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  1. #1
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    Disc brake problem

    I am having an odd problem with my front disc brake calipers, or possibly it is a wheel/rotor problem.

    The bike is a new Cervelo R3 with the RAT thru axle. The wheels are generic carbon wheels with Formula hubs and Dura Ace rotors.

    After the rotor and calipers are aligned, the rotor after a while starts to lean over slightly to the left side of the bike, just enough to contact the brake pad. There are two ways of correcting this: the first is to loosen the thru axle, angle the wheel slightly to the right and re-tighten. This works fine for about an hour or two, and then the rotor starts to lean to the left again.

    The other way of correcting it is to adjust the calipers around the rotor without adjusting the wheel. This also works fine for an hour or two, and then the same thing happens - the rotor leans to the left and makes contact with the brake pad.

    In other words, adjusting either the wheel or the calipers produces exactly the same result, with the rotor moving to the left and touching the brake pad.

    I have had it adjusted by the best local mechanic, with the same result.

    Any suggestions on how to fix this? Does this sound like a wheel or rotor issue? An issue with the fork? The calipers? It is driving me nuts.

  2. #2
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    Quote Originally Posted by rossb View Post
    I am having an odd problem with my front disc brake calipers, or possibly it is a wheel/rotor problem.

    The bike is a new Cervelo R3 with the RAT thru axle. The wheels are generic carbon wheels with Formula hubs and Dura Ace rotors.

    After the rotor and calipers are aligned, the rotor after a while starts to lean over slightly to the left side of the bike, just enough to contact the brake pad. There are two ways of correcting this: the first is to loosen the thru axle, angle the wheel slightly to the right and re-tighten. This works fine for about an hour or two, and then the rotor starts to lean to the left again.

    The other way of correcting it is to adjust the calipers around the rotor without adjusting the wheel. This also works fine for an hour or two, and then the same thing happens - the rotor leans to the left and makes contact with the brake pad.

    In other words, adjusting either the wheel or the calipers produces exactly the same result, with the rotor moving to the left and touching the brake pad.

    I have had it adjusted by the best local mechanic, with the same result.

    Any suggestions on how to fix this? Does this sound like a wheel or rotor issue? An issue with the fork? The calipers? It is driving me nuts.
    Perhaps the pad is moving instead of the rotor. Seems more likely

  3. #3
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    This sounds like a rotor warping issue when hot, does the amount of brake use affect how quickly this behavior occurs? Any chance the rotor can be swapped out with another?

  4. #4
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    CALIPER...singular. There is ONE at the front, and ONE at the rear.

    If your thru axle is adjusted to be as tight as it should you're not doing what you think you're doing. There is no way you're 'angling the wheel slightly to the right'. Can't happen. It's always going to be in the same place. If the rotor moves after you make an adjustment it's not tight enough.
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  5. #5
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    Thanks for the responses.

    Quote Originally Posted by deadleg View Post
    Perhaps the pad is moving instead of the rotor. Seems more likely
    I thought that might be a possibility as well, but it happens even when the bike is left in the garage overnight and the pad isn't used.

    Quote Originally Posted by nova_rider View Post
    This sounds like a rotor warping issue when hot, does the amount of brake use affect how quickly this behavior occurs? Any chance the rotor can be swapped out with another?
    See comment above - I can set the bike up with the rotor aligned perfectly in the caliper the night before the ride, but by the morning it has again drifted left. I don't have another rotor but might try a different one to see if this improves things.

    Quote Originally Posted by cxwrench View Post
    If your thru axle is adjusted to be as tight as it should you're not doing what you think you're doing. There is no way you're 'angling the wheel slightly to the right'. Can't happen. It's always going to be in the same place. If the rotor moves after you make an adjustment it's not tight enough.
    I'll check this again and try tightening it further, although I was closing it about as tight as I could (at least as tight as I do with rim brake quick releases). Perhaps the problem is the thru axle has the open cam type of closing mechanism, which may loosen a bit over time. I might see if there is an alternative thru axle with a better cam design.

  6. #6
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    Coming from a metallurgical standpoint, it sounds like the rotor might not have been properly annealed/ stress relieved, which will result in it warping in the same direction whenever heated. Replacing the rotor may be the only solution.
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  7. #7
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    Quote Originally Posted by deadleg View Post
    Perhaps the pad is moving instead of the rotor. Seems more likely
    This.

    Take the wheel off, removed the pads, and see if you can reseat the pistons with a piston press. Re-install, see if it happens again. If it does, repeat the piston reseat, and if it's the same piston then you've found your culprit.

    Or, I could be totally wrong. In which case, apologies in advance.

  8. #8
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    I think a new bike would be a solution, 100% guaranteed!
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  9. #9
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    first of all, how do you go about determining that the rotor is moving? You would need to use a fixed reference point to determine this. If you're eyeballing the rotor against the brake pads, then this is NOT a reliable way to check if the rotor is warped or not. You could use a long ziptie and strap it to the fork leg and use the ziptie to check on the rotor (like how you would true a wheel).

    My hunch tells me that you have a faulty caliper/piston. The reason it would be faulty is because it's piston is binding a bit and not releasing the pads far enough to clear the rotor after some time of usage. You might want to examine of there is any dirt/grease inside the cylinder which hold the piston. Push the piston back and clean the cylinder with rubbing alcohol.

    (on a sidenote: disc brakes related questions such as this will become more and more common. Fact of life of disc brakes).

  10. #10
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    Quote Originally Posted by aclinjury View Post
    first of all, how do you go about determining that the rotor is moving? You would need to use a fixed reference point to determine this. If you're eyeballing the rotor against the brake pads, then this is NOT a reliable way to check if the rotor is warped or not. You could use a long ziptie and strap it to the fork leg and use the ziptie to check on the rotor (like how you would true a wheel).

    My hunch tells me that you have a faulty caliper/piston. The reason it would be faulty is because it's piston is binding a bit and not releasing the pads far enough to clear the rotor after some time of usage. You might want to examine of there is any dirt/grease inside the cylinder which hold the piston. Push the piston back and clean the cylinder with rubbing alcohol.

    (on a sidenote: disc brakes related questions such as this will become more and more common. Fact of life of disc brakes).
    You can easily determine if the rotor is warped by looking at it pass between the pads, any lateral runout is very obvious. I do this every day.

    I agree w/ a possibly dirty piston. I will always clean/lubricate a piston w/ whatever the brake fluid is for that system if the brake remains on the bike and I'm not taking it apart. In the case that I remove the caliper and pistons/seals are being replaced I'll use brake cleaner.
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  11. #11
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    I don't think the problem can be caused by the rotor heating and becoming warped. As I mentioned above, the rotor will drift to the left even when the bike is not being used. So it will occur even when there is zero heating of the rotor or use of the pads/piston.

    I will check the pistons and brake pads - probably a good thing to do anyway - but I also doubt it is being caused by a dirty piston or brake pad, since the bike has had this problem literally since day one. This is why it is such a conundrum!

    But I appreciate the responses.

  12. #12
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    Are you sure you have tightened the thru axle to the proper spec? For most thru axles and wheels the torque is quite high. On my DT Swiss thru axles the spec is 15Nm.

    My guess is that you donít have a thru axle tightened and itís allowing the wheel to move, because as cx said, that should not be able to happen.
    Last edited by fronesis; 2 Weeks Ago at 10:19 AM.

  13. #13
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    It's a good point, and I will see if tightening it further will help.

  14. #14
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    Quote Originally Posted by rossb View Post
    It's a good point, and I will see if tightening it further will help.
    Grease or Anti Seize the threads of the thru axle or they'll get stuck. Ask me how I know...
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  15. #15
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    There are no threads - it is RAT axle.

  16. #16
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    Quote Originally Posted by rossb View Post
    There are no threads - it is RAT axle.
    Ah yes, that's right. Nevermind.
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  17. #17
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    So let's assume that the OP has done these:

    1. tighten skewer
    2. check that the rotor is not warped (spin the rotor and eyeball it against a fixed point to see of the rotor is wobbling)

    Then OP will "align" the wheel such that the rotor is not touching the pads. Although, I don't know how he can "align" the wheel anymore than just clamping it down. I mean this is what a thru-axle is supposed to do, take the guess work out of aligning the wheel.

    Then after some time riding, OP says rotor is touching the pads. Well, the rotor are bolted to the hub and it ain't moving. So this leave the piston as the only moving part and most likely to be the culprit, IMO. What the OP needs to do here is this:
    1. "align" his wheel so that he gets no rubbing.
    2. take the wheel out and take note of the position of the pads and piston in the caliper. Pay very close attention to the piston, down to the millimeter.
    3. go for a ride and do some braking to get the rubbing to occur
    4. now check the position of the pads and piston again. If the piston and/or pads seem to be not in the position in step #2, then it's clear that the piston/pads are the faulty component. With tight tolerance of hydro disc, all it takes is for the piston to be less than 1mm closer to the rotor and the pads will rub it.

    Even new caliper can have this happen. My buddy's bike had this happened and the LBS ended up changing out his caliper on a brand new bike. So.

  18. #18
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    Quote Originally Posted by aclinjury View Post
    So let's assume that the OP has done these:

    1. tighten skewer
    2. check that the rotor is not warped (spin the rotor and eyeball it against a fixed point to see of the rotor is wobbling)

    Then OP will "align" the wheel such that the rotor is not touching the pads. Although, I don't know how he can "align" the wheel anymore than just clamping it down. I mean this is what a thru-axle is supposed to do, take the guess work out of aligning the wheel.

    Then after some time riding, OP says rotor is touching the pads. Well, the rotor are bolted to the hub and it ain't moving. So this leave the piston as the only moving part and most likely to be the culprit, IMO. What the OP needs to do here is this:
    1. "align" his wheel so that he gets no rubbing.
    2. take the wheel out and take note of the position of the pads and piston in the caliper. Pay very close attention to the piston, down to the millimeter.
    3. go for a ride and do some braking to get the rubbing to occur
    4. now check the position of the pads and piston again. If the piston and/or pads seem to be not in the position in step #2, then it's clear that the piston/pads are the faulty component. With tight tolerance of hydro disc, all it takes is for the piston to be less than 1mm closer to the rotor and the pads will rub it.

    Even new caliper can have this happen. My buddy's bike had this happened and the LBS ended up changing out his caliper on a brand new bike. So.
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  19. #19
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    Quote Originally Posted by aclinjury View Post
    So let's assume that the OP has done these:

    1. tighten skewer
    2. check that the rotor is not warped (spin the rotor and eyeball it against a fixed point to see of the rotor is wobbling)

    Then OP will "align" the wheel such that the rotor is not touching the pads. Although, I don't know how he can "align" the wheel anymore than just clamping it down. I mean this is what a thru-axle is supposed to do, take the guess work out of aligning the wheel.

    Then after some time riding, OP says rotor is touching the pads. Well, the rotor are bolted to the hub and it ain't moving. So this leave the piston as the only moving part and most likely to be the culprit, IMO. What the OP needs to do here is this:
    1. "align" his wheel so that he gets no rubbing.
    2. take the wheel out and take note of the position of the pads and piston in the caliper. Pay very close attention to the piston, down to the millimeter.
    3. go for a ride and do some braking to get the rubbing to occur
    4. now check the position of the pads and piston again. If the piston and/or pads seem to be not in the position in step #2, then it's clear that the piston/pads are the faulty component. With tight tolerance of hydro disc, all it takes is for the piston to be less than 1mm closer to the rotor and the pads will rub it.

    Even new caliper can have this happen. My buddy's bike had this happened and the LBS ended up changing out his caliper on a brand new bike. So.
    Thanks for your detailed response. A couple of comments.

    The rotor is not warped. When properly set up in the caliper it rotates freely in the center between both pads.

    But after some time the rotor will lean slightly at an angle to the left, just enough to contact the left pad. This happens whether the bike is ridden, or even if it is just left in the garage overnight.

    Since it happens even if the bike is not ridden and the brakes are not used, it seems unlikely to be a piston or brake pad issue. Unless the piston is jumping out of its own volition when no one is looking and pushing the rotor I can't see how this could happen. It would be different if it only happened after riding the bike - this would definitely suggest that one of the pistons is pushing the rotor across too far.

    Nevertheless, I will try anything at this point, so will look closely into the pistons and pads as you suggest.

  20. #20
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    I think it is the 'disk', did you try a different one?

    You state that the disk is leaning to the left...
    does that mean that the bottom (opposite side) is leaning to the right? This would be virtually impossible unless the wheel is loose.
    I think you mean the disk is dishing to the left. This would mean it is dishing, and the disk may have manufacturing stress in it or something beyond this world.

    Or maybe take it off and turn it around backwards.
    Or maybe take the wheel off and put a level or straight edge on it and see if it is dished.

    Metal pieces can move with a change in temperature, you don't want this in a disk, but in a thermostat it works great.
    Last edited by duriel; 2 Weeks Ago at 08:56 AM.
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  21. #21
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    Is it possible that temperature variations are causing the piston to move?

  22. #22
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    Quote Originally Posted by J.R. View Post
    Is it possible that temperature variations are causing the piston to move?
    Brake calipers/pistons are designed specifically to work in rather large temperature variations. They could easily experience a 100įC change while in use.

  23. #23
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    Quote Originally Posted by duriel View Post
    I think it is the 'disk', did you try a different one?

    You state that the disk is leaning to the left...
    does that mean that the bottom (opposite side) is leaning to the right? This would be virtually impossible unless the wheel is loose.
    I think you mean the disk is dishing to the left. This would mean it is dishing, and the disk may have manufacturing stress in it or something beyond this world.

    Or maybe take it off and turn it around backwards.
    Or maybe take the wheel off and put a level or straight edge on it and see if it is dished.

    Metal pieces can move with a change in temperature, you don't want this in a disk, but in a thermostat it works great.
    I haven't yet tried a different rotor (I don't have another one to hand). The rotor is not warped or dished. I think you are correct that the wheel must be loose, which is the only way the rotor can be angled like that. I have tightened down the lever and it seems to have survived in the correct position overnight, so hopefully it was just a question of tightening it to a sufficient degree - which I would previously have regarded as overtightened on a rim brake quick release.

  24. #24
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    Quote Originally Posted by rossb View Post
    I haven't yet tried a different rotor (I don't have another one to hand). The rotor is not warped or dished. I think you are correct that the wheel must be loose, which is the only way the rotor can be angled like that. I have tightened down the lever and it seems to have survived in the correct position overnight, so hopefully it was just a question of tightening it to a sufficient degree - which I would previously have regarded as overtightened on a rim brake quick release.
    well you sure have a mystery on your hand.

    At this point, I'm narrowing down your issue to
    1. the piston (as I have explained above and you need to check piston positions)

    2. the hub. It's conceivable that your hub has faulty/loose bearings that somehow would allow the entire wheel to lean to the left thus causing the rotor to lean left too. You can check your wheel/hub assembly for looseness by shaking it side-to-side. But the rotor is not leaning by itself! because the damn thing is bolted solid to the hub!

  25. #25
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    Quote Originally Posted by rossb View Post
    I have tightened down the lever and it seems to have survived in the correct position overnight, so hopefully it was just a question of tightening it to a sufficient degree - which I would previously have regarded as overtightened on a rim brake quick release.
    Having lots of experience with QR skewers on rim brake bikes, I was very surprised at how much torque was required to properly tighten a disc brake thru axle.

    DT Swiss says that if you use their handle you should tighten it as tight as you possible can Ė and this makes sense since 15Nm is well beyond "hand tight."

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