How Involved is Replacing a Truss Rod?

[ElRay]

I have an opportunity to buy a Classical Guitar that has been on my "Wish List" for a while for nearly free.  The issue is that the truss-rod will only tighten and the neck has a slight back-bow. I had a steel-string acoustic that had the same problem, and that just took some patience, penetrating oil and a tight fitting Allen Key.

If the truss rod truly needs replacing, how involved is replacing it?

[Bizman62]

Oh wow! Replacing a truss rod can be a nightmare or then not. It has been done, there's evidence on this forum.

A lot depends on the design: Is it a dual action or a single action rod?

A single action rod has a lump at the other end preventing the rod from turning and obviously that anchor is much wider than the channel. Some dual action rods also have a cube formed spacer at either end. But many dual action rods starting from the cheapest ones are at their widest at the adjusting nut end so widening the channel at that end should allow for pulling the rod out. Should...

However, since you say it tightens only it very much sounds like a single action rod. Heavier gauge strings may help. If that's not an option or doesn't do the trick well enough, removing the fretboard and replacing the rod to a lighter one might be doable. But it won't be near as easy as oiling and choosing the right Allen Key.

[Crusader]

I was wondering if the Allen key is stripped but if it tightens up then it indicates that it is not. Try just loosening and leave it, or tighten the strings, or as Bizman suggested instal heavier gauge strings

[mistermikev]

I don't think I'd spend a lot of money on it.  truss rod replacement would depend on the builder.  I know there are guys who build such that the rod will slide right out... but myself: I buy an expensive rod and purposely make it such that it will never move.  Just two dif takes.  further the issue is going to be finding a suitable replacement rod assuming you can get it out.  it'd have to be the right dimensions and that is not guaranteed to be easy.  Some guys use custom length rods.  most rods are 1/4" wide and 3/8" depth if it's a two piece but even that - the dimensions might vary enough that your rod is rattling around in there.

that said... it's not clear reading your post if this is a two way rod or perhaps a one way that just only loosens so far.  I'm guessing one way but either way... the wood wants what the wood wants and you could try to bind it to something straight (or even reverse curve) and heat/steam it but IME that has about a 30% chance at working... bending it will def happen but bending it straight and to a specific dimension - pretty unlikely to pull that off.  Even assuming you do pull that off... I've done it to a guitar once and a month later it just returned right back to where it was.  heating the fretboard while it's bound straight might loosen the glue bond and allow it to re-attach in a way that straightens the neck... but it also might destroy the integrity of the glue and open up all sorts of other problems.  assuming you make it through all that and straighten the neck you are likely going to need fret work.

my gut says that when you've got "wild wood" it's just not worth it to fight it... but ymmv.

 

hope something there helps make your decision easier.

[ElRay]

1 hour ago, mistermikev said:

... it's not clear reading your post if this is a two way rod or perhaps a one way that just only loosens so far …

As best as I can tell (at this point) is that it's a one-way truss-rod that can be tightened, but something is preventing it from being loosened.

I'm waiting on clarification to see if the owner really means, "The Truss rod is as loose as it can be, but the neck still has a back-bow" -- That would be a different fish to fry.

[Bizman62]

3 minutes ago, ElRay said:

As best as I can tell (at this point) is that it's a one-way truss-rod that can be tightened, but something is preventing it from being loosened.

If that's the point, loosening it and then banging the neck might do the trick unless the rod has rusted in place. In such a situation some rust removing oil might loosen the rod but although stuff like WD-40 can be used for cleaning wood it's also known for effectively removing glue residues. In the worst case such an oil could delaminate the fingerboard and impregnate the wood against regluing.

[mistermikev]

9 minutes ago, ElRay said:

As best as I can tell (at this point) is that it's a one-way truss-rod that can be tightened, but something is preventing it from being loosened.

I'm waiting on clarification to see if the owner really means, "The Truss rod is as loose as it can be, but the neck still has a back-bow" -- That would be a different fish to fry.

for the record i believe most two piece one way truss rods bottom out when loosened to the max if I'm not mistaken.  Either way... as you said if it's a matter of being able to somehow release a bolt vs replacing a truss rod i'd def lean towards the bolt!

[ElRay]

ALL: Thanks for the responses.

I received clarification, they meant "The truss rod is as loose as it will go and the neck still has a back bow", so this is a can of worms that I don't think I'll open at this time.

[Bizman62]

Good choice. Even if the truss rod were stuck some moderate banging and normal handling - even just strumming - should release the snag. Since that hasn't happened, it's either rusted or the woods of the neck have lived to create a backbow. My imagination tells that if the neck has been a bit too green during the building and the fretboard is a stiffer and/or harder than average piece of hardest hardwood, some longitudinal shrinking may be the culprit. Also, if the fretboard has been glued in place before banging the frets in, there's a possibility to cause a backbow if the wood doesn't give in and/or the slots are a tad too tight for the tangs.

Everything is doable, the big question being is it worth doing. The guitar still has a price tag included and on a wish list item "for nearly free" still can be a remarkable sum that isn't comparable to a learning experiment that can lead to failure.

Some time ago I got a classical guitar with a broken top and a loose bridge. The spruce veneers cost me a tenner, the workshop hours a bit more. Many things should have been done better but as the goal was something that can be played by a fireplace and finally burned I just hasted through the process and the result isn't structurally too sound.