Putting disc brake mounts on a vintage mountain bike

[chunkolini]

Hoi Hoi
I ride an antique Kona Kileuea as my commuter bike. This poor bike has a 20 mile round trip each day on tiny country lanes lubricated with a nice slurry of grit and cow poop, luverly stuff, a very effective grinding paste.
the frame is made of 'Columbus somethingorother' tubing. A lovely thing, very light and springy, and makes that classic old school 'Ting' if you flick the main tubes with a finger nail.

Plan A is to braze the disc mounts onto the rear stays, these are already brazed into socket style dropouts. The problem is these ancient frames were not built for the type of loading applied by disc brakes and I dont want to bugger it up as it is A, a nice thing and B, possibly quite valuable, at leat £250.00 even at 13 years old. I think a curved gusset liknking the two stays either side of the mount would spread the load. I wont be stunting the bike, just putting on high mileages in chronic conditions. Some tragic folk would argue that I am ruining a classic, I have been told off for fitting a suspension fork onto it, cobblers to them I just dont want to knacker it up.

Has anybody got any opinions/experience on this business. MTBPete where are you?

Chunko'.

 

[andypocock]

Funny you should post Chunko as I've just spent a couple of hours messing about with a bike frame thanks to your inspiration

Stage 1:

I've no idea what stage 2 is yet but it looks like it is going to involve some pipe and longer forks.

Insane project but more fun than practicing welding on bits of scrap.

Andy

The disk brake - How about a caliper mount on the spindle and an anti-torque arm secured with a clamp around the frame? Think anti-dive braking without the anti dive. No alterations to the bike at all.

 

[Glyn]

Recently did this to my old steel framed bike. I tigged the mount on then brazed a tube from the seat stay, at the highest point of the brake mount, to the chain stay. I made the mount out of an old car disc pad, mounted the wheel in the frame, put the disc brake on, clamped the brake lever and tacked it in place. Took brake and wheel off and welded it up. I also ground the old canti bosses off and brazed some hose guides on. Works a treat.

 

[chunkolini]

Glyn, that is pretty much how I did it on a slutty chopper I built a few years back, weld/braze the mount after clamping the disc caliper onto the disc, using anold car brake pad has pure class, would look good with some of the pad material left on it.
What type of frame did you do it too? old dodgy bikes have so much excess material there is nowt to worry about, this one is a fragile beaut. I know that I have to do it anyway...........

Now look Andy, this is not big or clever OK. The next bit is top secret.

But that looks great, you have thought about it and done your own thing, not copied every other sucker ''Hats off'' free pint of cider. A work of genius, you have raised the back end, which when tipped up lifts the front end, giving room to stretch the forks without giving stupid tippy handling. I hope the chain stays are not butt welded, if they are weld some crappy bits of plate either side, and leave them looking like a sore thumb. Forks, get some quality CroMo tubing if you are a precious So and So, otherwise get some ERW exhaust tubing that will be a sloppy fit just above the brake bosses on the donor fork, leave a couple of metric inches of fork inside the tubes and badly lap weld them on. Make some crap wheel mounts out of 3mm plate/strip. Jack the 'bike' up till it looks about right and spot weld them on, make it good and long. Fit the wheels. If the forks drop over to the side violently whip the dropouts off and move them up the fork a few inches and try again, if they flip gently that should do the job, steerable but not a killer.

(This bit is even more top secret To brace the forks for downhill racing, ram another stem up the bottom, then weld bits of tube from the bottom stem to the bottom of the fork legs, and figure out how to brace the bottom stem to the top one, bolts and bits of chewing gum will work, result? one unbreakable fork. If you are a gurl, gusset the head tube as this is the weakest link. But bear in mind, on a normal bike the forces are trying to tear the headtube off by pulling the fork down to the back of the bike, on a chopper they are pushing upwards. When this is done google search 'Klunker classic' contact Charlie Hobbs and write a will. You might as well give all you posessions away as your family will disown you anyway.
Oh, and what is that crappy old motor in you garage? It would do well in the Klunker classic. I am not a car head, but my first thought was a vintage Porsche. Give you a tenner for it. Now Andy, your mission is to kill anybody who read the top secret bits of the thread. Sorry to your family, but a tobacco baron can make a great husband.

Chunko'.

 

[Glyn]

I did it to a fantastic 631 steel frame, the best handling, comfortable frame I've ever owned. I just got so sick of replacing rims, they don't last a year with rim brakes. I'm made up with the bike now, Ive got much more expensive bikes (Cannondale, specialized) but for sheer riding pleasure I don't think you can beat steel. But the best thing about it is you can repair it easy! Why not get an old frame off the scrap man and have a go? you only need the rear end. Bear in mind though, your frame will be a lot thinner than a cheap bike. When I was removing the cable guides off the top tube, I got a careless and the braze haddn't melted properly and I made a small hole through twisting too soon. Just tigged it up though, no problem.

 

[Glyn]

And Porsche in Andy's garage? GB badge on the back? I suspect an E Type.

 

[s7acker]

First proper post from me and I get to do my 'bike nerd thing'!

Back in a previous life I used to build frames for Orange (the mountain bike people - not the phone company) when they still custom made every frame in the factory in Penrith. If I remember correctly, the 96/97 Kona Kilauea was built from a Columbus Cyber Nivacrom tubeset. The Cyber tubeset was amazingly light for a double butted set and it managed this through the complex post weld heat treating process it went through at the factory which meant that thinner wall tubing could be used.

We were using Tange Prestige tubesets that as a set, were much heavier but pretty much indestructible and didn't need to be heat treated after building.

The Cyber top and down tubes were about the same weight as the Prestige which meant that much of the weight saving came from the super thin, flexible seatstays/chainstays.

That's a long winded way of saying - I'm not sure that welding a disc brake boss to the seatstay of a frame made from Columbus Cyber tubing is going to end well! Especially on a frame that relies on heat treating for its' strength.

I've got a lovely 3 speed prototype Sturmey MTB coaster brake hub you can have if you want that?!

 

[chunkolini]

Ha ha S7acker, Fantastic stuff!! I new you were out there.10/10 that is the kind of info I am after. I was thinking of brazing it rather than welding it, but that is still a fairly seriously job with a lot of heat. The other option is to have a Magura rim brake, at least they dont clog up in the dirt. I'd prefer a disc brake but it is a great frame....
Your call. That hub brake sounds cool though for my shopping bike. typical commute, 10 miles each way, 2x1/7 hills each way lush Wye Valley views.

Glyn, after posting my first rant I had another look and thought E type? but haven't they all rusted away?. Nooo sexiest car ever made, and they did 150mph. Mind I saw one once near Coventry towing a caravan!!!!! a powder blue one mind. Shocking.

Chunko'.

 

[andypocock]

Chunko

I've got no idea what a chain stay is but I don't think anything is a simple butt joint.

Thanks for the mission notes. I'll eat the top secret stuff now that I've read it.

I'll update when I next get a couple of hours off.

Andy

PS: The Porsche is an E Type as Glyn suspected

 

[zzr1200]

Nice Jag....

 

[dutchman]

Chunko, can't you sort of sleeve the part where you want to fix the connections for the disk brake claws? I mean wrap an extra piece of metal around the frame/ tube, solder this sleeve in place and have the mounts for the brake calipers tigged or brazed on the sleeve in advance?

 

[andypocock]

Rather than hyjack this thread completely:

http://www.mig-welding.co.uk/forum/showthread.php?p=117917#post117917

 

[chunkolini]

andypocock, another one bites the dust. Welcome aboard.
Chunko.
re the Kona, I will stick with rim brakes, the frame is 13 years old and to nice risk discombobulating it.

Chunko'.

 

[breezer]

mmmmmm Kileuea loverly bike, what do you think to it with the sussy forks?

Got a Breezer frame I built up about 12 years ago, fantastic thing to ride as is any high end steel bike. I have Kona p2 forks in there and I love em, just after building it up though I swapped over a pair of Rock Shox judys I had onto it and hated it, the front end was far too heavy and it became somewhat blundersome, where the P2's used to skip over obstacles like a spring lamb.