Usually the hard part is getting the metal to "tin".
Sometimes it isn't clean enough to get a good bond, or the temp isn't right. Too low, the solder doesn't flow fully into the joint and stick. Too hot- the solder flows into- and right out of the other end!!!
Silver brazing is the strongest, (by a lot) but will damage any zink plating due to the higher temps required.
I made my own radiator tanks out of sheet brass, and hose elbows from straight copper tube for my Lola radiator, and soldered them onto the core.
I've also done some re soldering of rad tanks on farm equipment in an emergency. It's much harder to get the solder to stick to the old used tanks, unless you do a super job of cleaning and tinning.
I'd like to hang around the radiator repair shop and pick up some tips some day when I have time.
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer
[This message has been edited by davidpozzi (edited 08-30-2001).]