Bass neck, maxed out truss rod, whippy curved neck

[Stephen Faulk]

Hi,

I have a problem with a bass in for repair and it's not my regular thing, need ask about it.
Nice bass, maple body and neck. Owner had it made for him about 15-20 years ago.

The neck is bowed badly and the truss rod is tightened all the way. I have the numbers on the action written in the shop ( I'm not at shop) but it goes from about 2.5 mm at the 5th- 6th fret and then 2.5mm at the 16th and in between is a big fat 3.5 mm scoop. The neck is fairly flexible at this point and I can with moderate pressure push it back straight as it needs to be to not have a bow.

It seems like a job for carbon fiber spars to reinforce the neck. But I want to check to make sure there are no other better options as I'm not a bass specialist and I thought there might be options. I don't look forward to taking the fingerboard off, and routing through the back of the neck to inlay CF is not the most structurally efficient way to use the CF.

My first impulse was to rout out the back of the neck, inlay carbon fiber and then close with a filet of rosewood. the customer is fine with my judgement on aesthetics, but structurally I have doubts about this method. Setting the CF under the fingerboard seems better, but oh my I don't want to take it apart unless I absolutely have to. And I don't know how this will interact with truss rod, or get in its way.

Any bass makers have a word of advice?

]

[Joshua Levin-Epstein]

before doing surgery, you might try un-maxing the truss rod by removing the adjusting nut and inserting some washers.

If you were to remove the fingerboard, the finish touch up would be pretty easy considering the oil finish. I would not go in through the back.

[Mark Swanson]

Yes, if the truss rod has reached he end of its adjustment threads, then adding a few small washers may be all you need to do.

[Stephen Faulk]

I friend told me to back the truss rod off and see if by chance it is "hung up" in the channel somehow and let the neck relax.

If I back out the truss rod will it come all the way out? I don't work on basses so I am kind of flying blind here. What should I expect to be the process?

[Barry Daniels]

Removing the truss rod is unlikely. Most are not made to be removed. As others have said, your best bet is adding thick washers.

[Brian Evans]

Speaking of washers, AN washers have a small OD, just larger than the typical nut, a tight fitting center hole so no sloppy fit and come in two thicknesses - 1/32" and 1/16". This makes them great for shimming and thing like this where space is going to be an issue. I get them from Aircraft Spruce mail order.

[Stephen Faulk]

Ok, so the truss rod has a female Allen socket on the end of it and it can be turned with an Allen wrench and the opposite end is not exposed on the head stock.

What I'm asking is, does the Allen head nut come out? Where do we put the washers? See picture of the end of fingerboard, of the Allen head end of the truss rod. And if the rod is not supposed to be removed then washers are not the fix.

[Peter Wilcox]

You unscrew the truss rod nut (lefty-loosey) all the way and remove it. You may have to remove the neck but it doesn't look like that's necessary. Then you need to find washers that have the same outside diameter as the nut (or whatever will fit in the groove) and an inside diameter that will fit over the threaded end of truss rod where the nut screws on. After putting a few washers in the groove and over the end of the truss rod, screw the truss rod nut back on. This should give you several threads more tightening of the rod, hopefully enough to straighten the neck.

The hard part is finding washers that fit inside the groove and over the rod. I have used lock washers with success, because they have a skinny enough form factor, and are fairly thick for their size.

Also, you may find it easier and less stressful on the truss rod to clamp the neck straight while you reinstall the nut, rather than trying to straighten it by cranking on the nut. Basically put a block on either end of the neck and a thick board between them, then a clamp in the middle of the neck.

[Stephen Faulk]

You unscrew the truss rod nut (lefty-loosey) all the way and remove it. You may have to remove the neck but it doesn't look like that's necessary. Then you need to find washers that have the same outside diameter as the nut (or whatever will fit in the groove) and an inside diameter that will fit over the threaded end of truss rod where the nut screws on. After putting the washers in the groove and over the end of the truss rod, screw the truss rod nut back on. This should give you several threads more tightening of the rod, hopefully enough to straighten the neck.

The hard part is finding washers that fit in the groove and over the rod. I have used lock washers with success, because they have a skinny enough form factor, and are fairly thick for their size.

Ok Thank you that is what I needed to know. If I can't find washers the correct out side diameter I will carefully grind them smaller, but I think it may be possible to find them with some looking.

I don't work on instruments with truss rods usually so I did not want to unpack something that does not pack back in.

[Mark Swanson]

Peter nails it.

[David King]

The worst that can happen is that the nut is galled onto the end of the rod and when you try unscrewing it the far end of the rod unscrews from the anchor. This has happened to me on a couple of Fenders in the past and I had to drill a small hole in the fingerboard in front of the anchor to get the rod back into the hole.

If the nut is galled you can try a drop of oil down through the allen key hole and hopefully were it needs to go.

Actually the worst is that the end of the rod will break off inside the nut right at the end of the threads.

If the fingerboard turns out to be light weight East Indian rosewood I'd consider replacing it with a Macassar ebony one to help stiffen things up.

PM me if you need some washers. I can turn them out in a minute on my lathe and drop them in the mail to you.

[Michael Lewis]

First do no harm: if the rod will not come out (binds at the end of the threads) maybe the answer is not too far from your suggestion of CF bars. If that is the case you can remove the frets, rout slots on both sides of the truss rod leaving some material between the rod and the slots, then fill the slots with CF and filler strips of appropriate wood, and re cut the fret slots in the new filler strips, and fret the neck.

So much depends on what is going on with the rod: is it bottomed out, or is it just really tight?

[Joshua Levin-Epstein]

I think Michael means if the truss rod adjusting nut won't come out. You need to be very sensitive to what the rod and nut are telling you. I've had the truss rod unscrew at the far end (as David describes) and the first inkling I had was the "pop" when it cleared the anchor. That is a very bad sound. This was repaired by removing the large inlay (jazz bass) at the first fret, as well as some wood, putting everything back together and replacing the wood and inlay. I've also seen this repair done on a solid maple neck by removing wood under the nut.

It might be a good idea to contact the builder who may be able to tell you the construction details, rather than doing exploratory surgery.

[David King]

If it's a nice custom bass that has a neck that isn't stiff enough and a truss rod system that doesn't work then I wouldn't hesitate to warm up the fingerboard and try to remove it with a good pallet knife. I did this job to a bass last year and it cost the guy $700 for a new acrylicized ebony board, two 1/8" x 1/2" cf strips that engaged into the back on the fingerboard. He'd had and played the instrument for 20 years. The results were good but the sound changed rather radically, (luckily he thought for the better). The original fingerboard which looked like rosewood turned out to be some kind of walnut and was much to soft to counteract the compression of the truss rod. He could have gotten a very nice new factory bass for his money but a replacement custom would have cost him 4-5 times more.

[Beate Ritzert]

Why would it not be an option to losen the trussrod, let the neck adjust for some days (without string tension, of course) and then straighten it under heat an humidity in a way otherwise similar to the example of Peter Wilcox? Or refret it and use frets with wider tans as far as these are available?

(Yesterday i noticed that the neck of my Gibson EB-11 remains curved after one night without string tension and without tension on the trussrod... looks as it will need such a repair at some time in the future [not now, it is still adjustable - it turned out that it had some back buzz])

[Mark Swanson]

All those suggestions are good ideas, and have their uses. The thing is, if the trussrod on this one is indeed at the end of its threads then it is not working right, and the washers should be added just to make it work...then you take it from there, once you have an operating rod.

[Stephen Faulk]

He has church gigs, the bass owner, over the holidays so he may be using it to get through the next month. The bass is playable, well would not call it playable, it still works enough to play basic stuff. I told him I would do research on the problem and think about how to proceed.
I'm happy to get so much good advice from vetted bass makers.

I'll evaluate it from the truss rod perspective and see where it goes. It may work to clamp a straight piece of lumber to it and re adjust the truss rod with washers, I hope that works. The rod is at the end of it's adjustment. The other day when he brought the bas I was able to triage a 1/4 turn out of the truss rod and that was it. He said it improved a tiny bit.

I've had limited experience with custom electric basses, and despite not being around them a lot the neck still feels very flexible, too flexible. To some degree the neck might have taken a set and I think clamping it to straight hunk of lumber will press that bow out. What remains to be seen over the next several months after the truss rod gets fixed is whether it will hold the whippiness of the neck stable. If not then we'll get back to the carbon fiber option. I kind of like the idea of going through the top of the fingerboard if the board itself is a toughie to knife off.

Despite how exciting it is to talk battle plans, carbon fiber implant surgery will be postponed until the truss rod gets addressed.

He has already signed off on having the washer treatment done, so it's just a matter of finishing the gigs to get the bass back in the shop. He's a very nice guy, he bought a ukulele from me when he brought the bass, and has left a couple more instruments for adjustments in the mean time. He sat down and played a spot of Bach on the uke, which was a nice surprise, then said how much? I sold it to him for a song, literally.HAHA

[Chris Richards]

Just a bit to add, so to speak, on washers, I sometimes use a cut and drilled-out truss rod nut as a spacer behind a truss rod nut since it is the correct size and you can cut it and file to the length that you need... The pictures show a Jazz bass neck the I rebuilt that had been converted to fretless. Mind you from what I've read on this thread I think the neck does need some CF stiffening if it's that flexible, A while ago I was asked to build an extremely slim Strat neck and although it played well when it left my workshop it was never robust enough to keep its shape long term.

[Martin Keith]

If I were in your position, I'd consider making a new neck.

That curly maple is likely the culprit for the 'whippy' neck...IMO it's not really adequately strong for a long skinny bass neck.
It can work on archtop guitars and such, but I've never come across a very curly bass neck that wasn't problematically flexible.

The surgery required to stiffen that neck somewhat and address the truss rod problem may end up comparable in cost or hassle
to the work of making a new neck out of straight, plain maple, with a good 2-way truss rod. Heck, put some carbon in too...why not?

I've added carbon to necks like this before, and the result was stronger, but still more flexible than I would have liked.
IMO it might be throwing good money after bad in this case...

[Greg Martin]

If you cant loosen the truss rod,use a heat blanket to soften the glue then clamp the neck in the opposite direction in which it was bowing maybe .020 shim.reheat it in this posistion let it cool and retry the truss rod. worked for me on 2 of 3 times Ive done this. note your not pulling the fret board( dont over heat) at this time.only if you have to rout in graphite stiffeners.