It seems like its a kind of controversial topic on here, but im thinking of converting a 90’s steel MTB frame to disc breaks.
The GT Tachyon was build with the weird wheel size of 700d which is pretty close to 650b but it’s almost impossible to find (decent) 27.5 wheels for rim breaks.
So I wanted to lace up some Ryde Andra 30 rimbreak rims to put on, but just now saw that there is a weird looking paint flake-off pretty much at the location where you would weld the bracing if you’d retrofit disc breaks?
(->see picture)
Could it be that the previous owner already tried (and failed miserably) to disc it?
Are there any “clamp on” tabs for disc breaks which would explain those wounds?
Now, since I already have to sand the paint/rust away at those spots to see how damaged the tubing is, I kind got the idea back into my head of a diy disc conversion.
Im okay-ish at TIG but never brazed before.
Getting it done professionally is too expensive and I’ve all ways been fascinated by framebuilding.
The idea would be to get a jig made by a friend who works in metal-fab, tack weld a disc tab and brace and than brazing it.
Can point me to some good resources like the paul brodi videos or has done a disc conversion themselves?
Cheers 🙂
by rabbit_in_space
4 Comments
Don’t. The tubes were not designed for handling the torque in this place.
I’ve brazed on brake bosses and rack mounts to old frames and it isn’t terribly hard but you definitely want to practice a bunch on an old frame before you jump right into it. I use a $30 map torch with a hose that I got off amazon but if you have access to oxy-acetylene that will work better for brazing on something large like a disc tab. I think if you add some tubing as a brace between the seatstay and chainstay it will be strong enough.
One thing I discovered is that silver brazing is a bit easier to get right vs bronze because the metal doesn’t need to be as hot. You’ll have less chance of overheating the tubing that way. Also you might want to try and get a fork that has disc tabs on it already. The forces from disc brakes are larger and asymmetrical and you won’t be able to add any additional bracing.
dont do it bro.. save the money and get a new bike ndown the road
I did this recently, MIG welded a frame that was otherwise brazed construction. I used a 3d printed jig that melted in the process but did the job of aligning things. I used part of an old fork for the tubing to reinforce between the chainstay and seatstay. Super fun project and I highly recommend.
I would never modify a fork, but the back of the frame seems low enough stakes that I went for it with very little welding experience.
Seems like the perfect project to dip your toes in with, and now I’m considering building a frame.