Does the neck cause a truss rod to turn?

[MirandM]

I would try to eliminate certain invisible problems first. Starting with de-tensioning the neck completely, remove the strings and release the truss rod tension.
Leave the guitar like that for a week and then check the natural convex arc of the neck.
If that is correct, then check the neck pocket and fixings for any problems, play or whatever may occur.
If that is correct too, then restring the neck with two outer strings bringing them to the correct tension slowly and equally (not one and then the other), The neck should be near to straight now, without any rod tensioning
Thereafter tension the middle stings and at the same time adjust the rod step by step. This way you get an evenly tensioned neck. Leave the guitar rest another week and only then adjust the final arc with the rodd.
After that check if your problem still exists.
I know it sounds silly but sometimes it's well worth the trouble of redoing a basic setup from the beginning, much like reinstalling a pc if it doesn't work right for no obvious reason.

 

[MirandM]

...
This is why I avoid buying basses with the truss rod at the bottom of the neck instead of the headstock.

Weird, to me it makes no difference where the nut's located as it tensions the rod over it's complete length, which is exactly what it's supposed to do. As far as I know the difference is mostly estethical with the exception of a very thin neck at the head which would leave little room for the nut or debilitate the headstock.
Even with headless basses I've seen it both ways.

 

[Coke Kane]

Weird, to me it makes no difference where the nut's located as it tensions the rod over it's complete length, which is exactly what it's supposed to do. As far as I know the difference is mostly estethical with the exception of a very thin neck at the head which would leave little room for the nut or debilitate the headstock.
Even with headless basses I've seen it both ways.

Oh, I meant, that it would be a hassle to remove the pickguard and/or neck to access the truss rod if it was located at the bottom of the neck. It's much easier to loosen the strings to access the truss rod located at the headstock.

 

[MirandM]

There's a thread here Adjust truss rod on CIJ Fender Classic 70's P-bass that discusses your point. While this is true with some guitars that have pickguards my yamaha bass has no pickguard and the nut at the bottom like this

There's also a different nut to avoid having to remove the pickguard, like here: Metal peice sticking out on bottom?

Either way it is preferable not to loosen the strings when adjusting the nut which is why the advice is always to turn the nut no more than a quarter turn. It's like adjusting your car's tire pressure, you don't remove the wheel to do that as it is more accurate to do it with the car's weight on it.

 

[MirandM]

... It's much easier to loosen the strings to access the truss rod located at the headstock.

Btw, is that your normal way of adjusting the rod tension? Because if it is, it would very likely explain the origin of your problem, flip-flopping the neck tension.
As most of the replies in this thread indicate, having to adjust the rod tension is not a frequent thing to do. I have some 15+ basses but hardly ever need to adjust them, being correctly setup like I explained earlier.
Drastic environmental changes (like also said) may have their influence as basses are mostly made of wood, a natural fibre that needs to be treated as such, with patience. For example, when I receive a new bass I never set it up the same day I receive it. I leave it for at least 4-5 days in my room to acclimatize before even picking it up.
When I was like 10 years old one of our neighbors was a profesional violin painter, well it's not painting really, more like oiling. He had been working for like 12 months on a violin to sound exactly like a stradivarius, it's all in the oil and patience he said. I learned a lot about wood and it's treatment from that guy.

 

[Turnaround]

Weird, to me it makes no difference where the nut's located as it tensions the rod over it's complete length, which is exactly what it's supposed to do. As far as I know the difference is mostly estethical with the exception of a very thin neck at the head which would leave little room for the nut or debilitate the headstock.

It actually does make a difference. The profile of the relief curve is different depending on whether the adjustment is at the headstock or the butt end. The more even curve occurs when the adjustment is at the butt. But the headstock adjustment is more convenient generally unless there's an access channel in the body or a spoke-wheel adjuster.

 

[MirandM]

It actually does make a difference. The profile of the relief curve is different depending on whether the adjustment is at the headstock or the butt end. The more even curve occurs when the adjustment is at the butt. But the headstock adjustment is more convenient generally unless there's an access channel in the body or a spoke-wheel adjuster.

Come to think of it you may be right, probably because of the thickness of the wood at the butt which makes for a more evenly distributed force. Seen from a mechanical viewpoint the force resistance of the neck at the butt is higher than at the head which might explain the different curve.

 

[SkyWinders]

I'm fussy about how my bass is set up. I probably adjust the truss on all of my basses About twice a month.

Well, maybe not need adjustment more often, but one might want to do it more frequently. I adjust the truss rod on all my basses 2 or three times a month. I admit I am very fussy about my setups, so if the neck moves a couple of thousandths I feel it and adjust it.
To respond to the OP's questions, the neck does not cause the truss rod to move, the neck changes in response to changes in humidity. Are you always having to tighten the truss rod or do you sometimes have to loosen it to keep the board flat?

I mean, I did eat a bowl of stupid for breakfast that day