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  1. #1
    Retired dabbler hobkirk's Avatar
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    Acton, MA (20 miles west of Boston) - GORGEOUS cycling territory!
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    2007 Specialized Roubaix Elite Triple - 1st ride = century 9/19/2010 * * 2007 GT Carbon Series 2, Ultegra - 7/2010 - 2,000 miles, (replaced 'cuz it was too small) * * 1975 Lotus Odyssey - resurrected & ridden 400 miles to "try out" cycling
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    Moving Ultegra Front Derailleur from 35mm to 32mm downtube - Can I "shim" it?

    I'm swapping Ultegra parts from a GT to a Specialized Roubaix. Dumb me, I figured most downtubes would be the same diameter just for the sake of mounting FD's. Now I find there are two common sizes - 34.9 mm and 31.8 mm. ARGH! I don't want to buy a new FD.

    Is it possible to shim it?

    A rubber inner tube doesn't work - the FD squishes it under load and the whole FD twists. Obvious after I tried it.

    Is it worth trying to fabricate a metal shim (1.5 mm thick)?

    Thanks.
    2007 Specialized Roubaix, 105 Triple
    Started cycling 6/1/2010 at 64 - lethargy, bad knees, & 247# triggered my foray into cycling
    200# as of 9/9/2012 (mostly from diet, 40# in 5 mo)
    2010 (1st 7 mo) = 4.7K miles (a little nuts), 2011 = 6K

  2. #2
    Senior Member mechBgon's Avatar
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    Shims will work. In fact, your LBS may have some commercially-made shims for that purpose. The metal pieces from a set like this would do the job (do NOT overtorque the clamp bolt on your Roubaix, however): http://www.jensonusa.com/store/produ...leur+Shim.aspx

  3. #3
    Senior Member
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    I have a folded playing card shimming the front derailleur on my latest build (A magic the gathering card, can't vouch for any other type of playing card )

    The derailleur is 31.8, the tube is 28.-something. It is on my to-do list to buy a real shim for it, but because this is one of those parts whose markup is ***tarded ($4 for 2 cents worth of aluminum, plus another $4 for shipping) I'm just waiting to find a cheap set. With a bit of luck one of these days I'll buy something at a LBS and they will let me have a used shim for a buck or two.

  4. #4
    cab horn
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    1987 Bianchi Campione
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    I shimmed a 31.8 derailleur clamp to 28.6 when I bought the wrong size years ago, with a couple layers of a heneiken can. Worked great. Looked hack as **** though.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  5. #5
    Constant tinkerer FastJake's Avatar
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    You can shim with anything as long as it holds and doesn't F up your paint (if you care about that.)

    By the way, I think you mean seat tube A FD on a downtube would be quite the sight.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

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