Advertise on Bikeforums.net



User Tag List

Results 1 to 7 of 7
  1. #1
    Senior Member Joshua A.C. New's Avatar
    Join Date
    Aug 2007
    Location
    Northampton, MA
    My Bikes
    Iron Monkey: a junkyard steel 26" slick-tired city bike. Grey Fox: A Trek 7x00 frame, painted, with everything built, from spokes up. Jet Jaguar: A 92 Cannondale R900 frame, powder coated matte black with red and aluminum highlights.
    Posts
    957
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Drilling seat stay bridges for brakes

    (X-posted with the Mechanics forum)

    I just came across a nice, light steel frame yesterday and I'd like to use it for a project. The catch is, it's got canti bosses and they're both totally fuxx0rd.

    On the one hand, this is good, cuz I think I want to use dual pivot calipers anyway. On the other hand, it's not drilled for calipers.

    So what I'd like to do is drill for calipers and grind off the messed up canti bosses. The question is, how do I figure out if the seatstay bridge is in the right place? I could probably fab up a canti mount, if I had to, out of carbon fiber or something (I don't have the facility to weld or braze. That comes later.) but I need to know where it belongs first anyway.

    I also need to know if there's any reason that the bridge wouldn't be able to take the drilling.
    Joshua A.C. Newman,
    Passionate lover of construction

  2. #2
    Banned
    Join Date
    Aug 2005
    Posts
    5,117
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Wouldn't the manufacturer have the reach specified on their site, then you can check your frame. Canti wise all four can't be messed, a bird in the hand...

  3. #3
    Senior Member Joshua A.C. New's Avatar
    Join Date
    Aug 2007
    Location
    Northampton, MA
    My Bikes
    Iron Monkey: a junkyard steel 26" slick-tired city bike. Grey Fox: A Trek 7x00 frame, painted, with everything built, from spokes up. Jet Jaguar: A 92 Cannondale R900 frame, powder coated matte black with red and aluminum highlights.
    Posts
    957
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Only two mounts. Even if I could find the fork, I've got another I plan on using. One's wiggly and cracked, the other has had some sort of bull**** "repair" done to it.

    I don't know what the manufacturer is. It's short like a road racer, but has canti bosses. It's lighter than necessary for cyclocross, too.

    It came out of a dumpster into someone else's hands, they got flummoxed by the busted bosses, and now I'm falling into the same trap.
    Joshua A.C. Newman,
    Passionate lover of construction

  4. #4
    Senior Member Torchy McFlux's Avatar
    Join Date
    Sep 2007
    Location
    Vancouver
    My Bikes
    NOYB
    Posts
    1,397
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I used to know this number, but it's been a while since I was building frames.
    You need to borrow a measuring tape, a rear hub axle, and a road frame designed for caliper brakes. Stick the axle into the rear dropouts and measure from the center of that to the center of the caliper mount hole in the seatstay bridge. Do the same to your frame and if it matches, then get out the drill.
    Before drilling, be sure to measure, mark, and centerpunch the bridge carefully. you need that hole to be perfectly centered and square.
    Only trouble I can forsee is if the bridge is made of too thin steel. Then you may need to replace it with something else.
    Most cantilever bosses are brazed onto frames rather than welded. If this is the case in yours, there's an easier and safer way to get them off without grinding. Heat the bosses up with a torch until the braze flows, and they should pretty much fall off. Then you just have to file/sand off the remnants of braze on the tube.

  5. #5
    Framebuilder
    Join Date
    Dec 2007
    Posts
    472
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Put a wheel in the frame, measure from the center of the rim's braking surface to the center of the brake bridge where you would drill the mounting hole- if this measurement is 50mm or a little less just about any dual pivot caliper will work. If it's over 60mm it will fall into the mid-long reach brakes category.
    Other than the bridge being too thin, the other problem I see is that modern calipers are made to bolt to a flat surface and your bridge is probably round. The easy way around that is to find some old calipers that come with the concave spacers and as a bonus, they usually have longer reach than newer ones.
    All that said, I think the easier and better fix would be to replace the canti studs.

  6. #6
    Senior Member Nessism's Avatar
    Join Date
    Jun 2004
    Location
    Torrance, CA
    My Bikes
    Homebuilt steel
    Posts
    2,324
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Most common bridges are not strong enough for a brake. Typically the builder takes a piece of the seat stays and brazes it in place. A common brake bridge is at least twice as thick. Do what you want but I wouldn't mess around with something like this unless you know for a fact what the bridge is made out of.
    Last edited by Nessism; 09-18-08 at 09:59 PM.
    Becareful buying/selling bike parts on-line. I learned the hard way. :(

    Good/Bad Trader Listing

  7. #7
    Senior Member Joshua A.C. New's Avatar
    Join Date
    Aug 2007
    Location
    Northampton, MA
    My Bikes
    Iron Monkey: a junkyard steel 26" slick-tired city bike. Grey Fox: A Trek 7x00 frame, painted, with everything built, from spokes up. Jet Jaguar: A 92 Cannondale R900 frame, powder coated matte black with red and aluminum highlights.
    Posts
    957
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    All very good information, folks. I think I have to let this frame go.

    ... hmmm... unless it could become a fixie... then I could put on a fork that can take a brake...
    Joshua A.C. Newman,
    Passionate lover of construction

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •