Originally Posted by solostyle

I'm having the same kind of problem. Tonight my friend and I checked out my bike the best we could and it looks like maybe where the cog threads and the lockring reverse threads (on the hub) meet, the cog is not wide enough to come up all the way to the edge of that meeting point. Of course the manufacturer would make sure the lockring and cog were perfectly flush, but if you switch cogs around, the cog may not be the same width.

My problem was different, though. It might be that the cog width doesn't quite match, but the more likely problem is that the lockring reverse threads are stripped at the meeting point of the cog threads. The evidence that suggests this, is that no matter how much we try to tighten the lockring, it doesn't seem to actually tighten. It always feels a little easy to turn. We tried loosening the lockring, however, and it actually felt tighter further out. That's because those threads are not as worn out. Or so we think. So I basically need a new hub and therefore a wheel rebuilding. All transplant probably needs is a new spacer.