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  1. #1
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    Reputation: wddamf's Avatar
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    Juicy 7 gobble source theory

    After ditching my J7 because of the constant gobble (see my other post for all that I did to try to solve it), I installed new Formula K24's using the Avid adapters. After mounting the K24's, I noticed they were slightly our of square relative to the rotor and they didn't seem perfectly tight and secure. I then noticed that the faces of the Avid adapters were far from flat and/or square. Avid probably doesn't worry about this figuring the CPS washers would take care of any out-of-square'ness of the adapters. The turkey gobble is because of vibration - components will vibrate "more" when loose - these adapters with "non-flat" mounting faces will allow the calipers to vibrate more than if the adapter faces were flat and square. I wonder if this might not be one source of the trukey gobble.

    I rigged up a jig on my table saw table. Using a file, some clamps, a framing square, and several blocks, I flattened and squared the faces of the adapters. The K24's are now square to the rotors and they seem to have a more secure mouting after "fixing" the adapters. And they are perfectly quiet.

    Would this have solved the J7's gobble? Maybe. Am I going to reinstall them to find out? Nope! BUT if anybody else out there is fighting the dreaded gobble, try some mounting adapters from a different manufacturer (one that faces the mounting surfaces) and see if that doesn't fix / improve the situation.

  2. #2
    Meh.
    Reputation: XSL_WiLL's Avatar
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    Hmmm... I have one Avid adapter right now, and I just checked, it's pretty flat. But good catch, that definitely may have been an issue. It may be possible that manufacturing tolerances for the adapter aren't as tight because they figure the CPS will compensate for it.

  3. #3
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    My adapters were painted raw castings - no machining on the mounting faces at all. When I started filing the faces in my home-grown jig, it became very obvious how "un-flat" they were based on where the paint was being removed!

    I'm surprised Avid didn't figure this out (IF it's the source of the problem) - sure would have been a cheap solution for warranty claims.

  4. #4
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    Reputation: Jerk_Chicken's Avatar
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    I noted this about the rough castings as well. I've had success by using different adapters, as have some others.

    They now exist in a box and work perfectly there.

  5. #5
    Dat mah bike, punk!
    Reputation: misctwo's Avatar
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    Quote Originally Posted by Jerk_Chicken
    I noted this about the rough castings as well. I've had success by using different adapters, as have some others.

    They now exist in a box and work perfectly there.

    i just had a look at the formula K24 adapters and they look like they've been machined flat and square. but my K24's DO have a strange 'turkey gobble-like' sound to them when i'm clamping hard. i thought it was more from the braking energy being 'stored' in the spokes of the wheel, winding up, rubbing, and being released. might be a silly thought? Will, what do you think?

    another possiblity is that the rotor simply gets hot and expands differntly at each section?
    Last edited by misctwo; 03-09-2007 at 07:00 PM.
    every thread needs an uploaded image of one kind or another.

  6. #6
    Meh.
    Reputation: XSL_WiLL's Avatar
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    Hot spotting? Maybe the rotor isn't a constant thickness? Maybe the rotor doesn't have a constant surface area?

    The spokes and reasonance and all that are plausible. I suppose you can test that by putting something between the spokes like a piece of cloth or something.

  7. #7
    Dat mah bike, punk!
    Reputation: misctwo's Avatar
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    Quote Originally Posted by XSL_WiLL
    Hot spotting? Maybe the rotor isn't a constant thickness? Maybe the rotor doesn't have a constant surface area?

    The spokes and reasonance and all that are plausible. I suppose you can test that by putting something between the spokes like a piece of cloth or something.

    i dunno, but they were a constant thickness when they started out...and the stock formula rotors have a slight mudcutter profile.


    might get some galfer rotors.
    every thread needs an uploaded image of one kind or another.

  8. #8
    Anytime. Anywhere.
    Reputation: Travis Bickle's Avatar
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    It feels to me that the rotors weren't of an even thickness. I had an old Syncros rim that wasn't en even thickness and it felt similar. It think this at least part of it. I have round rotors now and everything is fine.
    I got some bad ideas in my head.

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