Originally Posted by bulgie

I once repaired a Burley that cracked at the base of the seat tube. It was kind of a Big Hairy Deal, not economically feasible, did it as a hobby so I didn't mind not getting paid for all the work I put into it. Most qualified pros would have turned down the request, or charged more than the frame is worth.

The problem was , the crack was caused by rust. It had rusted all the way through from the inside. Burley didn't put any vent hole at the bottom bracket, so water that got in had no where to go, just puddled there.

And water will always get in, if the bike is ridden in the rain or carried on a car rack through rain etc. It needs a way out.

No way to know if that's the problem in your case. Pictures are 100% essential as a minimum whenever asking "can this be fixed". They need to be properly focused close-ups with good lighting, from several angles. Look at your photos closely, delete and re-shoot if they're blurry or don't show the crack properly. I only say that because so many of the pics that people upload are useless. Sorry if that seems harsh, but you're asking for help here, so help us help you.

But if rust played a part in your crack, then consider that the other seat tube might be just about as rusted, and just about to crack. So repairing just one crack might only get you a little way down the road before the next crack.

As a general rule, welding a crack in thinwall tubing almost never works, it will just crack again, even if rust-through is not your problem. A proper fix might include doubling up over the cracked area with a sleeve or gusset, and fillet brazing (not welding) which allows the sleeve to be properly "unitized" with the tube. But I'm more skilled at brazing than welding, so that biases my opinion on how to fix it. Maybe a really good welder could do it as well as my proposed brazing repair.

Another good option is shop for a new (used) tandem. Vintage tandems often sell for amazingly low prices. You might even be able to upgrade to a better machine for less than what this repair might cost.

Here's my repair, before and after:




The sleeve is tapered, thick at the bottom, down to vanishingly thin at the top and faired-in with brass, so it disappears when painted. WAY fanicier repair than was needed or justified, but it was "fun" for me. sort of.