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Rust on Brake Rotors

Discussion in 'Model S: Interior & Exterior' started by KeithE, Dec 8, 2013.

  1. KeithE

    KeithE Member

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    My MS is just over 10k miles and I'm loving it! One of the few problems, albeit minor, I've noticed constant rust buildup on the rotors. Does everyone else notice this? Perhaps it's the earlier vins. It seems to come off when I take to the car wash but curious if there is anything to prevent it or are these a cheap design? I don't recall so much rust in any of my other cars. Any suggestions?? Thx
     
  2. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    The Model S uses the friction brakes far less than other cars there is not as much brake action to scrub off the rust. Because brake rotors are bare steel, there is nothing you can do other than shift to N and brake hard every so often. It's not a cheap design; Brembo brakes are used by many of the top vehicle manufacturers.
     
  3. Doug_G

    Doug_G Lead Moderator

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    I find the pads scrub enough to keep the parts of the rotor that actually touch the pads quite clean. Just a couple of touches of the brake is all it takes to keep them shiny, even in salty winter conditions. (They are WAY better than the Roadster's disks - one rain shower and your rotors are brown. Stock pads don't clean it off. Have to use aftermarket pads to get decent braking.)

    However the parts of the rotor that are not involved in friction braking do get a brown rust coating on them over time. I'm not sure I've ever seen a car where this doesn't happen, though the design of the Model S wheels makes it easy to see. If you don't like it you might be able to use some of that high temperature paint that people put on their calipers.
     
  4. mknox

    mknox Well-Known Member

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    In the driveway last summer, I could literally see the rotors turn brown in real time after getting them wet with the hose while washing the wheels. I've never seen anything like that before. They would make scraping noises for the first couple of stops afterwards and then would be all shiny again.
     
  5. towman26

    towman26 Member

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    I get it after a rain or a wash but the first drive they are silver again. But I never would subject my MS to a car wash lol
     
  6. mknox

    mknox Well-Known Member

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    If I lived in Florida (and I was born in Ft Lauderdale) I wouldn't either, but here in the north, there isn't much of a choice if you want to get the road salt and grime off in sub-freezing temps. I usually go to the coin-op "spray-it-yourself" places during the winter months.
     
  7. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    I think the only real cure is to get the aero wheels so you don't see them :)
     
  8. Frankydude

    Frankydude Member

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    I did disassemble one rotor of the S of my friend, Sylvain, and paint it with a high temperature (with ceramic particles) paint, made especially
    for high temp. applications: exhausts, calipers, etc.
    This makes it possible to compare the rusting of the painted rotor with the rotor of the other wheel, on the passenger side.

    The results are positive: there is some rust building around the non-frictions surfaces, while the sames surfaces stay unrusted on the
    painted rotor.
    if paint is spread on the friction surfaces, it will be scrubbed off in the normal use, by the pads.

    To remove the rotors require to put a jack under the car, remove the wheel, remove a little nut that holds the rotor on the hub,
    remove the 2 nuts holding the Brembo caliper, and the rotor then can be removed.
    It took me about 20 minutes to arrive at that point.

    PRECAUTION: when the key remote is sensed, the car powers on and APPLIES BRAKE PRESSURE!!!
    you must put your keyfob at a sufficiently remote location so that the car doesn't sense it while working on the S.

    I did also paint the hub bearing surfaces, and put some clear coat on the inside surface of the wheel, where the wheels
    mates with the rotor.

    It is a job for a DIYer, I don't know of any garage who does this.

    My wife and I both owns Chevrolet Volts, and I did the same process to our Volts, with great success to keep the brakes
    in a pristine look.

    Hope this helps,

    Francois
    B2653
     
  9. Gizmotoy

    Gizmotoy Active Member

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    You painted your friend's rotors, and in particular the friction surface of the rotors?!?

    This is an extremely bad idea for several reasons:
    1) Rotors are made to dissipate heat. Painting a rotor inhibits its ability to keep cool by changing the heat transfer properties of the surfaces.
    2) All that paint from the friction surface is now embedded in your brake pads. This will affect stopping distances, as you've essentially glazed the brake pads with paint.
    3) Paint can affect the structural integrity of metal, particularly once the metal is exposed to high pressure and temperature.

    Worst of all, you did this on one side of the car and not the other. If your friend slams on his brakes and and the braking of the painted rotor is affected in any way, the stability of the car and your friend's life is in danger.

    There is a reason you don't know of any garage that does this, because it's dangerous.
     
  10. strider

    strider Active Member

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    He didn't paint the friction surface. He said "if paint is spread on the friction surfaces.." and means overspray. He's from Montreal so English may be a second language. Though I agree he should have masked it.

    This whole thread is about rust build-up on the non-friction surfaces of the rotors and Frankydude posted his way of fixing it. For everyday driving I doubt the heat transfer capabilities have been significantly changed. I'm sure he didn't paint down in between the two friction surfaces (the "vented" part of the rotor) so that's a ton of surface area for heat dissipation.

    So let's keep the whole "you're going to die!!!!!!" stuff to a minimum considering he's already done it on both his own cars and is still alive to post here on TMC.

    Frankydude, maybe you can post some pics for us?
     
  11. Gizmotoy

    Gizmotoy Active Member

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    Even assuming this is what was meant, he still has brake pads glazed with (some?) paint on one side and normal pads on the other side. Not good.

    Getting away with something a couple times is not really evidence of it being a good idea, but my main concern was that one pad had sucked up an entire rotor-full of paint while the other side's pad was undamaged. If it's overspray as you speculated, then it's certainly not as dire, though probably still dangerous.

    If you just daily drive at reasonable speeds, and somehow paint the hat and the edges without getting down into the vents, you'll probably suffer no ill repercussions. But you definitely shouldn't let any paint get on the friction surface, even overspray, and you absolutely should not do anything that could affect one side of the car and not the other no matter what speeds you're driving.
     
  12. Frankydude

    Frankydude Member

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    HI!
    For the paint on the friction surfaces of the rotor, I do confirm that I am talking about a bit
    of overspray. But I do confirm that I also paint the inside surfaces of the rotors
    (the vents in between the two friction surfaces).

    The theoric glazing that gizmotoy warns about is non existant: the resistance of the paint,
    compared to the hardness of the rotor and pad materials makes it to be removed very very
    quickly. Normal wear of the pads will also remove any paint that could be incrusted on the pad surface.

    On the aspect of the thermal resistance brought in by the paint: I do think that it is extremely
    minimal. A painted car will take the ambiant temperature. If paint was a so good thermal insulation,
    there would be noticeable temperature differences between the inside of a car and the oustide ambiant
    temperature. What is the R factor of less than 1 mil of paint???
    For the sake of scientifically backing my point that paint is not a thermal insulation I would like to
    present to the reader this technical report from the cold climate housing research center on tests made
    on insulating (supposedly) paint...
    http://cchrc.org/docs/reports/Insulating_Paint_Final.pdf
    Please take a read on this interesting piece of information above.
    If you have a different opinion, I would appreciate you back it up with some scientific data/reports/experience.

    For the pictures of the Tesla S rotors, I will have my friend come visit me friday. I will be able to take pictures
    on both sides, through the wheel, and repost back. One will be able to appreciate the difference of rusting between
    the two rotors.

    For the pictures on my Volt, you can take a look at this article:
    http://roulezelectrique.com/la-corrosion-de-2-metaux-differents/
    The pics were taken in november 2012, before and right after painting application.
    On can see the light overspray on the rotor. This overspray is long gone.

    My friend's Tesla is used extensively. He did also participate on a electric car acceleration
    day event at Montreal's Icar, and the brakes, althrough abused, did function normally.

    Because the rotor is made of steel, and the wheel is made of aluminum, there is galvanic
    corrosion taking place. Especially in salt country - Montreal is the best for salt!
    To avoid this, I placed a gasket of dielectric material in sandwich between the wheel and the rotor on my Volt.
    it's about 2 mills thick.
    I also replaced the steel nuts of my Volt by aluminum nuts. The results against corrosion are impressive:
    there is none! (Please take note that Porsche uses aluminum lug nuts since the `90s).
    You can take a look at pictures before and after on page 1 and 4 of this post:
    http://gm-volt.com/forum/showthread.php?21922-Wheel-corrosion-because-of-two-different-metals-...

    When I presented my solution, I also got some doomsayers comments.
    Well, none of the predicted catastrophies did materialize. :)
    And rotors are still nice, shiny and... rust free!

    Francois
    B2653
     
  13. Frankydude

    Frankydude Member

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    I wrote a more extensive reply this morning, but it seems it awaits moderator approval, as I am a
    new member on TMC.

    @gozmotoy: What would be the thermal insulation given by a coat of paint? Would you have some datas or
    technical references about this? My knowledge is that paint does not (or very minimally) give a thermal insulation.

    As strider wrote, we are talking about minimal overspray on the friction surfaces of the rotor.
    That overspray is now long gone. My Friend's Tesla was even used on Montreal ICar acceleration track, after the paint job.

    Francois
    B2653
     
  14. Gizmotoy

    Gizmotoy Active Member

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    About 50% of heat transfer out of a rotor is radiation, which can be impacted by paints and coatings. Indeed there are certain coatings that, when applied in black to enhance radiation, actually improve the heat transfer properties of brake rotors. Dacromet and Geomet both offer such a coating for use on high-end metal rotors. That said, the ones I've seen only coat the visible portions of the rotor (hat and edge vanes), not the interior cooling vanes in the center.

    One of StopTech's engineers mentioned on a racing forum I frequent that if you choose your paint carefully such that it doesn't act as a thermal insulator (high temp, ceramic-infused), and if you only paint the exterior non-friction surfaces, you'll probably be fine on the track (so daily driving should be safe). I'll dig it up this evening after work.

    Again, though, the primary issue I was concerned about is that one pad may be contaminated and the other is not, for the same reason you never replace one tire, and it takes very, very, little to contaminate a brake pad. Even that initial scraping off of rust after a car wash/rain impacts braking. Fortunately oxidation doesn't melt and sit in the organic pad material and is quickly worn away by grinding back on the rotors, so it's not a problem past the first few pushes of your brakes. While no longer on the rotors, that "long gone" paint may have been absorbed into your pad material.

    That in mind, when you do the other rotors, take a peek at those pads to make sure they're not worn smooth near the leading edge where they came in contact with the paint. I'd mask the others off when you do them.
     
  15. Frankydude

    Frankydude Member

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    For the discussion about heat dissipation of the brakes, I learned that heat is dissipated by the 3 following ways:
    Conduction, Convexion, and Radiation.
    On the radiation front, and reading from the referenced study about supposedly thermally insulating paint (that is not),
    since the main heat is located directly at the friction surfaces of the rotor, and because of the normal pad abrasion of the
    surface, there is no paint on those surfaces and thus the radiation heat transfer is mostly unmodified.

    For painting the vents in the rotors, well, the radiation has little to do in there to help to cool brakes: it radiates towards the other
    hot friction surface! The vents mostly use conduction to air to transfer heat, and painting them might even help, as rust
    builds a less heat conductive surface over the vent's steel.

    The wheel itself is a huge heat sink (and uses conduction and radiation to dissipate heat).
    It also protects the wheel bearings against big temperatures increases from the rotor's heat.

    My friend did came today with it's S, but it was too cold to go out and take pictures.
    Plus, my two previous posts were awaiting moderator approval for hours, so I thought I was
    banned or blocked from replying. That is for sure not much motivating to post pictures...

    However, he confirmed that the painted rotor does not rust, while the unpainted ones do.
    He wishes that we paint the remaining rotors on his S, when the weather will be warmer, in the spring.
    I will ask him to send me pictures of both sides, so I can post them on.

    I will research some more about the brake pad contamination, and will check if paint is an effective contaminant
    or not. If other has info about this, I would invite them to chime in!


    Francois
    B2653

    - - - Updated - - -

    I googled painting disk rotors and found this other thread about rust on rotors,
    that is avoided after painting, with numerous pictures to describe the results.
    http://g35driver.com/forums/g35-sedan-v36-2007-08/378944-brake-rotor-caliper-paint-no-more-rust.html

    Found lots of info about pad contamination through brake fluid, oil and grease, but nothing about
    paint contamination of the pads.

    Francois
    B2653
     
  16. dgmanny

    dgmanny Member

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    Has anyone experienced the brakes sticking after parking the car overnight after a rainy day? I have to give the car some extra power to break them free to start moving. Could this be rust build up?
     
  17. Gizmotoy

    Gizmotoy Active Member

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    This is common for disc brakes. Some cars are more susceptible to it than others. Rust had formed between your brake pads and the rotor's friction surface. If the oxidation is thick enough, sometimes you need to give it a bit of gas to break them free. The first stop or two knocks it all off. Nothing to worry about.
     
  18. N4HHE

    N4HHE Member

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    I find the more open the fancy wheel the faster the brake rotors rust. Rotors covered by cheap steel wheels with hubcaps rust the least.

    Pulled the wheel off a friend's car which had sat out in the rain for a couple of days. Obvious rust on his rotor. Was a bit surprised the inside surface had almost no rust. Thats when I realized it was the exposure through the open wheel rusting the rotors. The backside had a plate or shield about 1/2" off the rotor. I presume that shield was keeping wet air from directly hitting the rotor.
     
  19. Frankydude

    Frankydude Member

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    I also agree with N4HHE: less splashing water on the rotors will diminish the oxidation process.

    Francois
    B2653
     
  20. austinEV

    austinEV Active Member

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    Every time! After any rain or a wash. I have to give it a bit of a push and it lurches a bit and there is an uncomfortable crunch, like you broke off the rust or crunched a small animal... So far it has always been the rust.
     

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