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Old 09-08-09, 11:00 AM   #1
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slotting vs drilling fork for recessed nut?

I'm upgrading my caliper brakes and long story short the mounting bolt needs to go into the fork at an angle (with spherical washers) in order for things to fit right.

The problem, of course, is that if it goes in at an angle then it doesn't line up with the hole in the rear of the fork crown. So I'll have to drill a new hole (which is no biggie since I'd need a new hole to convert to a recessed nut anyway), but I'm leary of being able to figure out the correct position and the hole is going to partially overlap with the existing one.

Soooo, I was thinking it might be better to put an 8mm slot so I can adjust the angle of the mounting bolt after. Will the lack of support from the slot compared to a hole be a problem or the oblique mounting be a problem? I think not because Sheldon has recommended mounting brakes without even any support in the rear of the fork and typically the curvature of older style forks doesn't really support a flat recessed nut squarely anyway, but I wanted to get some opinions here before destroying my fork.

Last edited by chucky; 09-08-09 at 11:06 AM.
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Old 09-08-09, 11:45 AM   #2
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there should be enough room to use a short nut on the inside of the fork tubing that doesn't require any drilling.
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Old 09-08-09, 12:07 PM   #3
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there should be enough room to use a short nut on the inside of the fork tubing that doesn't require any drilling.
Yeah, but you still need a hole to tighten the nut....unless it's a regular wrench nut instead of a long recessed nut...good idea!
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Old 09-08-09, 12:20 PM   #4
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I'm trying to picture why the brake bolt would need to mount to the fork any other way than normal straight on. Trying to tweak the reach a little maybe? Maybe you need to re-think the brake choice. Kinda sounds like a recipe for trouble. A photo would sure help.
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Old 09-08-09, 12:25 PM   #5
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I'm w/norwood. Whatever you're doing, stop.
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Old 09-08-09, 01:04 PM   #6
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Well I didn't want to have to get into this, but here is a photo with the brake inserted straight on:
mal.jpg
and here it is inserted at an angle with spherical washers:
bueno.jpg

Reach is the same as the brakes I'm replacing, the problem is that the brake arms of the new brakes are raked/offset forward instead of dropping down parallel to the fork. Offset arms like this seem to be common among similar brakes and, while there are obviously brakes out which don't have rake (such as the ones I'm replacing), this is a 15 pound bike and the point here is to upgrade to something lighter with better stopping power without breaking the bank and as far as I know these are the only brakes which meet those requirements.

So I need to mount them at an angle. Is there any problem with that other than the fact that you guys just don't like it?
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Old 09-08-09, 01:07 PM   #7
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you need a longer reach caliper.

you also need a curved spacer meant for old style forks like that.

it's $25 for a tektro long arm.
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Old 09-08-09, 01:14 PM   #8
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you need a longer reach caliper.

you also need a curved spacer meant for old style forks like that.

it's $25 for a tektro long arm.
I do not need a longer reach caliper. The reach is exactly the same as the brakes they're replacing (which are not tektro long arm calipers or any other type of long reach brakes). I measured it and have lined them up side by side. It's the same down to the mm. The problem is the offset of the arms.

You see, this is why I didn't want to get into this, because you people are so full of yourselves that you can't offer whatever information you do have without admitting you don't know it all. I didn't want to get into this because I just wanted a little friendly help, but now I can see this is going to turn into a poop fight.

So please, just forget I posted the pictures and take my word that the brakes need to be mounted at an angle. Therefore, does anyone have any advice for mounting the brake at an angle?

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Old 09-08-09, 01:20 PM   #9
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the curvature of a wheel and how far the brakes stick out changes the reach required.

clearly you aren't ready for the internet and I suggest you jam a skewer through your modem.
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Old 09-08-09, 01:32 PM   #10
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the curvature of a wheel and how far the brakes stick out changes the reach required.
Therefore to solve the problem one can EITHER change the reach OR change how far the brakes stick out.

Since I have plenty of clearance I can change how far the brakes stick out by simply angling the mounting bolt and if there's no problem with this solution then I'd have to be a fool to follow your advice to soil my 15 pound bike with tektro long arm calipers; especially since the whole point of swapping the brakes is to get lighter brakes. Agreed?

Now, does anyone have an opinion on an angled brake mount? Possible issues? Best way to do it (file slot or hide nut in fork)?
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Old 09-08-09, 01:41 PM   #11
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I don't see a problem with mounting them at an angle in this case. I would drill a single hole rather than a slot, since I'd be a little worried about it loosening up- the force on the caliper when braking would tend to tilt the brake mounting bolt in such a way as to loosen it. If the mounting bolt came loose, the caliper could get stuck on the tire and you could crash.
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Old 09-08-09, 01:57 PM   #12
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If the mounting bolt came loose, the caliper could get stuck on the tire and you could crash.
Is this true? Because as I mentioned in the OP Sheldon Brown sometimes suggests not even mounting the bolt in the rear at all which would surely be worse than it coming loose if there were any danger.

Personally I don't believe there's any danger, but I am concerned that it might reduce braking performance if the one point mount allows the brakes to flex more because they are no longer as well supported by the fork crown. Do any of the real mechanics here think this a valid concern? The problem is I can't just try it because once I cut up the fork there's no going back.
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Old 09-08-09, 03:06 PM   #13
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It really isn't going to work. Assuming you did get it all mounted in the fork - which is at least going to require curved, beveled washers on either side of the fork on the mounting bolt - braking force is going to torque the caliper backwards. When mounted correctly the braking force pushes the caliper pretty much straight back, parallel to the mounting bolt (and with two contact points on the fork). Here the force will be pushing and a significant angle on the one contact and before long you'll have a bent bolt, if not a hole ripped in the fork, a caliper jammed in your wheel, and a face that will be thankful for Percoset.
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Old 09-08-09, 03:09 PM   #14
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Just for the sake of knowing - why the long "spacer" between the caliper and the fork? Did your old brake have the same arrangement? I've just never had one like that.

If you could cut that down you might acheive a two-point mount w/o drilling the fork.
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Old 09-08-09, 03:35 PM   #15
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If I had a 15 pound bike I wouldn't install the front brake unconventionally just for the sake of saving a few grams.
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Old 09-08-09, 03:51 PM   #16
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Is this true? Because as I mentioned in the OP Sheldon Brown sometimes suggests not even mounting the bolt in the rear at all which would surely be worse than it coming loose if there were any danger.

Personally I don't believe there's any danger, but I am concerned that it might reduce braking performance if the one point mount allows the brakes to flex more because they are no longer as well supported by the fork crown. Do any of the real mechanics here think this a valid concern? The problem is I can't just try it because once I cut up the fork there's no going back.
It's the slot I was concerned about- if the slot extends to the perpendicular, then the distance between the front hole and the top of the slot is greater than the distance between the front hole and the bottom of the slot. This means that the force from braking will tend to loosen the bolt. In Sheldon's case, the bolt is perpendicular to the fork crown, and therefore is neutral to tightening or loosening when braking. Personally I wouldn't trust anything on my braking system that relied only on friction to hold it in place against the direction of the major force vector. But it's your bike...

Edit- well, actually the threads on a bolt are held in place by friction, and I actually do trust brake bolts to hold in conventional mounting. But the mechanical advantage is way more.

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Old 09-08-09, 09:19 PM   #17
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When you already know more than any one else, why do you bother to post a question? Do as you have already decided to do, and live with the consequences. Maybe you'll learn something. Good luck.
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Old 09-08-09, 09:50 PM   #18
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In Sheldon's case, the bolt is perpendicular to the fork crown, and therefore is neutral to tightening or loosening when braking. Personally I wouldn't trust anything on my braking system that relied only on friction to hold it in place against the direction of the major force vector. But it's your bike...
The bolt being perpendicular or not depends on the angle of the surface of the crown and whether it is modified by spherical washers.

I just finished cannibalizing washers and such from the old brake to mount the new one at an angle, but without drilling the fork crown as suggested by AEO and I now have:

brake->anticup washer->cup washer->saddle washer->crown->antisaddle washer->cup washer->anticup washer->nut

This seems to give a good fit, but there's unfortunately not enough room on the bolt for a second nut to prevent the first from loosening, which is bad because this is the only nut holding things together (the front of the bolt is integrated to the brake arms). Also, unfortunately the impressive stack of washers weighs almost as much as the brake itself.

Quote:
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It really isn't going to work. Assuming you did get it all mounted in the fork - which is at least going to require curved, beveled washers on either side of the fork on the mounting bolt - braking force is going to torque the caliper backwards. When mounted correctly the braking force pushes the caliper pretty much straight back, parallel to the mounting bolt (and with two contact points on the fork). Here the force will be pushing and a significant angle on the one contact and before long you'll have a bent bolt, if not a hole ripped in the fork, a caliper jammed in your wheel, and a face that will be thankful for Percoset.
After reading your post I noticed that the mounting bolt from the old brake is bent in exactly the manner you describe. If what you say is true this would actually indicate that the braking force is pushing at an upward angle, in which case the angled mount would actually be the only safe option for exactly the reasons you give for it being more dangerous. In fact, looking at the pictures, it seems the root cause for both the torque and the reach/offset issue is actually the orientation of the braking surface and that the only thorough solution is to correct the angle of the mounting bolt to be tangent to that surface.

While I'm glad you pointed this out, it's a bit disconcerting as it now appears I'll be compromising safety if I don't figure out a way to make the unconventional angled mount work.

Quote:
Originally Posted by Bob Barker View Post
Just for the sake of knowing - why the long "spacer" between the caliper and the fork? Did your old brake have the same arrangement? I've just never had one like that.

If you could cut that down you might acheive a two-point mount w/o drilling the fork.
Not sure why, but the other brake has a similar spacer. It seems to ensure that the spring has enough clearance to operate without having interference from the fork.

In light of the washer difficulties and revelation above I might actually try filing this to agree with angled mount. However I'll have to be careful because on this particular brake that's where the CNC magic attaches the mounting bolt to the brake arms without any nuts.

Thanks for your input everyone. Does anyone have any more ideas?

Last edited by chucky; 09-08-09 at 10:31 PM.
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Old 09-08-09, 10:07 PM   #19
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When you already know more than any one else, why do you bother to post a question? Do as you have already decided to do, and live with the consequences. Maybe you'll learn something. Good luck.
Because just because I know more about some particular thing it doesn't necessarily mean I know more about everything. My interaction with stausty above is a perfect example: Although he had a great insight, without some key facts his conclusion was the opposite of the truth. Fortunately he was gracious enough to share what he knows (an idea about how the braking surface might torque the mounting bolt) without stubbornly insisting on what he doesn't know (the answer) and as a result I was able to combine that with what I know (facts about the brakes in hand) in order to get a better idea of what the answer might be.

The best way to learn something is for everyone to share what they know and the problem with most experts is that they're too proud to accept that although they might know many things that doesn't necessarily mean they know the answer and they refuse to share their knowledge but instead insist on stroking their own egos by pretending to know the final answer so they don't have to share the credit with anyone else (god forbid it be a person humble enough to ask a question). That's why I think it's best to treat experts like inanimate objects: although they're too stupid to learn, you can still glean a lot of useful information by observing and probing them and even if you know more than them you can still learn a lot.

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Old 09-08-09, 11:22 PM   #20
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I think you're way out of line and in way over your head. Why don't you contact the maker of the brakes and get their opinion of how their product should be mounted. Considering the very limited information that you have grudgingly passed along, opinions were made. Advice you've been given has been in your best interest (right or wrong in your eyes). I say do whatever you please and keep it to yourself.
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Old 09-09-09, 12:59 AM   #21
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in reality, none are experts. all are apprentices. mount your brake however you want. you
will learn something about brake mounting and hopefully something about yourself in the process.
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Old 09-09-09, 04:05 AM   #22
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Old 09-30-09, 12:35 PM   #23
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This is turning out to be a real ***** to get working. The problem is that the fork crown is curved and since the recessed bolt doesn't reach the back wall of the fork crown I need tighten against the back of the front wall of the fork crown. This is a problem because the back of the front wall of the fork crown is female conical in shape (ie vertically flat and horizontally concave), which means I need a male conical washer (ie vertically flat and horizontally convex) to correct it and, as far as I can tell, male conical washers don't exist.

Ironically the problem has nothing to do with the angled mounting, but simply the incompatibility between short/recessed brake bolts and curved fork crowns. Is there any way to fix this? I'd just bend the fork crown flat, but it's aluminum. I guess I could get some thick serrated washers and file them to shape unless anyone has a better idea?
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Old 09-30-09, 12:55 PM   #24
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This is turning out to be a real ***** to get working.
You've been fighting with this for 3 weeks. That's too long to be fighting with a brake caliper.

Could we go back to the very beginning? Why does the brake caliper mounting bolt have to go in at an angle? In your original post you kind of skipped over that item and that seems to be at the crux of your problem.

PM me if you want. I promise that I'll stick with you until you get this figured out or for as long as you want - whichever comes first.
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Old 09-30-09, 02:38 PM   #25
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You've been fighting with this for 3 weeks. That's too long to be fighting with a brake caliper.

Could we go back to the very beginning? Why does the brake caliper mounting bolt have to go in at an angle? In your original post you kind of skipped over that item and that seems to be at the crux of your problem.

PM me if you want. I promise that I'll stick with you until you get this figured out or for as long as you want - whichever comes first.
Ok. The real reason the bolt needs to go in at an angle is twofold:
1. This is a folding bike with an 8-inch diameter wheel, subsequently the rim curves downward rather abruptly and is only horizontal very close to the fork crown.
2. All modern light weight caliper brake arms seem to sweep forwards into this region where the rim is not horizontal. Presumably the purpose of this feature is to clear large diameter carbon fork blades (which I don't have).

Therefore it will not be possible to use a horizontally mounted light weight brake because the distance from the fork crown to the brake arms on such brakes is so large that the brake pads would need to be mounted semivertically in order to be parallel to the rim, which would make them grab as much tire as they do rim (if they even reach the rim at all). Moreover, inspection of the stock brake reveals that, contrary to the stock design of this bike, it probably isn't a good idea to use a horizontal mount at all because the tangent direction of the rim is itself angled downwards except for directly between the fork blades (basically underneath the crown) and consequently causes horizontally mounted bolts to bend by pulling them downwards.

However, this is not the crux of the problem because double spherical cup washers are designed to accomplish precisely such angled mounts because the male (convex) spherical washer can be pointed in any direction while still maintaining full contact with the female (concave) spherical washer (like a socket). The crux of the problem is the fact that fork crown surface is itself not even flat and therefore can't mate to the flat washers such as the back side of a cup washer or simply a normal flat washer. This is traditionally solved with a female cylindrical washer ("cylindircal" because they only curve in one direction, not both directions like the spherical washers) on each the front and back outside surfaces of the fork crown, but that won't work here because the (only) nut securing the brake is being mounted to the inside of the fork crown (which is female/concave) instead of the outside.

So I think I've figured it out, I just have to make a male (convex) cylindrical washer to flatten the inside of the fork crown. Then the fork crown surfaces will be flat and I can simply use the spherical washers to adjust the angle.
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