Bicycle Mechanics - 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.

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.

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/images/products/full/0000/1236/brakeinsertIIN.jpg
http://www.rivbike.com/products/show/brake-insert/15-052

This reminds me of that guy who tried to remove his dork disk by setting it on fire.

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=single&c=Brake&sc=Washers&tc=&item_id=DC-B51&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.

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/images/products/full/0000/1236/brakeinsertIIN.jpg
http://www.rivbike.com/products/show/brake-insert/15-052

This (more or less) was what I was suggesting using a drilled out nut (insert type)

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/images/products/full/0000/1236/brakeinsertIIN.jpg
http://www.rivbike.com/products/show/brake-insert/15-052
You used to be able to get these in brass. Perhaps the LBS still has some?
http://www.os2.dhs.org/~john/washer.jpg

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.

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.

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.

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?

looks like you might need these:
http://www.niagaracycle.com/product_info.php?products_id=425726

looks like you might need these:
http://www.niagaracycle.com/product_info.php?products_id=425726
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?

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.

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_info.php?products_id=425726
Would that be enough support?

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

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.

Does look rather thin but, hard to tell even with your good photos. The concave washers mentioned by roberth33tiger might be worth some consideration.

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_info.php?products_id=425726
Would that be enough support?
Those washers are just external and do nothing to position the brake's bolt within the hole.

looks like you might need these:
http://www.niagaracycle.com/product_info.php?products_id=425726

I reckon you could use two.

http://www.niagaracycle.com/images/qbpimages/BR2039md.jpg

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.


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 : )

I reckon you could use two.

http://www.niagaracycle.com/images/qbpimages/BR2039md.jpg

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?

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.

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.

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.
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. (http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?jspStoreDir=hdus&catalogId=10053&productId=100352516)

If it looks like this, I reckon it's strong enough.

http://i40.tinypic.com/ofd7on.jpg

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

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.

If it looks like this, I reckon it's strong enough.

http://i40.tinypic.com/ofd7on.jpg

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

WOW! Nice illustration, how'd you do it?

Adding and subtracting simple selections, filling them, contracting the selections a couple of pixels and cutting. Layers helped. Proportions and centering just done by eye.

If it looks like this, I reckon it's strong enough.

http://i40.tinypic.com/ofd7on.jpg

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

The sketch shows what a decent approch would look like in cross section, which as i posted earlier is exactly how brakes were mounted years ago, except for the use of a hex nut vs. a through bolt and nut.

A minor quibble; in the sketch only the rear is drilled out to 8mm, but the OP drilled out both sides. That would allow the bolt to rock in the front hole. To solve that an 8mm bushing would need to be added to the back of the bolt to fill the front hole and stabilize it. One approach would be to drill both washers out to 8mm (matching the frame) and fit a drilled out and cut down mounting nut from the front also. (possibly Kimmo would be kind enough to modify the sketch showing how)

Also note that the curvature of the nuts needs to be a close match to that of the bridge, A bit of mismatch is OK, as the bridge will ovalize when the sandwich is compressed, but you want to avoid over distorting the bridge.

To those with similar frames, I suggest seeing if the bolt of a front brake is long enough, and if so drilling the bridge only 6mm and installing the brake with 2 concave washers and a regular nut on the back.

A little update. I did exactly what was illustrated by Kimmo last night. The only problem that arose was the drilled out washer on the front side of the bridge prohibited me from getting the brake nice and tight on that bridge. I took another gamble and removed that washer on the front part of the bridge and tightened it. Turns out that it worked like a charm. I was able to get the whole brake assembly nice and tight on that bridge and now it doesnt move at all. The only question I have is, over time do you think the recessed nut will wear out the front side of the bridge? Also, are there any pointers for getting the nut tight with the concave washer on the front side?

A little update. I did exactly what was illustrated by Kimmo last night. The only problem that arose was the drilled out washer on the front side of the bridge prohibited me from getting the brake nice and tight on that bridge. I took another gamble and removed that washer on the front part of the bridge and tightened it. Turns out that it worked like a charm. I was able to get the whole brake assembly nice and tight on that bridge and now it doesnt move at all. The only question I have is, over time do you think the recessed nut will wear out the front side of the bridge? Also, are there any pointers for getting the nut tight with the concave washer on the front side?

see my post immediately above. If you drill out the brake side concave washer so as to make a sandwich a la Kimmo, but with a drilled out recess nut behind the brake and extending into the bridge enough stabilize the front washer you'll get more support and rigidity.

Remember to use loctite on the nut.

When converting to recessed brakes, I built a similar aluminum block to reinforce the bridge. It is glued in place with epoxy. The block is larger, so that when clamped down it does not compress the bridge and the joint has the correct epoxy bondline. The brake was installed with a homemade recessed nut.

http://img39.imageshack.us/img39/2600/img1675w.jpg

you all do realize the next posing from this member will be "the brake pads on my short reach calipers do not reach the 700c wheels on my 27" frame"

A minor quibble; in the sketch only the rear is drilled out to 8mm, but the OP drilled out both sides. That would allow the bolt to rock in the front hole.
I was replying to this post:

Is it safe to widen only the front hole of a hollow tubular bridge with a tapered reamer?
And I'm pretty sure the oversize top hole isn't an issue in practice; the curved washer holds the spindle in place just fine, as long as it's hole isn't oversized. Even then, I doubt it's a big deal unless you're in the habit of rocking the bike back and forth while holding the rear brake.

Does your frame have cable mounts for a rear brake? Most fixed gears/track bikes only run with a front brake because thats all you really need (you slow the back wheel yourself by pedaling backwards). However, most single speed frames will support a rear brake. You should not bend your rear bridge unless the hole which you drilled takes up almost the entire diameter of the bridge. If I were you I would only run a front brake just to be sure. The extra brake on the rear doesn't help that much considering 90% of your stopping power comes from your front wheel, and you get your legs contributing to the rear to flatten your bike out (Just a better workout). I see a lot of hipsters running around with no brakes, and relying on a skid to slow. I don't agree with this because its hard to control without your front brake.

It's demented.

Man this thread got overthinked. Did this exact same mod to a friends bike years ago, installed some tektro dual pivots onto it. Been, working and has held up just fine.