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  • FIRST POST
    • sevenhills
    • By sevenhills 10th Sep 17, 8:17 PM
    • 710Posts
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    sevenhills
    Brake discs rusting
    • #1
    • 10th Sep 17, 8:17 PM
    Brake discs rusting 10th Sep 17 at 8:17 PM
    Why do brake discs rust?

    I have one disc that is rusting on the edge, as others on here have had similar issues, I thought I would ask if it be avoided.
    I recently put new pads in, cleaned the disc a little with emery paper and a file. But the rust is still a thick ridge.
    As I have alloy wheels, I can see that because the disc has a ridge, the new pads are not touching a small section near the rust, so the rust will be spreading.
    Not sure if it would have been practical to remove the discs, with the pads (Megane 2006), but renewing the pads is making the rust worse.

    I changed the pads about a month ago, and the pads have not yet worn past the ridge of rust. At the moment, the rust is minor. the car has recently past its MOT.

Page 1
    • Warwick Hunt
    • By Warwick Hunt 10th Sep 17, 8:25 PM
    • 590 Posts
    • 304 Thanks
    Warwick Hunt
    • #2
    • 10th Sep 17, 8:25 PM
    • #2
    • 10th Sep 17, 8:25 PM
    Why do brake discs rust?

    I have one disc that is rusting on the edge, as others on here have had similar issues, I thought I would ask if it be avoided.
    I recently put new pads in, cleaned the disc a little with emery paper and a file. But the rust is still a thick ridge.
    As I have alloy wheels, I can see that because the disc has a ridge, the new pads are not touching a small section near the rust, so the rust will be spreading.
    Not sure if it would have been practical to remove the discs, with the pads (Megane 2006), but renewing the pads is making the rust worse.

    I changed the pads about a month ago, and the pads have not yet worn past the ridge of rust. At the moment, the rust is minor. the car has recently past its MOT.
    Originally posted by sevenhills

    It's probably something to do with them being made from iron.
    • sevenhills
    • By sevenhills 10th Sep 17, 8:26 PM
    • 710 Posts
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    sevenhills
    • #3
    • 10th Sep 17, 8:26 PM
    • #3
    • 10th Sep 17, 8:26 PM
    It's probably something to do with them being made from iron.
    Originally posted by Warwick Hunt
    Many just wear out.

    • martinthebandit
    • By martinthebandit 10th Sep 17, 8:30 PM
    • 3,299 Posts
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    martinthebandit
    • #4
    • 10th Sep 17, 8:30 PM
    • #4
    • 10th Sep 17, 8:30 PM
    It's probably something to do with them being made from iron.
    Originally posted by Warwick Hunt

    .......and made worse if the OP doesn't do many miles.

    .......and as it's an 11 year old Renault that's quite likely.
    Politics -
    from the words Poli, meaning many
    and tics meaning blood sucking parasites


    (thanks to Kinky Friedman (or Larry Hardman) for the quote}
    • forgotmyname
    • By forgotmyname 10th Sep 17, 8:47 PM
    • 26,034 Posts
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    forgotmyname
    • #5
    • 10th Sep 17, 8:47 PM
    • #5
    • 10th Sep 17, 8:47 PM
    Fit new discs sorted until next time.
    Punctuation, Spelling and Grammar will be used sparingly. Due to rising costs of inflation.

    My contribution to MSE. Other contributions will only be used if they cost me nothing.

    Due to me being a tight git.
    • Ebe Scrooge
    • By Ebe Scrooge 10th Sep 17, 11:50 PM
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    Ebe Scrooge
    • #6
    • 10th Sep 17, 11:50 PM
    • #6
    • 10th Sep 17, 11:50 PM
    Fit new discs sorted until next time.
    Originally posted by forgotmyname
    I'll second this. Discs do wear and get rusty, it's a fact of life. They're also cheap and very easy to replace on most cars.
    I may not know much about art, but I know what I like.
    • treboeth
    • By treboeth 11th Sep 17, 12:24 AM
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    treboeth
    • #7
    • 11th Sep 17, 12:24 AM
    • #7
    • 11th Sep 17, 12:24 AM
    Fit new discs sorted until next time.
    Originally posted by forgotmyname
    So my car has surface rust on the discs after 24hours, should I change them?
    Or just take the car for a spin and clean the surface rust off?

    New discs with only a few thousand miles on and it`s a known issue on this model and many others.
    • Iceweasel
    • By Iceweasel 11th Sep 17, 8:36 AM
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    Iceweasel
    • #8
    • 11th Sep 17, 8:36 AM
    • #8
    • 11th Sep 17, 8:36 AM
    Light surface rust that gets rubbed off after a few miles/applications of the brakes is normal and not a problem.

    I think that the OP's problem is that there is a wear ridge on the outer circumference of the disc that is preventing the new pad from contacting the disc surface near the ridge.

    A visible ridge that cannot be sanded or filed off likely means that the disc is at or near the wear limit / minimum thickness.

    All discs have the minimum thickness stamped on them - perhaps difficult to see or read after corrosion has set in though.

    If I was the OP I would have fitted new discs at the same time as changing the pads.

    As Ebe Scrooge has said they are cheap and easy to replace these days.

    Some vehicles discs do tend to rust more than others - on my Freelander 1 for example I needed a new set of discs every 2nd pad change.
    • iltisman
    • By iltisman 11th Sep 17, 9:33 AM
    • 2,311 Posts
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    iltisman
    • #9
    • 11th Sep 17, 9:33 AM
    • #9
    • 11th Sep 17, 9:33 AM
    The rusting of discs does seem to vary with different vehicles I have a fairly new Fiat and an anchient SUV that do similar miles. The Fiat has been through 2 sets of discs due to rusting while the SUV is still on the originals.
    It's only my cheerfulness that keeps me going
    • andygb
    • By andygb 11th Sep 17, 12:37 PM
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    andygb
    We live in the UK, and it has been raining a lot lately.
    Rain is composed of water and various other trace elements, including salt.
    Brake discs are usually made from cast iron, and this metal does not like water, because water turns it yellow, then orange and finally a crusty brown colour, which then makes the metal corrode and fall apart.
    Lewis Hamilton and the other racing drivers get around this by fitting carbon ceramic discs, which do not rust, but which are very expensive.
    Fortunately, Lewis and the others don't have to pay for them.
    The only way to stop discs going rusty (apart from moving to the Atacama Desert), is to use the car every day and to gradually increase the braking pressure.
    When you get home, the discs will look all shiny again.
    • sevenhills
    • By sevenhills 11th Sep 17, 1:37 PM
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    sevenhills
    The rusting of discs does seem to vary with different vehicles I have a fairly new Fiat and an anchient SUV that do similar miles. The Fiat has been through 2 sets of discs due to rusting while the SUV is still on the originals.
    Originally posted by iltisman
    Perhaps if some cars have pads that leave and extra couple of mm disc showing, it can allow the rust to start?

    • decbel
    • By decbel 11th Sep 17, 1:43 PM
    • 1,494 Posts
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    decbel
    I don't do many miles in my Saxo so the discs do tend to rust. A few miles down the road and they are back to normal.

    Before my last MOT on braking they were juddering. It still passed like that.

    I got them changed anyway because it was annoying and pretty cheap.
    • Tarambor
    • By Tarambor 12th Sep 17, 6:28 PM
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    Tarambor
    I think that the OP's problem is that there is a wear ridge on the outer circumference of the disc that is preventing the new pad from contacting the disc surface near the ridge.
    Originally posted by Iceweasel
    That is usually a combination of hardened muck and rust, the solution is to get a hammer and chip away at it usually by hitting the corner edge of the disc whilst slowly rotating it until it is all gone. It is very advisable to wear eye protection.
    • Iceweasel
    • By Iceweasel 13th Sep 17, 9:15 AM
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    Iceweasel
    That is usually a combination of hardened muck and rust, the solution is to get a hammer and chip away at it usually by hitting the corner edge of the disc whilst slowly rotating it until it is all gone. It is very advisable to wear eye protection.
    Originally posted by Tarambor
    Then finish off by spinning the disc while holding a rough file at 45 degrees against the edge to remove any remaining little bits of crud/rust and to give as smooth an edge as possible.

    But don't forget to check if the disc has reached it's minimum thickness.
    • sevenhills
    • By sevenhills 13th Sep 17, 10:46 AM
    • 710 Posts
    • 256 Thanks
    sevenhills
    Then finish off by spinning the disc while holding a rough file at 45 degrees against the edge to remove any remaining little bits of crud/rust and to give as smooth an edge as possible.

    But don't forget to check if the disc has reached it's minimum thickness.
    Originally posted by Iceweasel
    I may have made the problem worse by smoothing off the rust, but its still there, so the pads are not wearing away to grip the rest of the entire disc. I guess that might happen in a few more weeks.

    • sevenhills
    • By sevenhills 13th Sep 17, 5:55 PM
    • 710 Posts
    • 256 Thanks
    sevenhills
    I think posting that for someone to read who isn't aware of brake disc rust and who could well follow that advice is akin to giving a loaded gun to a 5 year old.

    Under no circumstances ever put any kind of lubricant onto a cars brake discs.
    Originally posted by Wookey
    Its good that you have to be 16 to get a driving license

    • Richard53
    • By Richard53 13th Sep 17, 7:19 PM
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    • 2,178 Thanks
    Richard53
    I may have made the problem worse by smoothing off the rust, but its still there, so the pads are not wearing away to grip the rest of the entire disc. I guess that might happen in a few more weeks.
    Originally posted by sevenhills
    On most cars, the pad doesn't sweep the entire disc area. There is usually a small ring at the edge and another on the inside untouched by the pad. These, of course, get rusty without the pad to keep them shiny. It's absolutely normal and nothing to worry about, unless it starts to interfere with the operation of the pads. The key thing is the thickness of the disc on the shiny bit. It is quite tricky to measure this without a micrometer because of the scale built up around the edge, but it is easily done with the right measuring tools.
    An hour alone spells freedom to the slave.
    • Ebe Scrooge
    • By Ebe Scrooge 13th Sep 17, 7:54 PM
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    Ebe Scrooge
    Its good that you have to be 16 to get a driving license
    Originally posted by sevenhills
    17 for a car

    ( OK, strictly speaking, 17 to start driving on public roads )
    I may not know much about art, but I know what I like.
    • sevenhills
    • By sevenhills 13th Sep 17, 8:22 PM
    • 710 Posts
    • 256 Thanks
    sevenhills
    17 for a car

    ( OK, strictly speaking, 17 to start driving on public roads )
    Originally posted by Ebe Scrooge
    Its 16 to drive on public roads, if you are disabled

    • BeenThroughItAll
    • By BeenThroughItAll 13th Sep 17, 8:32 PM
    • 4,591 Posts
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    BeenThroughItAll
    Its 16 to drive on public roads, if you are disabled
    Originally posted by sevenhills
    Or if you want to ride a moped, or drive a tractor.
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