I have 70's Martin D 35 that came in with over .020" relief in the neck... the fret board had already been thinned to about .155" at the nut in the center of the doubt adding to the weakness of the neck.. the guitar had a fairly recent re fret so rather than suggest a new board and re-fret I thought I could get the neck with the thin board to straighten out with re-enforcement. 

    I pulled the neck and did the carbon fiber rod / epoxy re-enforcing in the square tube truss rod, clamped the neck straight and let it set up for 24 hrs.  After re-setting the neck and string up,  relief was reduced but only to about .014" ... I was hoping for about .008" or less and so was the owner.       

   So... I removed the thinned down fret board, planning on replacing it with a new one.... and with
the board off and a straight edge on the face of the neck I had the same .014" relief in the center of the neck. Now in an attempt to find out what is bent,  the wood or the truss,  I heat up the tube and get it out of the neck and the tube itself has the same relief. I've read posts that say these tubes don't usually take a bend but this one sure has and to make matters worse I have epoxied in that curve forever. My first thought was to get a new square tube rod and start over but on a whim I flip the rod over and push it snugly into the neck reversing the curve from relief to back-bow the
neck is straight with just a little back-bow ... around .007" measured at the nut without even gluing in the truss rod...!!! 

   Well I think I have a good feeling about gluing this thing up with the flipped truss rod and a new fret
board but not sure…  I was just wondering how you guys would handle something like this and in particular.... how to glue the truss rod. I will be using hide glue of course and I'm wondering if I should glue in the rod first and then glue the fret board on after the rod has dried or can you glue both the board and rod at the same time...

   this is not my first time working on one of these necks but it is the first time I've had one of these truss rods out.

   Sorry for the long post and thank you so much for the
forum and the wonderful expertise that is so graciously shared.


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well I guess I'll up date... I glued the flipped over truss in the neck first and let it set over night... then glued on the new fretboard... put in a nut and strung it up with no frets. The neck pulled into .004" relief. not wanting to add compression with the frets I smashed the barbs and dressed down the tangs just a bit...then I glued and clamped the frets in the new board with hot hide glue... anyway all is good with the neck....guitar plays and sounds great.... the neck pulled into the same .004" relief with the frets in. and I thanked my lucky stars.
Good work, Fritz. Yes,I think you had a little luck, but it was luck mixed with a lot of careful thought on this one. The idea of flipping the rod around wouldn't have occurred to me, but it certainly will in the future.

Just so I'm clear, did you flip the rod end-to-end AND "over", or just over? Either way, it's opened-up my thinking regarding these old square-tube rods. I thank you for sharing your story.
Good ending, good job.
I would have fill the rod slot and re-slot it using a modern adjustable rod.
thanks Mike... lots of head scratching with this one for sure... I say the luck was that I didn't end up with a neck that was still back bowed even with string tension!!! ugh .. I think I came pretty close..!!! I kept the rod with the same orientation to the nut end and the 14th fret .. just turned it over... the relief I saw when the rod was out of the neck was pretty much centered on the length of the rod but I kept the nut end at the nut after the flip anyway. And thanks Pierre, I always consider installing an adjustable in these things, although I haven't yet, but the owner was not interested... and I do think these necks have a sound that is all their own with the non-adjustable rod... especially when they are filled solid. This guitar now has sustain and clarity that I seldom hear in any guitar. Now If I can just get the fret ends exactly in line with each other on the neck binding... I'm getting real close but seems there is always one or two that slip to one side or the other on me....just a bit...
thanks guys so much...
Fritz, you obviously did a great job on this, but I think you were being unduly pessimistic when you say that you had "epoxied in that curve forever".

I would bet long odds on that even with the CF epoxied in, you could get still rid of the unwanted relief by judicious tapping of the rod with a ball pein hammer on an anvil.

But hey, all's well that ends well !
Thanks for the kind words Murry and your probably right ... unfortunately in my humble little "repair only" shop I have nothing that big and flat and heavy.. I was also afraid the CF might brake or shatter in the tube if I started trying to make it bend back...I guess judicious is the magic word.. :)
anyway I know everybody loves pictures... I'm not sure if I should up load pics here... but a picture or two can be seen at this photobucket web site.
strike that... what I meant to say was "I'm not sure how to upload pics here"... I have since found the camera icon at the top of the reply page.

this is the rod out of the neck showing relief


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