by Paul_C » Thu Nov 10, 2022 8:34 am
Nothing's broken if it's just fallen off, it's just that you've kept loosening it until it reached the end of the thread.
Normally a neck will start straight and begin to bow forwards as the strings are tightened up to pitch. If the neck bows too much you tighten the truss rod to straighten it out.
However, sometimes the neck bows the other way, either because of the ambient conditions it's in or because it's wood, and wood does strange things sometimes.
A lot of modern necks come with a double-action truss rod so if the neck is too straight or has a back-bend it can be rectified by adjusting the rod to make the neck bend in the direction it would normally do under string tension.
So, assuming your neck has been bowing backwards and you've been loosening the truss rod to compensate for that I don't imagine the truss rod has been under tension for quite a while as the nut should be loose long before it falls off the end of the rod.
To test this out you could put the nut back on and begin to tighten while looking along the neck and see what point moving the nut begins to make a difference.
If the strings are on and tuned up and the neck is bowing backwards then the simple solution is to put some heavier strings on which will increase the tension and give the truss rod something to do.
It's also possible to bend the neck forwards and apply some heat to "fix" it into a new shape, but that often only works for a while if the wood is determined to bend the other way, so the only thing left at that point is to replace the neck or carry out some major surgery - the first step could be to bend the neck back slightly using the truss rod and then level the frets while it's bent so there's room for adjustment once the truss rod is released.