boneshaker78

I found a bolt that fit into an old 2003 Jamis Coda Comp frame for the brake bosses and it was a perfect fit. I checked it with a die and it appears to be M6 x 1.0. I looked for brake bosses this size and I’m having a hard time. Anyone know of a place to order these?

grumpus

Bosses

boneshaker78

These are screw in type boss studs, not welded/brazed on.

grumpus

Ah, you mean the inserts that are always M8 or M10 - has someone cut this off so only the thread for the pivot bolt remains? Can you drill and tap it for M8? At a pinch cut the pivot from a scrap frame (or order some from Ceeway) and use a high tensile M6 bolt and Loctite to hold it together.

boneshaker78

No, I really don’t feel that these have been tampered with in anyway. I think they are stock from Jamis. I’ve seen threads in other forums discussing this rare size. Thanks for your help!

boneshaker78

Here’s a link I found regarding the size… https://www.retrobike.co.uk/threads/...bosses.239958/

Dan Burkhart 

They are not always m8 or m10 . In rare cases they are indeed m6 and sometimes even 5/16 x 18.

grumpus

Well I never ... but now I do. :-)

mtbikerjohn 

Probably not with a 2003 Jamis though....

mtbikerjohn 

Try contacting Jamis..That is new enough to the more modern standard.. M8, and sometimes,M10 threads

mtbikerjohn 

The internal threads for canti bosses are usually M6 threads. the threads that screw into frame or fork bosses could be m8 0r m10 on that Jamis

Bill Kapaun

If you found an old rim on the side of the road, would you look for a car to fit it?
I think your approach is backwards.
Get readily available bosses and bolts to fit them.

sweeks

A number of years ago, I replaced the brake pivots/bosses on a commuter bike with titanium ones. There were at least two thread pitches available for the same diameter. I removed one of them and measured the pitch so I knew which ones to order. Now it seems there are different diameters as well... what a nightmare!

boneshaker78

I'm starting to think these bosses, or whatever they are called, attached to the frame are replacements for the originals. I really have no idea, but it looks a little funny because the frame is more of a raw steel look and the bosses are a true chrome.

Andrew R Stewart 

The imaged bosses sure look like common ones but have has the smooth post section removed, cut off. As in these were a one piece type. machined on a lathe and the spring tab plate brazed on. The smooth post section can break off from some impact, but both on the same frame makes me wonder if this frame had them cut off on purpose.

IIRC Problem Solvers (a brand of Quality Bicycle Products) use to offer a repair kit that had a section of tube to replace the broken off and missing portion. The bosses base would be filed square so the replacement would stand perpendicular. A really long M6 bolt sandwiched the replacement tube, the canti arm and the base together. I have installed about a half dozen of these kits, might still have one in my stash. Andy

boneshaker78

You’re so helpful Andrew! Thanks for the reply. That would make sense and maybe that’s exactly what happened here. Rather sad to find this out. ☹️

boneshaker78

Is this it? https://problemsolversbike.com/files...epair_inst.pdf

boneshaker78

The right side is shorter than the left and I believe they were cut off given this evidence. Thanks for the help everyone! I guess I’ll try this Problem Solver solution. Hopefully this will help someone else someday too.

Andrew R Stewart 

Brian- I don't have the kit I thought I had. Work might have one but not two. I will still look on Monday.

I did the next best thing and took some measurements. The OD of a canti post runs between .3110" to .3130", or about what a 5/16" tube would have. The ID needs to clear a M6 bolt. That's about .236". A wall of .035" gives an ID about .243". So, a 5/16" x .035 tube, cut to a specific length with a properly long M6 bolt and nice washer gets one this kit. Cut and square off the tube's ends a slight bit longer than the canti post was (about .646") and file to fit the actual canti arm. Speedy Metals 5/16" OD x 0.243" ID x .035" Wall Other Steel Round Tube Is a source for this tube. Andy

boneshaker78

Wow! Thanks Andy! You saved me from so much headache trying to figure all of that out. Much appreciated 😊

grumpus

The bearing surface is 8mm, the thread is M6x1.0 - if you don't want to hack the relevant bits off a scrap frame I'm sure you can find someone to turn a bit of round bar, drill/thread it, and cut it to length, which is about 16.5mm; a little longer won't hurt, but shorter and the brake will bind. You should use a good grade of screw, as long as will thread in without bottoming, to hold it together - a brake booster is probably a good idea too, and Loctite wouldn't hurt.

boneshaker78

Does anyone know if other issues could arise from repairing the brake studs in this manner? Would it create the potential for the brakes to squeal excessively? Would the braking power be the same as if the studs weren’t cut off? I might consider a brake booster… thanks grumpus.

Andrew R Stewart 

The best repair is of course a boss/base replacement. This would require some chrome removal and the skills/tools to do such. The repair kit I suggested is the make do method. Doing this make do would want periodic checking for the new canti arm sleeve/tube coming loose, the bolt's not staying tight. A brake booster plate would certainly help stabilize the repair.

As to "power" I would say that this goal is pretty far down the list of needs at this point. That's what the front brake is for. Andy

grumpus

If you don;t use a brake booster there will probably be more flex than the original setup, which will be more likely to cause squeal, but you compensate for that by toeing in a little further. Excessive flex if the touching faces aren't flat and clamped firmly together could eventually cause fatigue failure - filing the faces, using a good grade of screw and making sure it's properly tightened should prevent this. As Andrew R Stewart wrote, you're not looking for ultimate power from a back brake anyway.
An alternative repair that occurred to me is to use a M6 threaded stud in place of a screw - that could be silver soldered in place along with the 8 mm section, then just use nyloc nuts to secure the brake arms. The silver soldering would require very good joint cleanliness, which might be hard to achieve inside the existing threaded part.

Krov9

I do in fact have a frame with M6 threaded bosses/mounts for canti brake studs/posts (not sure about the terminology). The bike is French, 70's and from an unidentified manufacturer so I guess I shouldn't be surprised to encounter obscure standards

From what I've gathered while trying to hunt down said posts/studs is that M6 were used in a number of not so recent suspension forks from.RockShox & Magura, as well as by Cannondale at some point.

This is a valuable source, especially for those in the old continent https://brake-stuff.de/en/canti-stud...pring-retainer

As for my bosses, they are actually just bent pieces of steel plate with M6 nuts welded inside, so the threading will be so short I doubt the above mentioned parts would thread in tightly enough. I'm considering getting some M8 nuts welded there in place of the old M6 ones, since they would be hidden from sight