Okay... GOT IT!
(this may be a long read, but it's good, IMO)
Here's what I started thinking/doing:
@CatchaCuda the pic you sent me seemed familiar as the piece of wood started creeping in this one here too. That told me that it was likely that the rod was a double rod/single action. The "anchor" was the top rod, resting against a very thin and unsupportive piece of wood.
So I ended up doubling down and made myself a little support "bracket" out of scrap wood to allow the tightening of the rod to pull that piece out, so I could find out how deep things went.
Kept tightening until the piece of "support" came out:
That's about all there is, the little piece came off and revealed the style of truss rod.
So I attached the nut and my sacrificial bolt to the truss rod, clamped the sac bolt into the vice and PULLED!
The truss rod came out that far. It wouldn't go further though.
BUT... that really would be unnecessary because I figure out what the fix is and it's dumb easy (sort of).
@RSBBass you honestly nailed it. But I'll tell you why I was not immediately on your side with it and the answer is basically involving how this truss wheel works and where my head was at in the mistake. You were ABSOLUTELY RIGHT though.
- These truss wheels rest on the base of the neck and use that as a point to pull the rod itself. Under there is where I was thinking it would need a washer. Honestly, if the design were the old single rod, that would actually be kinda sorta true because a normal truss nut presses against the wood or metal "support" built into the neck. The wheel being external, I figured if I added a washer that was smaller and fit inside, it wouldn't actually accomplish much because the rod was traveling how it would travel and the washer wasn't making much difference anyway because the base of the neck held tension...
- What is happening HERE is that the truss wheel does use the shoulder of the neck heel to add tension. But being the design it is, it ends up pulling the whole truss outward! That is what knocks the wood out of place. It would stay sort of in place with the wheel holding it in, but would kind of come to a stop and the truss would run out of travel.
THE FIX AND HOW IT WORKS:
That little piece of wood that gets knocked out? It's trash. It's useless. You can toss it. Or glue it in carefully, if you want, but frankly, it's decoration more than function.
What you really need in there is the spacer that would fill the "travel area" and keep the rod from being pulled out of the neck.
On the left is the stock "washer" for the rod, on the right is the spacer. That spacer is actually a piece of a bicycle chain, THE ROLLER. I used to work at a bike shop and snagged a bunch of them from scrap chains to keep as truss rod spacers. They are hardened steel and drastically better than most "washers" because they won't mushroom like this one did under pressure.
I ended up using 2 of those rollers as spacers and they appear to be working fantastically. They fill the gap, the rod tension is borne on those, not the heel of the neck wood, and I can get a mad back-bow in this neck (it still has a wicked front bow naturally, but I'm going to keep torturing it).
This one lives to fight another day.
Okay, so why does that work without an anchor point?
Well, if you've ever had a "golden era" Warwick, you may or may not know that the truss rods in those could be removed without taking the neck apart. They just slid out as a unit. The concept was, once it was seated in place, the truss rod worked fine to add relief by pushing against itself. There was no shoulder or support built into the neck, it was built into the rod.
This is essentially the same design. As you can see, the truss could likely be removed like this without much effort, other than pulling. And the only reason to remove it completely would be if it were snapped, which this one isn't so I'm not going to force the issue.
Point is, if the rod functions, there's no reason to do much more than fill that gap with a nice spacer and make sure the rod is seated as far in the neck as possible.
'Cuda, or anyone else with this issue, the fix can be had with these chain rollers. I'm happy to help anyone out if they need a pair, but you can also go to your local bicycle shop and peruse their scrap chains. I guarantee, if they are anything like my shop used to be, you can bribe them with beer and/or pretzels and they'll hook you up.
So yeah... I think I can put this one to bed at the moment. There are design issues and wood quality issues, but the fix involved is not rocket science and should allow for better performance out of these basses for practically no money and little effort (compared to removing a fingerboard).
Speaking of beer... I deserve one now!
