I'm having a very confusing problem, not to mention frustrating.
I have a 1987 Schwinn Voyaguer that, of course, came originally as a 6-speed. A little less than two years ago, I re-built the hub to put an 8-speed on it, and I stretched the frame to 130mm from 126mm.
This week, I built a new wheel set. Because I actually do tour on the bike, I opted for Deore XT hubs, and thusly needed to stretch the rear to 135mm. I'll also say as part of the set-up of the problem that I decided to stay with 27" rims (Sun CR-18) because I wanted to limit impact as much as possible (i.e. changing brakes in someway to accommodate 700c wheels).
Problem: The wheel is offset toward the non-drive side by a few millimeters. I can see it when I eyeball the wheel between the chain stays, and the brakes are off a bit.
I've double, triple, and quadruple checked the dish of the wheel. It's spot on. I was also very thorough with the frame alignment tool. The drive-side dropout is approximately one half of a millimeter off, which I considered not enough to attempt to fix and potentially bend it too far. I evened out the dropouts with dropout alignments tools, so they are square as well.
The problem existed before the new wheel and fresh stretch, but I thought it would be taken care of with all this work.
I keep going over it and over it in my head, but my brain is just not catching what I haven't straightened out. Does anyone have any suggestions?