27" to 700C with cantilevers

Discussion in 'Cycling Equipment' started by myk, Apr 1, 2009.

  1. myk

    myk New Member

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    I have an old 80s touring bike with 27" wheels, and would like to put some 700C s on. The problem of course is that the brakes need to be 4mm lower. Searching the archives, all the conversion talk seems to apply to calliper brakes, but this bike has cantilevers. The old centre-pull style, not Vs.
    The pivot point on the forks where the brake arms attach (whats it called?) is already close to the height of the pads ("shoes" to Americans, I believe). I don't have the welding skills or gear to move it lower. I figure I could file/drill the dropouts in the front forks to raise the axle 4mm. But the rear wheel is trickier, as it has a horizontal dropout.

    I wouldn't mind replacing the brakes with modern V-brakes, but that would not work well with the drop-bar brake levers, would it?

    edit: I must have made a typo searching. Now found a few relevant posts, and they talk about brakes with enough adjustment. But my problem is that the pivots are too high, so that the pads will come at the rim from the wrong angle, and hit the tyre. Its it feasible to use clamp-on (not welded) mount/pivot points for the rear canti brakes?

    Nobody mentioned the idea of modifying the dropouts.
    I know I'll need to be wary of the pedals coming closer to the ground on corners.
     
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  2. alfeng

    alfeng Well-Known Member

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    If you look at SOME-if-not-most cantilever brake calipers, the pads are on rods which can be pivoted DOWNWARD or UPWARD as need be in their gimble-like mechanism (for want of a better description) ... so, I think you may be able to simple make the 4mm adjustment after you loosen the "rods" ...

    If your calipers can't be pivoted downward/upward, then check your LBS or the mail-order outlet of your preference or eBay for a different set of calipers -- I think all of the sets of cantilevers calipers (either Shimano & Tektro) which I have can make that adjustment. I would think a USED pair in good condition (i.e., with good pads) should cost less than $20. Of course, you could pay a lot MORE if you get a fancy-schmancy set that CX racers use.

    BTW. There is something positive to be said about 27" wheels & tyres ... the equivalent size for a 27x1.25 is 700x32, so that's not a bad thing if you're riding on rougher pavement or carrying a load.
     
  3. garage sale GT

    garage sale GT New Member

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    I hope you do NOT file your dropouts. I haven't seen your bike but I serioiusly doubt you can carve away 4mm and still have a safe bike. :eek: :eek: :eek:

    Why do you want to upgrade? Those 36 spoke 27's are pretty strong if kept tensioned and trued. You could buy stronger double wall rims like Sun CR-18s (or stock replacements new or ebay). The only thing they don't have in 27 is an aero profile.

    Do you have a steel frame? You may not be able to go to a modern wheelset if you have an aluminum frame which is 126mm between the rear dropouts.
     
  4. Peter@vecchios

    [email protected] New Member

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    Canti posts on the seatstays and fork, one on each side? Or central mount in the fork crown and rear brake bridge? For center pull brakes?

    Like these?

    http://www.jitensha.com/eng/rearfndr_e.html

    http://www.jitensha.com/eng/frfendr_e.html

    Then I think you are out of luck BUT nice 27 inch rims and tires are available.
     
  5. myk

    myk New Member

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    Thanks for the replies. I think I should have shown some photos.

    Here is the front fork dropout:
    [​IMG]

    Reasonable to try filing it a little deeper?
    And here are the front brakes:
    [​IMG]

    Gee, that looks awfully rusted. The rest of the bike looks better.
    I can try moving the arms outward, and the brake pads down. I worry that the pivot points are too high though.

    Yes, it it steel (CrMo), so I could widen the rear, though that was not the plan.
    This is motivated by the original rear wheel being badly bent,
    and I have some old 700C wheels and tyres lying around.
     
  6. alfeng

    alfeng Well-Known Member

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    IMO, I think you will be good-to-go if you simply adjust the angle of the pad holders ...

    Because, when I changed my Gitane from 27" wheels to tubulars, I simply adjusted the MAFAC center-pull calipers (similar brake pad attachment) in the manner which I previously suggested AND it looks like there IS sufficient wiggle-room for you to do the same.

    FYI. As far as filing away some material, while you CAN certainly make minor adjustments (~1mm) to the dropouts, YOU shouldn't because
    • You don't have to, and
    • It will probably take a great deal of patience for a non-framebuilder -- the manual skill level is actually low if you are handy BUT you have to have a good eye to ensure that the wheel sits squarely in the fork and/or frame after you are done ... otherwise, the wheel won't sit squarely in the fork-or-frame and could cause handling problems.
    This is certainly something that framebuilders did if things weren't perfectly aligned.
     
  7. garage sale GT

    garage sale GT New Member

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    Can you mount the pads so that the rubber is further away from the attachment to the pivoted cantilever arm? Then you'd have to splay the arms out wider to fit the pads around the rim, and since they rotate about the pivot the pads might end up a lot lower.

    I feel if you modify the dropouts, then you're on crack, or soon will be. :D (well, maybe ~1mm would be safe.)
     
  8. myk

    myk New Member

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    OK, no filing then. I'll give it a try with the existing brakes and see how they go. Thanks!
     
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