Hey guys, I think that I have a 70's era Chicago Schwinn 18 speed road bike. I bought it used and it was painted over so there is no identifying model name. I have pretty much restored the bike and I'm using the original parts that came with it. The problem that I'm having is that the rear wheel rubs against the frame. The whole wheel just shifts out of alignment. This happens when I get up to pedal and it just stays that way until I manually move it back into position. I have checked to see if the skewer was improperly fastened but it was. The outer tire is 27x1 1 1/4. The wheel frame is a Weimann 6x630 27x1.1/4. The frame has a horizontal dropout for the rear wheel. Any help would be appreciated.