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I have this fretless bass on the bench for a complete setup. The new owner hated a very noticeable shim in the neck joint.

The previous owner shimmed it in an effort to lower the action. But, the reason for the insanely high action was that the neck relief needed adjustment. Someone stripped the truss rod key hole. The key just spun in it.

After careful consideration, I decided to try to tap the 5mm hole, with a 1/4"-20 tap. There was a distinct possibility that the truss rod needs replacing, but I advised against it. The way they had the fretboard installed and the fact that this bass is inexpensive, just didn't make it worth replacing.

I made a tool with the tap, so I could get it into the truss rod. This was a total crapshoot. I started tapping, then realized that the truss rod may have started adjusting. Sure enough, the neck relief had adjusted to proper relief. I was going to solder in a cut off screw with a cross cut into it so a screwdriver could be used to to adjust it in the future. But. I left well enough alone.

The strings were 7/32" high at 12. Now they're as low as 2/32 without a buzz. I adjusted to 5/64".

Nice Diane.
Genius and lucky!!!!

Fortune favors the bold! That's awesome

It is occasionally possible (okay, Ive done it once) to pull out a truss rod. I was able to do it on a Harmony Sovereign and slide in a new double-acting rod to replace the single-acting rod it came with.
I think I needed to shave just a bit around the access hole, then I pulled and it came out.
To get the new one in, I had to make a rectangular sort-of broach the dimensions of the new truss rod cross section and clean up the full length of the hole.

This truss rod is firmly in place. No way to pull it out, I wish I could.