I have an old Trek mountain bike with a "Traditional" handlebar stem (Quill stem?) and I've suddenly become unable to adequately tighten the stem to a) remain in line with the wheel and b) stop the handlebars from being pulled clean out of the steering tube.
I've tried taking the stem out of the tube and there was a thin coating of rust over all the surfaces. I cleaned it all off with a wire brush and went inside the steering tube as best I could. This never had any significant effect.
It is not possible to tighten the nut any more yet the "wedge" no longer seems to generate enough friction to grip the forks. What can be causing this and what can I do to fix it?