Cold Setting problem
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?
you didn't say what your procedure was. Did you check to see that the dropouts aren't offset to one direction? I probably wouldn't be comfortable stretching that far on a built-up bike frame.
the good news is that even if you do nothing, you probably will not notice it while riding
I used the Park Tools FFS-2, Frame and Fork Straightener, and I bent the chain stays out. In between each stretch attempt, I checked with calipers to see where I was with the spacing, and then, I checked with the Park Tools FAG-2, Frame Alignment Gage to make sure they we were getting them even.
I realize that I probably won't notice, since I probably rode it for a while with the previous wheel set and didn't notice. My issue is mainly with how the brakes are lining up. One brake is almost hitting at a forty-five degree angle and not traveling far at all, while the other is having to travel too far.
It sounds like the stiffness that the brake bridge adds to the seat stays kept the upper part of the rear triangle from bending symmetrically for some reason. If you had access to an alignment table, you could measure that, but fixing it might not be that easy. You could use something like the park tools fork alignment gauge to check to see where the brake bridge hole is, I guess they don't have one for the rear triangle though. You could add washers to the fork tool. I think you can use the FAG-2 to do this too. Just check the side to side alignment at the brake bridge. Not quite as easy as the dropouts, but you should be able to get an idea.
I think mr hausen is correct about the seatstay needing to move as well. You might try a dummy axle in the dropouts and then run a string from the center of it up to the binder slot to measure from at the bridge. If its off, you can lay the whole thing over on the floor with the dummy axle in place and smash the seatstays the direction they need to go with a two by four a rag and a sledge hammer.