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How dangerous is this?

Old 03-28-18, 10:53 PM
  #1  
tarsi 
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How dangerous is this?

Looking for options other than drilling back hole of fork. Was able to attach recessed nut and tighten to the stub that made it through the first hole. Am I better off using a standard nut, extending the stub with a coupler and exiting out the rear hole or am I simply playing with fire and need to find a nutted brake set?
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Old 03-28-18, 10:57 PM
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don't do what you just did (except to check fit of the brakes). go get a coupler for like $2 and use that. I did the same on my semi-pro. front brake on rear, rear brake with coupler extension.
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Old 03-29-18, 12:14 AM
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Check this thread for an alternative solution:

Retro Roadie braking joy

You can get a long pivot bolt for under $10 on eBay, and if you don't forget to take out the set screws it doesn't take much longer than changing out brake pads. The coupler solution will work, and there's less risk of screwing up your brake that way, but replacing the pivot bolt is just such a clean solution.
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Old 03-29-18, 02:53 AM
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What kind of of fork is that that doesn't have a rear hole drilled? The forces on a front brake are huge and a double-hole fixation is so much more stable. A construction that puts "bending load" on a threaded bolt is inherently a bad idea.
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Old 03-29-18, 05:35 AM
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Probably will fail with first use. Dangerous? Well that is dependent on why you are using the brake!
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Old 03-29-18, 05:46 AM
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Playing with fire.
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Old 03-29-18, 06:05 AM
  #7  
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These - cheap, safe, effective.

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Old 03-29-18, 07:18 AM
  #8  
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Originally Posted by martl View Post
What kind of of fork is that that doesn't have a rear hole drilled?
It probably is drilled all the way through, it just appears that the OP is trying to mount a caliper intended as a rear caliper into the fork. Front calipers have longer pivots that reach all the way through the crown.
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Old 03-29-18, 07:57 AM
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The fork does have a hole in the back it's just not large enough for the recessed nut to fit. Some have suggested drilling the hole larger and using a longer recessed nut. I prefer not altering the fork.

The brake set I'm using is recessed. I'm actually using the rear brake up front as it was too short for the back. Neither the rear nor the front brakes are long enough for the front.

I'm leaning towards the coupler solution vs disassembling the brake and replacing mounting screw with a longer one assuming it will be sufficiently strong to support the forces. Mechanical engineers?

Last edited by tarsi; 03-29-18 at 08:00 AM. Reason: Typo
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Old 03-29-18, 08:29 AM
  #10  
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Originally Posted by tarsi View Post
The fork does have a hole in the back it's just not large enough for the recessed nut to fit. Some have suggested drilling the hole larger and using a longer recessed nut. I prefer not altering the fork.

The brake set I'm using is recessed. I'm actually using the rear brake up front as it was too short for the back. Neither the rear nor the front brakes are long enough for the front.

I'm leaning towards the coupler solution vs disassembling the brake and replacing mounting screw with a longer one assuming it will be sufficiently strong to support the forces. Mechanical engineers?
I read somewhere that recessed nuts should always cover at least 6 threads of the brake bolt to safely handle the various loads. My non-professional logic therefore thinks a coupler inside the steerer would need to cover 12 threads or more (6 in each direction) to arrive at equivalent peace-of-mind.
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Old 03-29-18, 08:37 AM
  #11  
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So you're gonna get an m6 coupler nut and an m6 bolt to screw into the coupler from the back? Assuming they're all steel and graded you should be fine strength-wise, in fact there will be a lot more metal with the coupler nut and an m6 bolt in there. For more strength you can get a grade 8.8 bolt rather than an ungraded one.

Sheldon Brown suggests exactly what you've done but John Allen added a note about how this doesn't counteract the tendency of the brake to rotate forward. Personally I think if the fork crown is thick and you really torque the brake nut down it would be strong enough to resist this force but I am not a mechanical engineer which is why I would just drill the back hole of the fork out.
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Old 03-29-18, 10:47 AM
  #12  
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How dangerous is this?
Make sure that your affairs are in order! That is extremely dangerous! My opinion, of course.
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Old 03-29-18, 10:56 AM
  #13  
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Originally Posted by clasher View Post
So you're gonna get an m6 coupler nut and an m6 bolt to screw into the coupler from the back? Assuming they're all steel and graded you should be fine strength-wise, in fact there will be a lot more metal with the coupler nut and an m6 bolt in there. For more strength you can get a grade 8.8 bolt rather than an ungraded one.
this is exactly what I did with mine. probably just widening the hole slightly is actually the better solution (as this does not stop one from going back to a nutted brake) but I liked the experiment Note: I had to use a grinder on my coupler nut so that it could fit in there- but just shaved a bit off each side and it went in nice and snug. easy enough. just spin the brake on while adjusting the coupler so its all snug- m6 bolt in the back and you are good to go.
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Old 03-29-18, 11:02 AM
  #14  
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found a pic:

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Old 03-29-18, 01:28 PM
  #15  
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Originally Posted by thinktubes View Post
These - cheap, safe, effective.

What are those called? Where do you get them?
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Old 03-29-18, 01:32 PM
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Depending on the brake, you can buy new pivot bolts.

Somewhere halfway down the page, there are some at Toronto Titanium.

Paul Brakes, Titanium Dura Ace, CNC Bike Brakes, Brake Post Studs



If you have the brake model number, you can also look up on Shimano's part diagrams, then search for the part number to find OEM parts.
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Old 03-29-18, 01:36 PM
  #17  
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Originally Posted by USAZorro View Post

What are those called? Where do you get them?
Recessed Brake Nuts.

That photo was apparently from E-Bay. I would assume most bike shops would also sell them.

TorontoCycles also has them in Titanium. Same link as above. Lengths from 13mm to 60mm.



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Old 03-29-18, 05:45 PM
  #18  
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He is right.

Originally Posted by jetboy View Post
don't do what you just did (except to check fit of the brakes). Go get a coupler for like $2 and use that. I did the same on my semi-pro. Front brake on rear, rear brake with coupler extension.
+1
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Old 03-29-18, 07:51 PM
  #19  
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I just wanted to address any concerns that the bolt needs to be supported at two points, some distance apart.

Actually, it does not. There should be no rocking at all, nor any bending loads fed into the bolt at all, IF the bolt is tensioned near spec, and if the (usually toothed) support surface is of the specified diameter.

For any bending load or rocking to affect the bolt would require that the bolt was not tensioned fully, or that the washer surface was somehow of reduced area, since the bolt's pre-load tension is fully sufficient to prevent the mounting surface of the caliper (at the toothed washer) from ever moving. Again though, the mounting surface of the caliper centerbolt's "hub" must be of at least the original diameter to assure that the bolt's specified tension prevents it from ever rocking in response to the heaviest braking loads.
The Cheltenham-Pedersen that I have raced for over 20 years mounts it's front caliper to a sheet-metal plate of sorts, with the nut capturing just the thickness of that plate. The rather thin plate itself flexes, but the caliper mounting sure doesn't!

Looking at the installation, my only concerns are that at least four threads are engaged, and that the nut meeting the inside of the steer tube is not perhaps preventing the nut from being torqued properly, though at the nut's small diameter there I don't think that there would be any excess of friction resisting the nut being fully torqued.
One might also speculate of the possibility that the steer tube and crown could somehow be weakened by the localized stress of the nut pressing against the inside, but that seems unlikely and a washer could be used if either of these remote potential "issues" was a concern.

So I am giving this installation a thumbs-up.

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Old 03-29-18, 08:15 PM
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be fun to test. and lo! i happen to have a pocket lab! if i get a chance ill test the acceleration of a brake with the bolt with 2 points vs 1 point. might be able to get to it tomorrow if I remember to bring it in to work. (sticks in bag now). easy enough to see if one has larger amplitude vibrations than the other.
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Old 03-29-18, 10:20 PM
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Originally Posted by jetboy View Post
don't do what you just did (except to check fit of the brakes). go get a coupler for like $2 and use that. I did the same on my semi-pro. front brake on rear, rear brake with coupler extension.
M6 coupling nuts can vary in length, the examples I have used required a bit of grinding to reduce the length a wee bit. I grind both ends to assist in the nut fitting against the inside of the steerer. The finish off with a chrome plated button head cap screw, to add strength and provide a nice finish.
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Old 03-29-18, 10:39 PM
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Picked up a coupling today and it fit inside the fork without grinding.

To maximize amount the caliper rod goes into the coupling, I removed the toothed washer that usually goes between the caliper and the fork. Is there any problem with doing this? Is it preferable to use the washer and not have the mounting rod go as deep into the coupling?

I've included a picture of the rear brake with the toothed washer to help clarify what I am talking about.
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Old 03-30-18, 06:15 AM
  #23  
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Originally Posted by tarsi View Post
Picked up a coupling today and it fit inside the fork without grinding.

To maximize amount the caliper rod goes into the coupling, I removed the toothed washer that usually goes between the caliper and the fork. Is there any problem with doing this? Is it preferable to use the washer and not have the mounting rod go as deep into the coupling?

I've included a picture of the rear brake with the toothed washer to help clarify what I am talking about.
suspect the toothed washer's primary role is to secure the brake from swiveling away from desired centerline, and that if the slightly freer mounting works for you, the brake's main bolt shoulder will distribute load just fine without the washer.
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Old 03-30-18, 06:21 AM
  #24  
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Originally Posted by USAZorro View Post
What are those called? Where do you get them?
Sex bolts *titter*

Fastener suppliers have them, or bike shops are littered with them.
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Old 03-30-18, 06:24 AM
  #25  
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Originally Posted by wschruba View Post
Sex bolts *titter*

Fastener suppliers have them, or bike shops are littered with them.

See them regularly on door closers and other hardware applications such as bathroom accessories and partitions. Lowe's and Home Depot will have them in their hardware fastener section.

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