I have an early 60's Schwinn Traveler 3 speed that I purchased at a yard sale last summer that has some frame issues. It pulled terribly to one side (so much so that when riding straight, the bars/front wheel are noticably turned to the opposite direction of the pull). I've owned some bikes that pulled to one side a bit, enough to prevent you from riding no-handed, but this is the worst that I've seen.

I checked the frame using the old string and ruler technique (looping a string from one of the rear dropouts, around the headtube then back to the opposite dropout, measuring the difference at the seat tube). It was around 1/2" or more off. I aligned the rear triangle to where it's spot-on when measured, and the spacing is correct. I put the bike back together, took it for a spin, and it still pulls to the same side! The front wheel/bars are still noticably turned to one side whent the bike is going straight. It's better, but still bad.

Is there anything else to check? Could the fork be out of alignment? Is there some other way to measure the frame that may uncover where it is mis-aligned at? I hate to not have this bicycle rideable. It is in great condition. Thank you very much in advance for your replies.