Capo the 1st fret and fret the 22nd fret.
Is there any clearance between the 7th fret and the bottom of the 1st string?
If there is some clearance measure that clearance between the 7th fret and string.

Then "loosen" the truss rod 1/4 turn and measure the 7th fret clearance,again.
If the clearance is greater then you know that looser is more bow.

If the 7th fret is contacted after capoing 1 and fretting 22 measure the nearest next fret that has some clearance for a reference.

I like a 7th fret clearance of .015".

Thanks for the neck relief info.  As I noted, I'm familiar with loosening/tightening the adjustment nut on a standard truss rod.  The problem is that this banjo uses a different type of rod adjustment (maybe also used on a few 1960-70 Gretsch guitars?).  It's an indirect gearbox linkage, rather than a direct nut adjustment.  That's why I'm unsure which way to turn the adjustment lug, and how far to turn it.  SETH

Has the bow gone negative leaving the string touching the 7th fret when capoed at 1 and fretted at 22.
Is there any clearance?

Seth,
Counter clockwise, & being a gear box, you will need to do several turns to see any results.
On my home page photos is a Baldwin/ODE truss rod & gear box, , Burnes Gearbox.
And what Steve said.

Tom

Thanks for the gearbox information, those were the missing pieces I needed!  

To answer your question, the concave neck bow resulted in almost no clearance of the frets from about the 7th-8th fret and higher (towards the banjo head) when fretting a chord.  When I played, I was getting less and less volume and couldn't figure out why.  Then I saw that the fretted strings were basically laying on the higher frets, damping any vibration.  No wonder I wasn't getting much volume! 

I believe this banjo always had a flat fretboard (no neck relief), so that's what I'm initially shooting for.  I do like a little bit of neck relief in my guitars, so I might give that a try, too.  Now that I know which way to turn the lug, I'm more confident about adjusting that truss rod.  SETH

Tom, I finally figured out how to access your photos of the Baldwin/Ode gearbox truss rod adjustment gizmo, and it's pretty much what I had assumed was the case -- a worm gear.  I'm not sure why Ode/Baldwin didn't go with the more traditional (and much simpler) "acorn nut" direct adjustment in the peghead, but as they say, "it is what it is"!  Thanks again for sharing the info and the interesting pics.  SETH  

I happened to see this on Richie Dotson’s site today.

banjomart.com/product/vintage-...L6HEEAMN6

Richie is REAL proud of that , I make them & give them away.
Seth,
The old ODE company did an acorn nut at the heel just under the fingerboard but you needed to remove the neck to adjust it, & that's how I install truss rods when I make a repo neck. It would be eaiser in the peghead but there is ODE inlays in the way & I have seen at least one repo neck with the nut & cover in the peghead.

Tom

When I purchased my Baldwin ODE D in the 1970's, it came with the T tool but was actually a tube with two sides squeezed/flattened in so it would drive the axel in the gear box.

When I bought my Baldwin/ODE around 1970, it didn't come with a truss rod adjustment tool.  I've juryrigged one as banjonz noted, by squeezing a metal tube (actually an old nut driver, I think) into an oval that would engage the lug on the gearbox.  It's not perfect, but the price was right! 

I can see why Baldwin would want to go with the Burns gearbox instead of the acorn nut at the end of the fretboard, which required removing the neck to access the nut.  But it still seems to me that the gearbox was an overly complicated (and probably expensive, too) way to solve the access problem.  But it is what it is!  SETH

I have heard of but not seen or experenced the broken gear box as of today & hope I never do. That would be an expensive repair.