P-Bass truss rod adjustment

[auditron501]

I have a stock '76 Precision Bass, maple neck. The neck is bowed very slightly. I can tighten the truss rod and get it exactly how I want it, plays very nice. However, over the course of 3-4 weeks it will eventually return back to where it was before the adjustment, slightly bowed. I can make the adjustment again, but it will become bowed again in a few weeks. I have repeated this procedure probably 5-6 times in the 10 years I've owned this bass. I am concerned that the repeated tightening of the truss rod will eventually max out or strip the threads. Why does it keep becoming bowed? Is it possible that the nut is slipping or partially stripped? Any suggestions?

 

[Turnaround]

It's not likely that the nut is slipping nor stripped. It is far more likely that the wood under the nut is compressing thus requiring further tightening of the nut.

Running out of threads on the truss rod is not a concern because you can always add a washer or two to put the nut back onto a good threaded part of the rod. And the wood will not compress forever. But it could do other damage under compression, like crack the fretboard.

What strings are you using? What gauge? It may be that the neck cannot handle the tension of the strings. If you remove the strings and completely slack the truss rod, is the neck then entirely flat, or is it up-bowed?

 

[auditron501]

Thanks Richard. I just looked at it. It has the flathead cross X type of nut. It is recessed about an eighth of an inch beyond flush with the heel of the neck, so compression of the wood sounds logical. I read somewhere that the nut should be flush with the heel, correct? I'm thinking I need to add a spacer or two. I see that StewMac has them. It is strung with Fender Medium flatwounds .055 - .105. I've never taken the strings off and loosened the nut, so not sure if it'll bow unstrung. Might try that since I'll probably be removing the nut at some point.

 

[Turnaround]

Thanks Richard. I just looked at it. It has the flathead cross X type of nut. It is recessed about an eighth of an inch beyond flush with the heel of the neck, so compression of the wood sounds logical. I read somewhere that the nut should be flush with the heel, correct? I'm thinking I need to add a spacer or two. I see that StewMac has them. It is strung with Fender Medium flatwounds .055 - .105. I've never taken the strings off and loosened the nut, so not sure if it'll bow unstrung. Might try that since I'll probably be removing the nut at some point.

It's worth knowing if the neck is flat without tension from the strings and truss rod - it's a good indication of the "health" of your neck.
Flatwound string have appreciably more tension than the same gauge of roundwounds, so your strings may be contributing to the problem. You might try some light gauge flatwounds or some that have notably less tension such as the Thomastik Infeld Jazz Flats. And I would get yourself a spacer for the nut - it sounds like it has compressed the wood significantly and you may soon run out of threads on the truss rod.

 

[hotbass57]

I found the Fender flats were fairly high tension. I have TI's, Labella low Tension Flats and EB Cobalt flats on my basses. The TI's are the least tension followed by the labella then the EB Cobalt flats. I have the labella on my pbass and they sound so good very easy to play great tone I get compliments all the time. I agree what Richard says I would def try less tension flats.

 

[auditron501]

I appreciate your knowledge and experience responding to my questions. All good advice. I finally got around to removing the neck. With no string tension and the nut loosened, the neck remained pretty straight. I think I'm good there. I added some spacers to compensate for the wood compression which definitely helped. I agree that the high string tension is probably the source of my original problem, but I kept the Fender flatwounds on it as I really like the feel and sound. Not sure I'd be happy with lighter guages, but I may go that route at some point. As of now the neck is holding steady, action is fine and it sounds good.