Late 70s Fender Jazz Bass Neck Straightening Challenge

According to The Guitar Dater Project, this Fender Jazz Bass "was made at the Fullerton Plant (Fender - CBS Era), USA in 1977 - 1978." That's the good news. The bad news is that it was submerged during the great flood of 2013, and damaged beyond repair (so thought the original owner). Rather than let this beauty go to waste, he gifted it to the current owner; pro bass player Albert Yap. Albert, in turn, wasted no time in sending the bass to a luthier friend in Jakarta.

That luthier did an awesome job of restoring this vintage Jazz Bass, I must say. As the original sunburst finish was a goner, he stripped the body and refinished it natural. The neck was also refretted with jumbo frets and refinished in a very impressive vintage tint. One critical point: the luthier did warn Albert that the truss rod was maxed out, and could snap if anyone ever tried to tighten it further.

Everything was roses until the day when the neck started to develop excessive upbow, resulting in overly high action that made the bass unplayable. Remembering that the truss rod was already maxed out, Albert brought it to me in the hope that I had an alternative solution.

Flexing the neck told me that the truss rod was still intact and doing its job. I inserted a 1/8" hex wrench into the bullet nut, and it was frozen solid -- I couldn't even loosen it! After a few days of heat/cold treatment and lots of lube, I managed to loosen and remove the nut completely. There was lots of gunk to be removed from the inside threads of the nut and threaded portion of the truss rod, that I can tell you.

After taking measurements, I realized that it wasn't the truss rod that was maxed out; but rather the nut itself. The threaded end of the truss rod had reached the end of the threaded channel of the bullet nut, and that's why the nut could not be tightened any further. So now, I had to find a way to create more space in the threaded channel of the nut. 

Based on this understanding, I fashioned a couple of truss rod washers that would be slid onto the truss rod before threading on the nut. If all went well, I'd then be able to tighten the truss rod even further. But first, I had to clamp the neck and use heat treatment to gradually force it into a backbow, exposing more of the threaded portion of the truss rod; thereby creating space for the washers. This approach was effective, thankfully; and I was finally able to tighten the truss rod until the fretboard was dead flat.

This being achieved, it was time to do a fret dress. The frets were leveled and recrowned in the usual way, and the bass restrung and tuned to pitch. The sun was shining, and the birds were singing. It was a happy day when Albert came to pick up his beloved bass. Understandably so, for he'd not seen his baby for close to two months.

Then, about two weeks later, he called me to say that the bass had become unplayable once more. History had repeated itself! I was sorely disappointed, to say the least; and told myself that I had better settle this matter once and for all. This time round I repeated what I'd done earlier, albeit going a little more aggressively on the heat treatment. After a month or so, I managed to get the neck to behave itself under tension. Final adjustments were made by Albert himself (he normally does his own setup); who declared the bass playable.

I'm keeping my fingers crossed that the neck stays this way for many years to come, and gives its owner countless hours of bass-playing pleasure.