MIMF

Guys I need to bounce some ideas.
I made an electric guitar a couple years ago that is all good except, by the luck of the draw, the neck geometry is such that the truss rod needs to be nearly slack to get good relief. The rod is a double action style from LMI with a rectangular steel bar on top (against the FB), rotating rod below. It has shrink tubing over the rotating rod.

There are 2 problems with the slack-ish rod. Most annoying is the rod has sympathetic vibration with the strings which causes strange wolf notes. If I tighten the rod, this goes away, but then it is a buzz-feast with the strings almost on the frets and negative relief. The second issue is that you can hit the back of the neck and it rattles in the slot.
its bad.

The owner is ready for me to fix it, and I've got a couple path's forward that both involve removing the FB. Removing the FB is not trivial since this instrument has some elaborate inlays, but I will deal with that.
Solution 1: Remove the FB, and simply re-glue it with induced relief so that the rod has to be tightened significantly to bring the board flat.
Solution 2: Replace the truss rod with a single action compression rod that is in a tight slot (which I should have done originally )

I strongly prefer replacing the rod with a good compression rod. However, this is significantly more work, and because of the headstock I may need to change the adjustment location to inside the neck PUP cavity. I'm not afraid of filling the existing slot and re-routing for the smaller rod, all the woodwork is no issue, but I'm wondering if it is worth it. Also, the owner has read somewhere that compression rods are bad for tone , so he might prefer the existing rod to be just "fixed".

Advise is welcome, opinions will be tolerated.

I might drill a hole into the truss rod slot, from the back of the neck or through a handy fret marker dot (although you imply you didn't use dots) and inject some non-hardening sealant into the truss rod, and then plug the hole. I've had the same thing happen, and I was able to get away with just tightening the truss rod enough in one direction (pro or negative relief) to get it to stop rattling without making the neck too wonky. A better solution is to dampen the truss rod during install, with the goop or some foam, or whatnot.

I've repaired that problem before by finding a convenient place to drill a hole into the cavity between the round rod and flat bar and injecting a bit of silicone caulk into the space. You ought to be able to pull a fret and drill an angled hole into the cavity. I don't remember what I used to inject the caulk. I normally put the caulk in that location when I install the rod, but on two instruments I forgot. I hope I've learned.

well that's 2 votes for "caulk it".
and we're talking some garden-variety big-box store silicone calking? something wimpy is best i expect.

As Bob suggests, i could put it in under a pulled fret - maybe in 2 locations, splitting the rod length into approximately 3 equal-ish lengths. I have extra SS fretwire from this build to, so that's all good.

Really, is that all it takes? How annoying!! Installation instructions include "Oh, and don't forget to jam some crap into the slot."
i never use this style of rod - well now i know...

I always use the clear silicone caulk for this (the white stuff seems to set hard). Maybe a glue syringe (that plastic thing with the curved conical needle) would be a good way to inject it, or use the standard caulk tube nozzle penetrated with a small drill bit.

My caulk tubes always get hard before I use them up. It doesn’t take much caulk to silence a truss rod.

There's a thin clear silicone used for sealing up car windows that might be an OK choice as it comes in small tubes and doesn't cost an arm and a leg. It's also very runny and would easily run around both rods with the potential for gumming things up.

I had the same problem with a double action rod - even rattled tightend either way when I whacked the neck. Frank Ford to the rescue:

http://www.frets.com/FretsPages/Luthier ... ssrod.html

I injected the diluted rubber cement with a regular hypodermic syringe and a #20 needle inserted beside the truss rod nut, and filled the cavity more or less. Problem solved.

I had this problem once and cut the fingerboard off and inserted a fillet on top of the rod (which was not recommended). I squeezed the fillet in the center to take up any slack in the intentioned rod. Then trimmed it all flush. I had put some silicone caulking in originally but apparently not enough.

There is a real thin silicone caulking for RV roofs (for around AC units etc) that seeps into tight spots. (Probably similar to what Dave mentioned for car windows.) Don't remember the brand. 22ga needles are tiny. This stuff would inject much more easily.

I would try the injection method first. Especially with that inlay work.

What about removing the frets and sanding in the relief ?

Thanks for the replies all around.
Syringes and glue dispensing tips are no problem for me. They are a staple.
I'll look for the right caulk and I think I'm good to go.
The owner will be thrilled, he was prepared for major surgery on his baby.

You could always put '13's on it and tell him it wants to be a Jazz guitar.... Those mediums will induce some relief to the neck, if not to the fingers...

that has been discussed Brian - yes...
but
no

how about plasti-dip?
trying to find something that won't bind up the rotating rod.
remember this is a double acting rod where the whole rod rotates.

The fRank Ford article posted above alls out the diluted rubber cement for two way truss rods. Good enough for Frank, would be good enough for me.

Are you all using silicone or similar to bed your two way (shrink wrap) truss rods when new or only of a buzz develops?

The round part of the rod is usually covered with shrink wrap tubing. I’ve always used clear silicone caulk and never had one bind up on me. If you really want to use something else, you might try a mockup with another rod like the one that’s in that guitar.

I wouldn't worry too much about binding up the truss rod with your additive as long a you don't insert something that dries hard, like epoxy. Assuming you have the truss rod already adjusted to a good action, additional adjustments will be small and incremental. A soft additive like caulk or rubber cement should accommodate this small amount of movement.

Ideally, inserting something that fills but does not adhere would be best. I can't think of anything like that at present.

Edit: what about melted wax?

Melted wax is a neat idea, but I worry that it’s not elastic. After a hot day or an adjustment, it may no longer do what it’s needed to do.

i think i have the perfect stuff already. it's called Flash-Mate - clear gooey stuff that does not really harden or stick well to anything.

BTW, the best possible material for this would be a silicone casting compound. I worked with this stuff years ago. We called it "blue goo".
It is a 2-part material, and results in a nice soft silicone rubber that does not stick to anything. And it is thin enough to inject.
but ... it's expensive and you mix the whole package in one shot so it would be very wasteful. Flash Mate it will be

It's says it's supposed to stick to everything. I'd run a test but stickiness may be just fine in your application as long as the rods don't ever get bound up to the point where they can't slid past each other the mm or two it takes to adjust the neck from one season to the next.

Well, its going to be sticky. The flash-mate i had was solid, so i got some 100% silicone caulking. i _may_ be able to do the work tomorrow. will post pics of the process when i do.
BTW - i still maintain that the casting compound would be the best possible material for this. something that is rubbery, and conformed perfectly to the channel and the rod will absorb all vibrations of the rod. AND it does not adhere to anything so will let the rod rotate and slip in any direction.