A friend of mine has a Martin jumbo, I think J40, around 2010, with a fairly stff action. The action is stiff, partly due to too much relief, which is not possible to adjust with the truss rod. The nut seems to be tightened as far as possible. The nut seems to be well hidden under the tounge. Is it possible to screw the nut out in order to place a shim in front of the nut?
Does nobody know if it is possible to screw out the truss rod nut in a Martin J40 - 2010 (without removing the neck)? I am 200 miles away from the guitar, and I have no possibility to find this out myself (found nothing about it on the net).
If it's WAY up under there, it's a two-way rod, and the nut won't come off. If it's close to the soundhole, you can take the nut off and lubricate it to get better action. I con't recall the year of transition, but it's most likely this is a two-way.
Bob, from your comment that the nut is "well hidden" I think Frank is right about the 2-way rod. The nut doesn't come off.
Try backing the nut off enough that it moves freely, and clamp the neck to a stout board such that you induce a little back-bow. Then firmly snug the nut down again.
Hope that helps.
Thanks. I will send this to the owner, but I am afraid that I will be the one who will do this. If this is not enough, I will iron the neck flat. Btw, what is the critical temperature for the Martin bindings?