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Spinning Cantilever Stud

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Spinning Cantilever Stud

Old 01-03-12, 04:23 PM
  #1  
roburrito
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Spinning Cantilever Stud

I went to change the brakes on my touring bike and while screwing in the brake the stud started to spin! Not sure what to do. Can I tighten it back down or does it need to be re-brazed? Or do I need to replace the entire boss?






Second picture is off the opposite stud. I can't remove the brake from the spinning stud.
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Old 01-03-12, 04:56 PM
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Doing it right, a proper repair, with the oxy- acetylene torch you,
or your frame repair tech/ welding shop person,
can burn off most of the paint, then drill out the swaging, that star like punched in part
so the boss can be removed from the base, then clean up those surfaces ,
to get the brass to bond well.. flux and re-braze it back in place..

one of the 2 didnt stay brazed in place, builder should have brazed the boss,
the round part to the base, the folded sheet part
then the whole thing to the frame..

I had a similar repair on my bike, took about 25 years before it came loose.
I did braze the pivot to the base, when I fit the braze ons.
there is a little bit of loosening action every time the brake is applied.

If bolt comes off but the caliper does not , bolt likely was overtightened
and mushroomed the end of the brake boss.
bang on it , maybe with a wooden punch to not dent the aluminum ,
and get out the hammer,,

if it spins it needs to be brazed on , perhaps builder skipped that part,
or did not get good penetration..

the factory was really miserly on the brass .. weak QC.

Last edited by fietsbob; 05-24-16 at 09:48 PM.
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Old 01-04-12, 11:58 AM
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Odds are you can do a decent job without resorting to a torch. The back swage looks like enough to hold it on, but obviously isn't enough to keep it from spinning. First remove the brake and feel if the stud is loose enough to wiggle, or only enough to spin. If it wiggles a bit it might still be OK, but will cost you some rigidity in the brakes, possibly needing to be compensated with extra toe-in.

If it's firm run some naphtha or minerl spirits into the joint to wash out any oil, then acetone into the to clean it down to dry bare metal. Repeat the acetone wash a few times to be sure it's truly clean, then allow to dry for a few hours. Now wick some super glue into the joint, both from the front and back, and allow that to cure overnight. If you prefer, Locktite and others make a wicking grade designed for situations like this, but again cleanliness is critical to a good job.

Now you should be able to mount the brakes and tighten the bolt properly.
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Old 01-04-12, 12:16 PM
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pop that damn thing out, go to your local shop and pick up some v-brake bosses and then go to a hardware store and find a lock washer and nut to fit the back of it, then you will have a replaceable boss if the inside ever gets stripped
Some advice for another forum. I like the idea, thoughts?
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Old 01-04-12, 12:26 PM
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Originally Posted by roburrito View Post
Some advice for another forum. I like the idea, thoughts?
"there was a young lady who swallowed a fly....."

Rule one in mechanics, start with the simplest, least invasive solution.

The threaded stud would probably work, but the solution is harder than gluing what you have.

Note also, that it isn't a reversible process. Make sure you have all the ducks in a row - new studs with enough thread, nuts to fit, etc - before punching out the existing stud.

In your shoes, I'd take the glue route first because it's easy and doesn't risk creating new problems, then if it didn't work well go either the braze, or stud and nut route.

Another alternative might be plumbers solder if the right flux can be found. If you heated the stud carefully, waiting for the heat to conduct into the joint, you might be able to solder it, before the fork blade got warm enough to damage the paint.

Last edited by FBinNY; 01-04-12 at 12:34 PM.
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Old 01-04-12, 12:34 PM
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If saving the paint is a higher priority , buy a brake booster arch and fit it on the open end
under the bolts.. of course since it rotates , tightening the bolt will be very difficult.

per haps a longer 5 mm instead of 6mm bolt will go all the way thru,
and you can put a nut on the back side.
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Old 01-04-12, 12:44 PM
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JB weld. And I say this as someone that has a torch, a batch of silver, and knows how to use it
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Old 01-04-12, 12:48 PM
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Well I did the paint so I can always redo the paint in that area. I'm just hesitant to take a torch or welder to it because unlike the glue its not something that I can undo. We'll see how things go tonight. I first need to just get the brake off so I can see how bad the problem is. I was at my girlfriends last night and didn't have access to a lot of tools.
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Old 01-04-12, 02:47 PM
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All else you can remove the whole boss from the frame and braze on another one.
the raw pieces are cheap.
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Old 01-05-12, 12:08 AM
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Tapped out the old stud, put in a threaded stud, ground down a nut to fit into the boss, add a washer, some locktite and I got a working cantilever stud. Woot!
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Old 03-03-12, 08:28 PM
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Be interested to see a picture of your repair - I had the same thing installing those same cantis you have. It is not as loose as yours though - the post does not move, just rotates if I try to tighten or undo the bolt.
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Old 05-24-16, 08:39 AM
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I know this is an old thread, but thanks for the confidence to try this. I'm visiting family in the USA and when changing the tires and prepping my 1983 Ross MTB, I noticed the brake was loose and the stud popped off in my hand when investigating. The stud and the weird bracket that it was swaged into appear to be exactly the same.

I tried some epoxy-weld, but it didn't hold up. Unfortunately, the broken-off piece of the stud is still stuck to the bolt with the brake in-between, so I had to try to slip the thing together with the epoxy-weld with the spring still mounted, which may have caused the epoxy to fail. I have a very limited toolset available, otherwise I'd probably tap the backside of the stud and run a small bolt with a lockwasher from the backside.

Instead, I think I'll just buy a screw-in stud and do like the OP. As a bike that I ride a couple times a year, I'm not about to dump a bunch of money into it. I bought it for $5 about ten years ago before I moved out of the area, repacked all the bearings and rode it a couple times with the ancient, crumbling tires as a city bike before leaving, and didn't ride it again until last summer. Rides much nicer with high volume slicks.
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Old 05-24-16, 08:46 AM
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Originally Posted by DiegoFrogs View Post

Instead, I think I'll just buy a screw-in stud and do like the OP. ....
If, as I suspect, you had a stud that was swaged onto a boss that was basically a brazed-on open sided box, this won't be as easy as you expect. First of all the hole is the wrong diameter, and secondly it's not threaded to accept thread-in studs.

You might succeed by drilling out the boss, and mounting the stud with a backing nut if you can find one that fits into the box. With the nut to provide the mechanical support, and some adhesive to keep things from spinning o working loose, you might be able to save the bike, but it's up to you to decide if you want to invest the effort.
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Old 05-24-16, 09:12 AM
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Alternative : drill thru the base so you can thread the whole way through,

so the hole is smaller , to not remove the rest of the threading

and then the Tap [6 x 1 tpmm, I believe] can thread the rest of the inside of the Boss..

that will let you put a nut on the backside and screw a long set screw In .

the set screw has its own hex socket , so as to hold it and tighten ut against that squared off Nut,

And again Hold the set screw While you tighten a 2nd Nut on, that will hold the Brake On..
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Old 05-24-16, 10:40 AM
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Originally Posted by FBinNY View Post
If, as I suspect, you had a stud that was swaged onto a boss that was basically a brazed-on open sided box, this won't be as easy as you expect. First of all the hole is the wrong diameter, and secondly it's not threaded to accept thread-in studs.

You might succeed by drilling out the boss, and mounting the stud with a backing nut if you can find one that fits into the box. With the nut to provide the mechanical support, and some adhesive to keep things from spinning o working loose, you might be able to save the bike, but it's up to you to decide if you want to invest the effort.
Yes, that's exactly it. I haven't measured the hole, but I'll drill it out if necessary. There should be enough 'penetration' to put a (possibly modified) nut on the backside. I have access to a drill and some grinding tools. I'll use some anti rotation washers. At such a low cost solution, I think I'll try it. Outside the motorcycle levers, the bullmoose bars and one of the cranks, there's not much on the bike that's special, but it actually rides kind of fun. Besides, I like projects, and I don't have much else going on for the next two weeks...
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Old 05-24-16, 03:22 PM
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And... It worked!



I went to the LBS and explained what I was looking for. The guy, who I'd never met before, and I went through his bin of junk, and we found a stud that looked good for my application. It turned out to be threaded M8x1.25, which was more coarse than the others, but also longer and it fit exactly in the hole. I went and bought a bunch of regular and nylock nuts, regular washers and lock washers at a hardware store. I had to grind the back of the stud so that it didn't bottom out against the seatstay, and spent a bunch of time grinding a nylock nut to fit inside the "box" that the thing was swaged to, making sure to horribly burn my hands on each iteration of grinding and impatiently checking the fit. I bolted it all back together with an arrangement of washers and lockwashers, and it works fine! The 'modified' nut doesn't rotate inside the box, so it was quite easy to snug everything down. A highly rewarding and recommended project.

I bought a bunch of stuff I didn't need, but if I bought only a couple washers, a couple nuts and the stud, I think it would have been a $2-3 repair.
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Last edited by DiegoFrogs; 05-24-16 at 03:27 PM. Reason: Edited for image rotation and tiny details
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