first off, I hope you are using a solder clevis, not a threaded clevis. The rod just needs to be scrubbed with steel wool and then cleaned with lacquer thinner. I usually clean the clevis with thinner too. Are you using the silver solder from Great Planes, etc that comes with acid flux? If you are doing all this and it still wont take, you might be getting it too hot. I use a mini-torch attachment, a pencil like tool that attaches to a propane tank with a hose, but I have not seen them for sale recently, unfortunately. If you are using a torch that's too big, try a soldering iron.

Peter