I can't get a 70's Jazz neck to bow either direction, even with the bullet truss rod nut removed and the neck off the bass. I've been going crazy trying to lower the action, and I finally realized that I can barely even backbow it by hand. Could the rod be frozen or locked in some way? I can tighten and loosen the nut at will. Could it be the top of the trussrod is locked somehow? It seems that if it freed up, the neck should bow both directions. It's solid, and won't bow either way. I was getting ready to try the backbow clamp trick, but no point if I can't even budge it backwards by (gently) holding the ends and pushing the middle with my knee. Off the bass, nut removed, the neck is almost dead straight. Put it on the bass, and the strings bow it forward a little, but not crazy like it should with no nut on it. Could the metal ring right at the top of the rod be stuck to the rod freezing it in place? What would be the best way to un-stick that, if that's the issue? This seems to be an odd one.