Acoustic Guitar Truss Rods: Correcting an Adjustment Gone Wrong
Q: I have a second-hand 2017 Martin D-16E. When I got it, the action was too high. I thought I could correct it myself, but through a series of missteps I ended up wrecking the truss rod. So I will now try to replace it. Is there anything quirky about the truss-rod replacement for this model—does it involve neck removal or some other can of worms? —John Lussier
A: I’ll admit, this is not a question I field every day! I frequently encourage my clients to get familiar with truss rod adjustments, as they are a straightforward and necessary adjustment that can make a big difference between an easy-to-play guitar and a tendonitis creator. However, even the most straightforward adjustments can have their pitfalls. I’m sorry to hear you’ve discovered that the hard way!
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The easiest and most common error is using the wrong size wrench to adjust the truss rod—adjusters vary between 1/8-inch and 5mm (or even 6mm on a few older imported guitars I’ve handled), in both metric and imperial (USA fractional) sizes. There are lots of close fits in that range, but I can only stress: use the correct tool. A wrench that is slightly undersize can cause the nut to strip out, rendering the rod nearly impossible to adjust. If you have any doubt about the correct size wrench, get online and do some research, or call the manufacturer.
A trip to the hardware store to get the exact right-size wrench is quicker and cheaper than a truss rod repair. There are specialized tools and techniques that have been developed by creative luthiers to remove or extract stripped nuts—my first suggestion would be to bring your guitar to an experienced repairperson, to determine whether the rod is indeed wrecked, or whether it can be restored to function by replacing the nut. If the nut is slightly stripped but still operable, StewMac’s tapered Truss Rod Rescue wrenches can be lifesavers.
The other common issue with rods is breakage from overadjustment. This occurs less frequently, as the neck usually ends up far beyond the desired position before the rod gives up. However, if the neck wood itself has warped forward, then the rod sometimes ends up tightened almost to its limit just to straighten the neck without string tension. In those cases, sometimes the rods are not able to overcome the combined pressure of the neck wood and the strings, and can break as a result. In my experience, the most common breaking point is just at the rod’s shoulder, where the plain steel transitions into the threaded portion that engages the nut.
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If you’ve determined that the rod is indeed broken, then the course is clear—the fretboard needs to come off. I use flexible heaters to warm up the glue joint until I can insert a palette knife, and then patiently open up the joint. This can also be done with a household iron. I must stress that there are more than a few risks here—any plastic or composite parts near the heat (fretboard dots, bindings, nut, etc.) can be at risk of melting or discoloration, as can the finish around the fretboard extension. After removal, I quickly clamp the fretboard to a rigid flat surface to help keep it flat enough for reinstallation afterward. At this point, the rod can be extracted and replaced, the gluing surfaces cleaned up (vinegar works well to soften most common wood glues), and the fretboard reglued. Care must be taken to keep the neck straight during regluing, especially with the added weight of the clamps. Once it’s back in place, it will need finish touchup along the edges of the joint, and most likely around the fretboard tongue, and usually some leveling and recrowning on the frets.
This is not beginner-level work: given the value and quality of the instrument in question, I would absolutely recommend having it done by a professional with repair experience. It’s easy to make a bad situation worse in cases like this. But, if you really wish to charge ahead with fixing it on your own, I’d encourage you to watch videos, read everything you can, and even try removing the fretboard from a cheap yard-sale guitar first, to get a feel for the process and the pitfalls. Jumping into new territory always feels safer when there isn’t as much at risk.
