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  1. #1
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    Code 5 Endless Humming!!!

    My rear brake is humming so bad that after a few hours on the trail it loosens the rear axel (it's been tight).
    I've resurfaced both rotors, with fine grit sand paper and scotch brite pads, tried new brake pads after resurfacing old ones, swapped out back rotor for the front rotor (back still hummed while front didn't.), cleaning thoroughly with isopropyl alcohol before, durring and after each "trial".

    Set up:
    Brakes: Avid Code 5 8" rotors (stock rotors)
    Frame: On One 456 Summer season
    Hub: Transition Revolution rear with 15" quick release axel



    What else could it be?? Could the rotor have to many vents so the pad gets caught up in them? Rear axel loosening? Could the vibrations from the humming cause that, or does that sound like a totally different issue? Does it have to do with the frame and brake combo (the resonance of the 8" rotors is harmonizing with the frame somehow (maybe I'm thinking too much...)?
    Ride your bike and be happy.

  2. #2
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    Unfortunately what you're experiencing with the vibration is a very common problem with Code 5's, however in your case I wonder if having such a large rotor makes things worse. I experienced the same problem on my XTC 29er1. Once you apply a strong braking force to the rear brake the whole bike starts vibrating.

    Essentially the Code 5 rotor sucks,it's a one piece unit that's mounted directed to the wheel. Not only that but it's prone to flex under high loads so the harder you stop the more intense that vibration becomes.

    I got around my problem by going to a Shimano RT-76 rotors on my XTC 29er. The RT-76 is a two piece rotor partially insulating the rotor from braking forces. On an RT-76 rotor the section that is attached to your frame is different from the part where braking forces are applied. Unfortunately the bicycle shop had to chop off the part of the brake pad to make the new rotors fit but most of my vibration problems went away. I still get some slight vibration in the begining of braking but after the calipers start gripping the vibration goes away.

  3. #3
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    Would any two piece rotor do the trick?

    I'll probably drop to a 160mm rotor in the back as well...
    Ride your bike and be happy.

  4. #4
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    I'll bet your pistons are not moving in unison. Remove the wheel and see if all four pistons move in and retract at the same speed. If even one piston is sticky, it'll cause problems.

  5. #5
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    Would any two piece rotor do the trick?

    Unfortunately I haven't tried the Hayes or Avid two piece rotors. There are two reviews for the Avid XX rotor one is favorable and other less so. The Prime Pro rotors look nice but I haven't tried them.

    Aside from getting rid of your vibration the RT-76 rotors will increase your braking power as well. Even though I only have a 160mm rotor on the back of the XTC 29er1 the rear brake generates quite a bit of power and it's very easy lock it up.

  6. #6
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    I'll take a look at the pistons.

    Would a video of it help? I'm sure there are different types of vibrations/squeaks/squeals/hums... If you could hear it it might rule some things out.
    Ride your bike and be happy.

  7. #7
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    Long answer:
    I have some experience of this; what you are experiencing certainly sounds like frame resonance. The rear triangle is rigid, but the steel tubing can still resonate, causing the shudder. If the natural (structural) resonant frequency of the frame is close enough to that generated by the brakes, what is known as a positive feedback loop can occur, leading to significant amplification of the vibration. In essence, the vibration of the frame and the brake match, leading to constructive interference. The front end of the bike is likely better damped and therefore absorbs more of the vibration generated by the brake. The resonant frequency should also be lower (higher oscillating mass). This is why swapping f/r rotors doesn't change much. To get rid of the vibration, you want to either eliminate the origin of the vibration and/or move the frequency of the vibration out of the resonant band of the frame. Changing the brake disc should accomplish this.

    Short answer:
    G2 and G3 Avid brake discs are prone to vibration, you might want to try other brand discs before going any further. Personally I like Hope and Formula's 2-piece alu-carrier discs. Very bling.
    Last edited by anlin; 03-10-2012 at 08:35 AM.

  8. #8
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    Quote Originally Posted by BikeAdvocate View Post
    I'll take a look at the pistons.

    Would a video of it help? I'm sure there are different types of vibrations/squeaks/squeals/hums... If you could hear it it might rule some things out.
    With the Code5s I had, the uneven piston movement would cause the leading edge of the pad to contact the rotor first. The opposite of what you want. Think about how you are s'pose to toe-in rim brakes. Well, the opposite was happening and I had loud squealing. I'm pretty sure this is your problem.

  9. #9
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    Quote Originally Posted by anlin View Post
    Long answer:
    ...The rear triangle is rigid, but the steel tubing can still resonate, causing the shudder. If the natural (structural) resonant frequency of the frame is close enough to that generated by the brakes, what is known as a positive feedback loop can occur, leading to significant amplification of the vibration. In essence, the vibration of the frame and the brake match, leading to constructive interference...
    I thought I was crazy for thinking this. Thank you for your input and the way you wrote it. It's a pretty intense vibration, that's the only reason I thought it could be more than a contaminated pad or something similar.

    Those Hope rotors do have a pretty sweet bling factor.

    I'll still take a look at the pistons today to see if the travel is getting hung up in any way that would cause the leading edge of the pad to contact first.
    Ride your bike and be happy.

  10. #10
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    Here's a pic of the caliper and pads so you can see the pistons. This is right after taking the pads off.


    As you can see the right front is set in further than the right rear piston. The left are even though.

    The pads resemble how the pistons are set:
    Front is oriented <----- that way and top pad is the right, bottom is the right.
    Ride your bike and be happy.

  11. #11
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    I would "clean" those brake pistons. Some lubricate them with brake fluid or rubber grease some say don't lubricate them just clean them.

    I squeezed the lever to advance the pistons. Then cleaned them with brake cleaner and a q tip. I used rubber grease to lubricate my pistons.

    From the Avid manual
    ‘sticky’ or slow brake pad return feel
    Before completely disassembling your
    caliper, it’s worth trying to loosen the sticky
    piston. Try the following: Clamp bicycle in
    bicycle work stand. Spin affected wheel.
    Lightly squeeze brake lever and watch brake
    pads when lever is released. Determine
    which side of the caliper has a slow returning
    brake piston. Remove caliper from
    bicycle. If you have a mounting bracket, it
    is recommended to remove that too or just
    remove the caliper leaving the bracket on
    the fork or frame. Using a pair of needlenosed
    pliers, remove both brake pads and
    h-spring. Using an 11mm box wrench, press
    working piston into caliper body. Squeeze
    brake lever slowly to move sticky piston inward.
    Press the piston back into the caliper
    again. Repeat these steps to correct caliper
    piston inner o-ring position. Both pistons
    should now be moving freely. Re-install
    h-spring and pads into caliper. Re-install
    caliper onto bicycle. Spin wheel and check
    function. If there is no improvement, continue
    with caliper service.
    Duct tape iz like teh Force. It has a Lite side and a Dark side and it holdz the Universe together.

  12. #12
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    Quote Originally Posted by mitzikatzi View Post
    I would "clean" those brake pistons. Some lubricate them with brake fluid or rubber grease some say don't lubricate them just clean them.

    I squeezed the lever to advance the pistons. Then cleaned them with brake cleaner and a q tip. I used rubber grease to lubricate my pistons.
    Yeah, I push the pistons out and clean them w/ a Qtip too.

    I've been lubing them w/ a little bit of 3-in-1 oil. Hmmm,I hope the seals are ok w/ 3-in-1 oil.

  13. #13
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    Oil can make some rubber seals swell.

    I remember working on a cars rear drum brakes with poor rear axle seals (oil leaks). The rubbers in the brake cylinders where very swollen.

    Some say it is ok to use oil on your brake pistons. I think I read in an Avid manual (or maybe elsewhere). It states not to use oil.

    This is for brakes that use DOT fluid.

    I have also used denatured alcohol and a toothbrush to clean brake calipers.
    Last edited by mitzikatzi; 03-10-2012 at 05:21 PM.
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  14. #14
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    Thanks. No more oil in there for me. Just in case.

  15. #15
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    It is paramount the right kind of lubricant is used, as using non-compatible products can cause the seals to deteriorate, just as mitzikatzi mentioned. Personally, I use q-tips and 99% isopropyl (rubbing) alcohol (safe to use on both DOT and mineral oil systems) to clean the muck off the pistons, then either some brake fluid or red rubber grease to make things run smooth.

  16. #16
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    Yeah, my calipers are pretty gnarly. I'll use some isopropyl and Q'tips to de-sludge. I'm assuming I can use DOT 3 fluid then on the pistons or does it have to be DOT 5?

    I'll see if that helps with some of the noise/vibration as well.
    Ride your bike and be happy.

  17. #17
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    Do NOT use DOT5 for any purpose on your brakes! DOT5 is silicone based and will destroy your seals. Not sure about DOT3, but DOT4 and 5.1 should be fine.

  18. #18
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    DOT 3, 4, and 5.1 fluids are glycol based while 5 is silicone based for it's higher temperature rating.

    So are all but 5 fine to use on the pistons?
    Ride your bike and be happy.

  19. #19
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    To "lube" the piston 3, 4 and 5.1 are ok to use.

    If you plan on changing the fluid in your brakes ie flush and bleed. To get the very best from your bike use 5.1.
    4 will be OK.
    3 has a lower boiling point.
    Due to the small volume of brake fluid used it can get hot. So best to use 4 or 5.1.
    Duct tape iz like teh Force. It has a Lite side and a Dark side and it holdz the Universe together.

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