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  1. #1
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    So I got this used bike, rotors were warped, got some used rotors, swapped, seems that the right side is still warped slightly, noticeable. Just got another used set of rotors, one is obviously warped, the other seems good, on glass, put it on the bike, still slightly warped, not as bad as the previous but there none the less.

    Itís a gamble getting used, I know, but rotors are pricey, so Iím taking my chance, Iím a gambler.

    When I take the calipers off, Iím mounting a pencil, file, whatever, through one of the caliper bolt holes and spinning the wheel, looking for a rub or a gap, left side looks fine, right side has the slight warp. You can see a slight gap between the pencil point and the rotor at a certain point of the rotation.

    Iím wondering what could cause this?
    Iím assuming all these rotors are warped as Iím getting them, and not GETTING warped once I put them on.

    BUT, Could something about the rim be causing this? The mounting bolts and parts some how have something to do with it? Wheel bearings? something? I havenít ridden hard enough for heat to build. And I donít hold the brakes on at stops.

    I figure it canít be an unbalanced tire, canít be the master cylinder or calipers or bearings, because itís clearly at one point in the wheels rotation, while on the brakes. feeling slows when the bike slows, etc.

    The warp on the latest rotor I put on is felt more at slower speed, but is not as bad as the previous which was felt always on the brakes, and would cause the springs to bounce some pulling up to stops. Latest rotor you can feel it, but it doesnít do the spring diving thing, which is better, but still.....

    Iím just wondering if thereís things I can look for or should think about checking that I havenít already?

    I know I should get all new hardware, and donít get used rotors and all that jazz but, shoot...
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  3. #2
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    I'm not the mechanical source for info that other members on the forum are. But I'll pass on my thoughts and hope that someone with more experience can give you better advice.

    First, I'd wonder how much can be machined off the existing rotors? On cars they'll do this, up to the limit of the specs. It does seem strange that one side of the rotor seems even, while the other doesn't.

    Second, I'd look seriously at some after-market rotors. They'd be new and from what I can see, the cost is not bad since they don't have BMW part numbers.

    eBay has some ranging from $40 to $318. The higher cost rotors are OEM part numbers. The lower cost rotors don't say "BMW". For the cost of the lower cost rotors, you'd get new parts and not used warped parts.

    Chris
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    Your new 09' ST has floating rotors. The issue of warped rotors you describe might not actually be the rotors themselves, but rather the spindles, washers, and other parts that are supposed to move with the rotors. The rotors themselves have very little play in terms of re machining them. Very small tollerances. Most commonly, there is an issue in the sliding pieces that connect the rotors to the wheel. There is a spindle and a couple washers, one of which is a wavey washer. These need to remain clean and lubricated. The key is tightening to the proper torque that half compresses the wavey washers.

    I've tried replacing with used, just like you did. It improved things short term, but I only found long time improvement from switching to EBC rotors and pads. My rear lasted much longer than the front. I replaced them with Galfer. Both have been great since.

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    Anyone know where to source the bobbins? I’m looking at the parts diagrams and they just show the screws, I’m assuming the 5 dollar screws include this stuff? Confusing. I’d just like to source the washers and all that, reuse the screws...

    The diagram actually looks like the rotor has the bobbins in it....there has to be a way to get these separate.
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  9. #5
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    Fudge, just talked to the parts department, apparently the sleeves and washers come as part of the rotor, that’s crapola.
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    you can buy them from Motorworks BMW UK separately. I've just ordered a whole new brake set up form them.

    bobbins
    washers
    bolts
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, Spotlights, 50K Miles†

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    I'd check the wheel where the mounting bolt fasten, the surfaces should be free from burs and bumps. Then I'd check they are true with a DTI (dial test indicator) clock. Not sure what the official spec is but from experience it needs to be under 5 thou. you may have more leeway with floating discs.
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    Quote Originally Posted by DJ123 View Post
    you can buy them from Motorworks BMW UK separately. I've just ordered a whole new brake set up form them.

    bobbins
    washers
    bolts
    I just found this site, what a cost to get all these, sheesh.

    I’ll have to look into one of them DTI thingys.
    I’ve thought about, how could I get them ground down, evened out but I don’t know if that’s worth it either. Crud.
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    Quote Originally Posted by Superduper View Post
    I just found this site, what a cost to get all these, sheesh.

    I’ll have to look into one of them DTI thingys.
    I’ve thought about, how could I get them ground down, evened out but I don’t know if that’s worth it either. Crud.
    Yeah, they're not cheap unfortunately. But it is cheaper than buying a new set of discs rather than warping them.
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    The floating nature of this rotor design goes a long way toward minimizing vibration from a "warped" rotor - think potato chip - as long as the little mounting bobbins are free to do their thing. What they cannot do is compensate for a rotor that is of uneven thickness. This can happen when a hot rotor is partially cooled by a splash of water causing it to re-temper unevenly but not necessarily warp. Ultimately that spot may wear at a different rate causing a thicker or thinner segment on the disc.

    There are probably many other causes for this condition but the bottom line is since it is impractical to machine these very thin rotors, the only solution is to replace them with new. Try measuring your used rotors for even thickness and I'll wager that they aren't.

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    Hmm... I understand the theory, of the cool water hitting a hot rotor, but I'm not sure how that would warp the rotor in real life.

    I live in Seattle and ride in cold rain. My rotors haven't warped.

    Just puzzled, that's all.
    Elnathan - 2014 BMW F800GT
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    Quote Originally Posted by bolter1100 View Post
    The floating nature of this rotor design goes a long way toward minimizing vibration from a "warped" rotor - think potato chip - as long as the little mounting bobbins are free to do their thing. What they cannot do is compensate for a rotor that is of uneven thickness. This can happen when a hot rotor is partially cooled by a splash of water causing it to re-temper unevenly but not necessarily warp. Ultimately that spot may wear at a different rate causing a thicker or thinner segment on the disc.

    There are probably many other causes for this condition but the bottom line is since it is impractical to machine these very thin rotors, the only solution is to replace them with new. Try measuring your used rotors for even thickness and I'll wager that they aren't.

    Min service thickness is 4mm, new ones are 5mm IIRC.

    Sitting on the front brake to hold the bike after lots of braking/heat build up can cause some warping as you're creating a localised hot area and are also applying pressure. On the road you wouldn't get enough heat to get the metal up to a heat where a splash of cold water will cause it to temper.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, Spotlights, 50K Miles†

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  20. #13
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    That makes more sense. Thanks.

    Chris
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  21. #14
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    Well shoot, I just got another set of used rotors with the mounting hardware. Used, but I’m gonna give these a go.
    This guy offers 30 days return so that makes me feel better. These don’t work I’m getting new ones, ebc or whatever.
    Gonna clean the rim off good again, clean everything spotless, torque to 17lbs or whatever it is, hope for the best.

    On my original bike in 09 I think I swapped the rotors with some used ones I found on Craigslist, I was at like 60 or 70,000 miles, saw them online said let me change them, they are cheap enough. Used the same hardware, put them on, no issues.

    That’s why I wonder if there could be something else going on with my bike, bent rim or something odd that would cause that warp feel at that one spot in rotation. Guess I’ll see once I get these new used ones in.
    Quote Originally Posted by batamali View Post
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  22. #15
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    Make sure to use thread locker. Careful, I've found that the listed torque isn't always perfect for these. Variables like how clean the threads are, how much (and type) of thread locker, temperature, etc can influence it. The key in this case is to have the wavey washer half way compressed. Sometimes that doesn't take much torque (hence the importance threadlocker). After installation you should be able to wiggle them with your hand. I also found that a couple 2x4's are perfect to support the tires as a solid base with the wheel on its side.

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    Quote Originally Posted by DJ123 View Post
    Min service thickness is 4mm, new ones are 5mm IIRC.

    Sitting on the front brake to hold the bike after lots of braking/heat build up can cause some warping as you're creating a localised hot area and are also applying pressure. On the road you wouldn't get enough heat to get the metal up to a heat where a splash of cold water will cause it to temper.
    I agree that under "normal" road riding conditions your brakes would not likely get hot enough to re-temper if splashed with water but if you were riding aggressively in the twisties they definitely would. Case in point, I'm sure you have seen pictures/videos of race cars with rotors hot enough to glow.

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    In a hot country like California and you were being very aggressive, possibly yes. Real world conditions, no.

    Race car brakes are designed to work with temperature in them . . . . . with no temperature they don't work.
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    Quote Originally Posted by Superduper View Post
    So I got this used bike, rotors were warped, got some used rotors, swapped, seems that the right side is still warped slightly, noticeable. Just got another used set of rotors, one is obviously warped, the other seems good, on glass, put it on the bike, still slightly warped, not as bad as the previous but there none the less.

    Itís a gamble getting used, I know, but rotors are pricey, so Iím taking my chance, Iím a gambler.

    When I take the calipers off, Iím mounting a pencil, file, whatever, through one of the caliper bolt holes and spinning the wheel, looking for a rub or a gap, left side looks fine, right side has the slight warp. You can see a slight gap between the pencil point and the rotor at a certain point of the rotation.

    Iím wondering what could cause this?
    Iím assuming all these rotors are warped as Iím getting them, and not GETTING warped once I put them on.

    BUT, Could something about the rim be causing this? The mounting bolts and parts some how have something to do with it? Wheel bearings? something? I havenít ridden hard enough for heat to build. And I donít hold the brakes on at stops.

    I figure it canít be an unbalanced tire, canít be the master cylinder or calipers or bearings, because itís clearly at one point in the wheels rotation, while on the brakes. feeling slows when the bike slows, etc.

    The warp on the latest rotor I put on is felt more at slower speed, but is not as bad as the previous which was felt always on the brakes, and would cause the springs to bounce some pulling up to stops. Latest rotor you can feel it, but it doesnít do the spring diving thing, which is better, but still.....

    Iím just wondering if thereís things I can look for or should think about checking that I havenít already?

    I know I should get all new hardware, and donít get used rotors and all that jazz but, shoot...

    Sounds like my experience...except i keep replacing my discs with new ones.

    Was OK on the original rotors for about 25k, since then i have had to replace the rotors three times due to warping. I've had Brembo and EBC rotors, new pads, new bolts, new washers and all sorts. All been fitted by a local mechanic.
    About to get yet another set of rotors as the current ones won't pass the MOT. Will replace the wavy washers...again.

  27. #19
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    are you checking the discs for run out? That would tell you if it is the disc, or the mounts that are creating the warped feeling.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, Spotlights, 50K Miles†

  28. #20
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    Wow, I sure hope I don’t have to keep replacing rotors.
    I was thinking that maybe they are GETTING warped on the bike, but I don’t know how that could be.
    I ended up switching to organic brake pads, hoping that would take some pressure off the rotors somehow...adds a cool noise when braking, and a crap squeak after sitting...oh well.

    Just got my “new” set of used rotors on Saturday, and also found a nail in my back tire, bastage.
    Checked the left side rotor again when I took the calipers off and spun the wheel, left looks good, right is warped ever so slightly, but that’s all it takes.
    Replaced the right side, used the used mounting hardware that came with the rotors, they all came from the same bike. Check for truth when I spun the wheel again, looks good, so far the last couple days, things aren’t bobbing around coming to a stop, fingers crossed that the issue is over.
    Now I just have to get it out of my head to expect the jerking that I’d get coming to a stop.
    Now if I could only get some kinda money back for these 3 warped rotors I have laying around.
    Not gonna be an asshole and put on eBay as “good working order” lol, crooks.
    Quote Originally Posted by batamali View Post
    Can you pass that $#it you,ve been smokin Arles?...
    yes i can...

  29. #21
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    Quote Originally Posted by Superduper View Post
    Wow, I sure hope I don’t have to keep replacing rotors.
    I was thinking that maybe they are GETTING warped on the bike, but I don’t know how that could be.
    I ended up switching to organic brake pads, hoping that would take some pressure off the rotors somehow...adds a cool noise when braking, and a crap squeak after sitting...oh well.

    Just got my “new” set of used rotors on Saturday, and also found a nail in my back tire, bastage.
    Checked the left side rotor again when I took the calipers off and spun the wheel, left looks good, right is warped ever so slightly, but that’s all it takes.
    Replaced the right side, used the used mounting hardware that came with the rotors, they all came from the same bike. Check for truth when I spun the wheel again, looks good, so far the last couple days, things aren’t bobbing around coming to a stop, fingers crossed that the issue is over.
    Now I just have to get it out of my head to expect the jerking that I’d get coming to a stop.
    Now if I could only get some kinda money back for these 3 warped rotors I have laying around.
    Not gonna be an asshole and put on eBay as “good working order” lol, crooks.
    BMW recommend using Organic pads, and not sintered. I've not had any issues using organic pads, or felt I've wanted any more braking performance.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, Spotlights, 50K Miles†

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