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Thread: Frame flex

  1. #1
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    Frame flex

    Post number 1 and I come here to complain...............

    I have a 2011 Trance X2 and cannot get the rear brake to operate without a loud whining sound. The sound is pretty much constant which to me indicates the rotor is straight and is loud enough to make dogs bark and mothers cover their childrens ears as I approach. My riding buddy has told me to fix it or else I'll be riding on my own.

    I have tried to realign the calipers, clean the pads, new pads, resurface the pads. The brakes are bled correctly (unless the LBS doesn't know what they are doing of course) and the wheel spins freely and without noise until I sit on the bike.

    The LBS have even put a new caliper on the back to try that out.

    The only thing left that I can think of is that the frame is flexing when I sit on the bike, just enough to bring the pad on one side into contact with the rotor. It's the outside pad so that would fit.

    Now I've read everything I can about the Avid Elixir 5's and realise they aren't without problems but this seems to be beyond that. The other thing I've noticed is that the rotor will not centre fully and the washer things holding the caliper on the post mount are at their limit. Does this mean the post mount points are out of tolerence?

    Has anyone heard of problems with frame flex? It is an XL frame and I weigh 105kg (230lbs) and am 6'8".

  2. #2
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    Have you tried sitting on the bike while your LBS realign your caliper?

  3. #3
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    That's tonight's task. I'll give it a crack and see what it looks like.

  4. #4
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    what about the rear hub? any play in the bearings?

  5. #5
    Tool
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    It's possible that your entire rotor is bent outboard (I beleive you said it was the outboard pad that rubs).

    It's very easy to push the entire rotor back inward. This will allow you to get the caliper properly centered. This, of course, assumes your hub bearings are in check as mentioned above, and that the wheel is properly mounted with the skewer tight.

    I had this happen to me before. I actually thought it was my shock making the noise as I'd get a slight honk with each pedal stroke only under certain conditions, and never with pro-pedal turned on. The problem was getting worse during one ride, and then I took a slow u-turn on a slope - the brake made noise throughout the turn and brought my attention to it. My first attempt was to align the caliper, but I noticed it couldn't move far enough to be centered. Next was to tweak the rotor, after which all was well.

    Good luck,
    Pete
    I can barely get my mouth around it.

  6. #6
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    Sorry to hear this (yet again)....my recommendation is to get rid of the Avid brakes and go for something not so temporamental like Shimano or Magura.
    ...and proud member of the anti-sock puppet desolation

  7. #7
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    see this: How to eliminate resonant frequency in AL frame? Expanding foam? Lead weights?
    your problem may not have anything to do with brake adjusting, it could be that your particular frame resonates with your particular brake (your frame's natural frequency is the same or a multiple of the brake's vibrating frequency). the above thread addresses this.

  8. #8
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    So after a whole lot of messing about I think I might have a fix. In short, the method for aligning the caliper that Avid (and almost everywhere else) give of loosening off the bolts and pumping the brakes a few times before holding the brake hard on and doing up the bolts again isn't enough to get significant movement in the washers on the mounting bolts. I did test last night of loosening off the bolts and pushing the caliper hard away from the wheel before holding the brake in hard and tightening the bolts. In doing this I managed to get the pads on the inside to rub on the rotor.

    So the next step was to hold the caliper with the rotor centred as best I could and then tighten the bolts while holding the brake on. It seems quite simple but that's all it took and results in a hugely different outcome to the Avid method.

  9. #9
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    Quote Originally Posted by cep32
    So after a whole lot of messing about I think I might have a fix. In short, the method for aligning the caliper that Avid (and almost everywhere else) give of loosening off the bolts and pumping the brakes a few times before holding the brake hard on and doing up the bolts again isn't enough to get significant movement in the washers on the mounting bolts. I did test last night of loosening off the bolts and pushing the caliper hard away from the wheel before holding the brake in hard and tightening the bolts. In doing this I managed to get the pads on the inside to rub on the rotor.

    So the next step was to hold the caliper with the rotor centred as best I could and then tighten the bolts while holding the brake on. It seems quite simple but that's all it took and results in a hugely different outcome to the Avid method.
    I've found getting it right is a mix of science and art.

    The main problem with the simple squeeze and tighten method is friction between the bolt and caliper can easily move the caliper out of position while torquing the bolts. I've gotten the best results by examining the current position of the caliper over the rotor before loosening the caliper, giving the lever a few squeezes as you observe - it's not unusual for a caliper to look centered only to find it pushes the rotor to one side when the pads engage. A little awareness can go a long way.

    Sometimes when the caliper is being fussy and seems to want to settle too far inboard or outboard, purposely positioning it too far in the other direction and fully tightening it can allow you to get it to just the right spot if you follow up with the Avid squeeze and tighten method.

    Since friction is a large part of the problem, it does help to makes sure all mounting hardware is clean and minimally lubed (you obviously need to be very careful with lube in this area - apply the lube to clean hardware away from the bike, wiping off all excess with a clean rag). Also, when a caliper is being fussy, I like to loosen the bolts enough to be able to freely rotate the mounting hardware; this reduces the chances of binding while tightening.

    -Pete
    I can barely get my mouth around it.

  10. #10
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    Thanks for the tips everyone. I put a little grease on the bolts last night and had a bit more of a play. Managed to get the rotor almost bang on centre and it has stayed there under heavy braking. The tendancy for the rotor to end up resting on the outer pad seems to be not helped by the caliper sagging to the inside of the frame due to its weight being on that side of the mount. A little bit of a hand to centre seems to go a long way.

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