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  1. #1
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    I drilled both sides...now what?

    I wanted both front and rear brakes on my single speed conversion. I bought recessed brakes and didnt realize I couldnt mount them as is. I read something about drilling out the rear bridge to mount it. I acted hastily and drilled both the front and back of the rear bridge. The recessed nut fits just barely in the hole, great. However, now I read that you only want to drill out the front and not the back. Well, crap. I know, I acted to quickly.
    Now that I have both sides of the rear bridge drilled out, can someone explain to me what the drawbacks are of that? Does the brake move around? Do I run the risk of actually bending out the rear bridge with hard braking? I just want to get an idea of where I stand here.

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    I would imagine you would have enough material in the bridge to be safe. See if your LBS has either a shim or a spare nut that you can drill out to the size of the bolt on the brake and stick it through the back side. It would probably have to be shortened quite a bit but all you want it to do is take up the space between the brake bolt and the hole.

    Hope this makes sense.

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    slow as I ever was Ex Pres's Avatar
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    If you're brake bridge is solid, you have no worries. If it's a hollow bridge, stick a plastic insert in the back side/outside to help keep it solid.

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  4. #4
    BeaverTerror Yan's Avatar
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    This reminds me of that guy who tried to remove his dork disk by setting it on fire.
    Yan

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    Senior Member cyclist2000's Avatar
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    I think that you could use one of these flat washers on the front side. you may also need a long recess bolt due to the additional thickness of the washer.
    http://loosescrews.com/index.cgi?d=s...id=99621688357
    I had a similar situation where I was using an old set of brakes (non-recessed) on a frame that had a recessed brake bridge. I took a recess nut and drilled it out to 6mm and used it as a shim, that may be a possibility for the front side, but I think that you would want the area that the caliper rests on the brake bridge to be larger than the shim to better hold it in place, so the above washer is probably a better idea.
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    Quote Originally Posted by Ex Pres View Post
    If you're brake bridge is solid, you have no worries. If it's a hollow bridge, stick a plastic insert in the back side/outside to help keep it solid.

    http://www.rivbike.com/products/show...-insert/15-052
    This (more or less) was what I was suggesting using a drilled out nut (insert type)

  7. #7
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by Ex Pres View Post
    If you're brake bridge is solid, you have no worries. If it's a hollow bridge, stick a plastic insert in the back side/outside to help keep it solid.

    http://www.rivbike.com/products/show...-insert/15-052
    You used to be able to get these in brass. Perhaps the LBS still has some?

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    Don't sweat, you couldn't have only drilled out the front anyway since you have to drill back to front. (the seat tube is in the way otherwise). No serious crisis here if the bridge has a flat face or square boss in the center, but you want to stabilize the brake on the bridge.

    Find a nut long enough to reach the full depth, and trim it to be just short of bottoming out so it supports the business end of the brake. You might have to drill out some thread if the bolt isn't fully threaded. Or buy another brake nut, cut off ( if necessary drill out) a section to make bushing and glue it to the base of the brake bolt to bring it out tom the diameter of the hole.

    If you want to get fancy, you can make a stepped washer that fits nicely onto the bridge shoring it up, protecting the face and restoring a 6mm hole in back.

    Anyway that ensures that the brake bolt cannot shift at it's base is fine, and as I said, drilling it through was your only option.

    If your bridge was a simple hollow tube, it's more complicated because there isn't much structure there, and the large hole might need lots of reinforcing. Come back if that's the case.
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    Raving Madman deathshadow60's Avatar
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    Quote Originally Posted by JohnDThompson View Post
    You used to be able to get these in brass. Perhaps the LBS still has some?
    Aubuchon Hardware, Home Depot... It's a flat washer, brass, steel, plastic - dive for the bins.

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    Quote Originally Posted by Yan View Post
    This reminds me of that guy who tried to remove his dork disk by setting it on fire.
    Not even in the same league. That guy was classic.

  11. #11
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    Thanks for the replies, but I want to make sure we are speaking about the same thing, so I took some pictures. The bridge is marred up, yes, I know, but I am going to strip it and powdercoat it so no worries there. The thing about this is, the nut is nice and long and fits almost all the way through the rear bridge, that is why I drilled out both sides. You can see in these pictures a view of the back of the bridge and the front of the bridge. Also a picture of just the drilled hole. I have a lock nut with the brake assembly that I will put on the back side of the bridge between the nut and the brake assembly, so it should hold it nice and snug.
    When you look at the pictures, does it look like there is enough material to hold? Or does it look like, with hard braking, the material that is there will end up breaking off or stripping out? Basically, does it look like this setup is safe?
    Attached Images Attached Images

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  13. #13
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    Quote Originally Posted by roberth33tiger View Post
    And one of those would be mounted on the back between the lock washer and the recessed nut, right? Is this for stability? I am really trying to understand what I am shooting for here. Also, does it look like there is enough material there to hold the brake?

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    My recommendation is to get a short recessed nut and drill it out to 6mm, and saw it off very short and perhaps file the flange thinner. I.e. make your own support bushing to support the back side of the brake bolt.

    BTW, FBinNY isn't quite right. You can drill out just the front of the rear bridge. You take a 5/16" or 8 mm short drill bit and clamp it sideways in a Vise-Grip. Then you turn it a fraction of a turn at a time to enlarge the front hole only. It's slow and a bit laborious but it does work. You are only removing a small amount of metal and the existing 6 mm hole acts as an accurate centering quide.

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    Quote Originally Posted by HillRider View Post
    My recommendation is to get a short recessed nut and drill it out to 6mm, and saw it off very short and perhaps file the flange thinner. I.e. make your own support bushing to support the back side of the brake bolt..
    Pardon my ignorance, but what do you mean drill it out to 6mm?
    Would the use of one of these washers on the back solve the problem? http://www.niagaracycle.com/product_...ucts_id=425726
    Would that be enough support?

    Also, does it look like there is enough metal there to hold the brake securely?

  16. #16
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    Quote Originally Posted by HillRider View Post
    BTW, FBinNY isn't quite right. You can drill out just the front of the rear bridge. You take a 5/16" or 8 mm short drill bit and clamp it sideways in a Vise-Grip. Then you turn it a fraction of a turn at a time to enlarge the front hole only. It's slow and a bit laborious but it does work. You are only removing a small amount of metal and the existing 6 mm hole acts as an accurate centering quide.
    Yes that would work for a hollow tubular type of bridge, which could much more easily be opened up with a tapered reamer, but unfortunately shouldn't be drilled because it lacks structure. If it had a solid or reinforced boss in the center it would take eons hand turning a drill bit.

    Now the OP has two choices,

    First and best in the long term, have someone, or himself if he's up to the task, fabricate a proper stepped insert with a brake mounting face and silver solder it in place.

    Second, find a piece of scrap aluminum bar, about 9/16" in diameter, and long enough to work with. Face off both ends to a length about 1/8" greater than the diameter of the bridge. Drill straight across with a drill equal to the bridge diameter. Drill axially with the appropriate drills to form the stepped inside, 6mm at one end, and 8mm matching his recess nut at the other. Finish by carefully sawing down the middle, so it can clamshell around the bridge supporting it externally from crushing. He can do the job with a drill, hacksaw and file though a drill press and/or a lathe would make it far simpler.

    he'll probably also need to make a small 8mm OD spacer to support the brake side of the bolt in the bridge.

    When it's done and assembled 100% to his satisfaction he can improve the rigidity by super gluing the parts to the bridge, using the mounted brake to hold it while it sets. The glue bond needn't be great, it's only to provide traction in shear while the brake holds it together.

    BTW- cheap bikes of the era used 1/2 round spacers similar to what he's making for rear brake mounting, except both halves were drilled 6mm for a bolt and nut. If he can find a pair of these with the right curvature for his bridge, all he needs do is drill one side for the recess nut.

    I have a small piece of aluminum appropriate to the job left over from producing axle and chainring spacers, and if the OP wants, I'll sent it to him fro free. I also have a pair of old spacers which might save him a bit of labor.
    Last edited by FBinNY; 03-09-10 at 12:23 PM.
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    Does look rather thin but, hard to tell even with your good photos. The concave washers mentioned by roberth33tiger might be worth some consideration.

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    Quote Originally Posted by marcusedvalson View Post
    Pardon my ignorance, but what do you mean drill it out to 6mm?
    Would the use of one of these washers on the back solve the problem? http://www.niagaracycle.com/product_...ucts_id=425726
    Would that be enough support?
    Those washers are just external and do nothing to position the brake's bolt within the hole.

  19. #19
    bike whisperer Kimmo's Avatar
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    Quote Originally Posted by roberth33tiger View Post
    I reckon you could use two.



    If you drill em out, the recessed nut should be through both of em, but it shouldn't protrude, otherwise you'll have to cut, file or grind it shorter.

    That'll be fine. Even if it doesn't go through the upper one, it should be alright.

    Quote Originally Posted by HillRider View Post
    Those washers are just external and do nothing to position the brake's bolt within the hole.
    The hole is sized for the recessed nut, isn't it? They'll spread the load enough for the brake bridge not to be damaged, as long as the curve's a good match. I've used that setup before for years with no worries... it's prolly only 50% stronger than it needs to be, though.


    ...Also, if you paint those bits to match the frame, no-one will pick the hack job : )
    Last edited by Kimmo; 03-09-10 at 06:38 PM.

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    Quote Originally Posted by Kimmo View Post
    I reckon you could use two.



    If you drill em out, the recessed nut should be through both of em, but it shouldn't protrude, otherwise you'll have to cut, file or grind it shorter.

    That'll be fine. Even if it doesn't go through the upper one, it should be alright.

    The hole is sized for the recessed nut, isn't it? They'll spread the load enough for the brake bridge not to be damaged, as long as the curve's a good match. I've used that setup before for years with no worries... it's prolly only 50% stronger than it needs to be, though.


    ...Also, if you paint those bits to match the frame, no-one will pick the hack job : )
    I went to the bike shop today and the mechanic gave me two of those washers for free. How nice! The only thing is, I dont think I will need one on the front side of the bridge. The recessed nut fits perfectly snug in that hole and there is a lip that keeps it from pulling through. Are you thinking the purpose would be just to spread the load on the front side also?

  21. #21
    bike whisperer Kimmo's Avatar
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    Yeah, it'd be a good move... don't you think the brake bridge looks a little flimsy with that big hole in it?

    Most of em have a flat section for the brake to sit on.

    Oh yeah - obviously, you won't need to drill the upper one out if the nut doesn't poke through the tube.

  22. #22
    Senior Member Torchy McFlux's Avatar
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    Quote Originally Posted by HillRider View Post
    Those washers are just external and do nothing to position the brake's bolt within the hole.
    Yup.
    If the frame is getting stripped and repainted, why not get a framebuilder to just braze a new bridge in there? It will be the proper recessed bolt type, won't require jury-rigging, and will probably cost you about the same as getting some bottle bosses installed.

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    Quote Originally Posted by HillRider View Post
    BTW, FBinNY isn't quite right. You can drill out just the front of the rear bridge. You take a 5/16" or 8 mm short drill bit and clamp it sideways in a Vise-Grip. Then you turn it a fraction of a turn at a time to enlarge the front hole only. It's slow and a bit laborious but it does work. You are only removing a small amount of metal and the existing 6 mm hole acts as an accurate centering quide.
    Quote Originally Posted by FBinNY View Post
    Yes that would work for a hollow tubular type of bridge, which could much more easily be opened up with a tapered reamer, but unfortunately shouldn't be drilled because it lacks structure. If it had a solid or reinforced boss in the center it would take eons hand turning a drill bit.
    Is it safe to widen only the front hole of a hollow tubular bridge with a tapered reamer?

    I'm doing this same kind of project as the OP so that I can mount a set of Tektro R556 brakes on my Panasonic. I only mounted the front brake on the fork (a piece of cake) because I was afraid of compromising the integrity of the hollow tubular bridge for the rear brake.

    I couldn't find a tapered reamer at my nearby Home Depot. This was the best that I could find.

  24. #24
    bike whisperer Kimmo's Avatar
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    If it looks like this, I reckon it's strong enough.



    Looks fairly neat too, especially if you file the lower washer into a cone.

  25. #25
    Senior Member BCRider's Avatar
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    Lovely sketch to show what is needed Kimmo.

    Marcus, you need the concave washer on the front side as well since the wall of the tube would collapse when you try to tighten the tube nut down if there's no concave washer to help spread the load. What Kimmo shows is what you need to duplicate. This means you'll need to drill out one washer to accept the tubular nut and leave the other a snug fit on the caliper stud to support the caliper from trying to pivot down and under. And because the washer will be taking quite a bit of the load due to you drilling both sides you want that washer to be a nice fit to the curve of the tube.
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