotors just wondering how I can get these looking new again for as long as possible.
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      04-22-2013, 08:10 AM   #16
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Quote:
Originally Posted by avol3xo View Post
Never saw this on either of my Hondas, or any of my parents' cars. (Acura, Merc)
Must be climate difference, I'm guessing you never see snow/road salt or much rain for that matter? My '09 looks like it was pretty well pampered by PO and even it is showing signs of some surface rust on the rotor hats. It's apparently been in NoVA since delivery.

My Jeep lived for 10 years or so in Pittsburgh; the rotors were pretty crusty when I replaced them. The rear drums didn't need replacing so I cooked all the heavy flaky rust off of them in my electrolytic tank (if you work on old cars you really should set one up, it's magical) and painted them with high-temp caliper paint from the parts store; you couldn't ask for better surface prep but it's only be about 6 months and already there's some rust showing through the paint. IME it's something you just have to live with and either ignore, repaint 2x a year, or never drive your vehicle in rain (I really didn't drive the Jeep in snow that much this year.)

Now I did use Centric Premium rotors on the Jeep and it's only been a little over a year but the hats still look good, so they may be my go-to rotor going forward. I see they have a "high-carbon" version now as well. I believe that StopTech are made by Centric if you like drilled and/or slotted.

Last edited by N8N; 04-22-2013 at 08:19 AM.
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      04-22-2013, 08:54 AM   #17
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The rust bleeds from the bearing hub since BMW leaves it as just unfinished steel/iron. Paint it when the car is brand new and you will eliminate most of the rust.
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      04-22-2013, 09:17 AM   #18
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Quote:
Originally Posted by velvetaudio View Post
Here's a way to clean the rust off:
http://www.e90post.com/forums/showthread.php?t=26398

Here's how to paint the calipers and hubs:
http://www.e90post.com/forums/showth...ight=paint+hub
found this
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      04-22-2013, 12:13 PM   #19
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Quote:
Originally Posted by Deepti
Water and iron when get mix both than become rust, you can do rust free paint.
Thanks!
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      04-22-2013, 12:14 PM   #20
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Quote:
Originally Posted by N8N

Must be climate difference, I'm guessing you never see snow/road salt or much rain for that matter? My '09 looks like it was pretty well pampered by PO and even it is showing signs of some surface rust on the rotor hats. It's apparently been in NoVA since delivery.

My Jeep lived for 10 years or so in Pittsburgh; the rotors were pretty crusty when I replaced them. The rear drums didn't need replacing so I cooked all the heavy flaky rust off of them in my electrolytic tank (if you work on old cars you really should set one up, it's magical) and painted them with high-temp caliper paint from the parts store; you couldn't ask for better surface prep but it's only be about 6 months and already there's some rust showing through the paint. IME it's something you just have to live with and either ignore, repaint 2x a year, or never drive your vehicle in rain (I really didn't drive the Jeep in snow that much this year.)

Now I did use Centric Premium rotors on the Jeep and it's only been a little over a year but the hats still look good, so they may be my go-to rotor going forward. I see they have a "high-carbon" version now as well. I believe that StopTech are made by Centric if you like drilled and/or slotted.
Never any snow down here, I can count on one hand how many times I have driven in snow, and no salt of course. Thanks for the suggestions.
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      04-22-2013, 12:16 PM   #21
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Quote:
Originally Posted by David1
The rust bleeds from the bearing hub since BMW leaves it as just unfinished steel/iron. Paint it when the car is brand new and you will eliminate most of the rust.
I've got almost 20k mi now, but hopefully cleaning and painting them now will keep them looking good for a while.
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      04-22-2013, 12:17 PM   #22
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Quote:
Originally Posted by idrift4wd
Quote:
Originally Posted by velvetaudio View Post
Here's a way to clean the rust off:
http://www.e90post.com/forums/showthread.php?t=26398

Here's how to paint the calipers and hubs:
http://www.e90post.com/forums/showth...ight=paint+hub
found this
Thanks for this, exactly what I was looking for.
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