Focus knobs will not raise lens

I think there is something loose inside that is blocking the rack and pinion from raising the lens all the way up. It will only raise about 1/3 of the way from the bottom. I can barely see a piece of brass that looks like it's the culprit. But I'm not sure how to fully disassemble. The hang up right now is the focus knobs themselves. I don't see a set screw on either. They feel like they will break if I try to force turning them in opposite directions beyond their normal stopping point. Anyone know how do they come off? UPDATE: Was able to remove the focus knob covers using a dental hook tool. They are crazy-glued on originally. Also, that brass tube was supposed to be static and not spin every time the focus knob is turned. It turns out that there is a set screw on either side that holds it. Tighten it up, and the problem is solved. thanks, Mark