Restoring a non-functional truss rod to working order can be one of the more complicated jobs that a luthier specializing in repair may have to undertake. In many cases, replacing a broken truss rod will require removal of the entire fingerboard, which is a costly and invasive procedure. On the more simple, single action style of truss rods, the removable adjustment nut is made out of a softer material, such as brass. This ensures that the truss rod nut will strip out before the rod itself sustains any damage. Replacing a stripped truss rod nut is a fairly straight forward procedure, in most cases. Some instruments have a double action truss rod, which allows the user to actively add relief, rather than relying on string tension to add relief. This style of rod does not have a removable nut, and requires the entire fingerboard to be removed if the rod needs to be repaired or replaced.

Most American Fender guitars made from the early 1980’s on have a biflex truss rod, which is very similar in design to the traditional single-rod style of truss rod. The biflex truss rod has a walnut plug that will prevent the adjustment nut from coming out of the access hole. This allows the user to add relief by loosening the truss rod nut until it pushes against the walnut plug. If the truss rod nut should ever need to be removed and replaced, this walnut plug will need to be carefully extracted first.

This particular Fender Stratocaster has a lot of neck relief, and the truss rod nut is at the end of its adjustment range. Most likely, someone cranked on this truss rod aggressively, compressing the wood around the nut, and causing the rod to bottom out in the nut, while still leaving a great deal of relief in the neck. I’ll need to remove the truss rod nut and add washers, to extend the range of this truss rod, but first, I need to carefully extract the walnut plug.

I do this by applying heat to the truss rod nut. I insert the tip of my soldering iron into the hole in the plug, and slowly increase the temperature, in order to heat the plug and loosen the glue. Once the plug is sufficiently heated, I’ll insert a 1/8″ allen wrench into the hole, and I’ll loosen the nut until it encounters resistance. Then I’ll give it another quarter turn or so, so it’s pressing into the walnut plug. I’ll continue to heat the plug, both with the soldering iron, as well as with a heat gun, until I see the finish start to separate around the plug, at which point I know the plug is working its way loose.

Next, I’ll continue loosening and backing the truss rod nut out of the adjustment channel, pushing the plug out with it. I’m able to get the plug a little more than halfway out using this method, until the truss rod nut slips off of the rod completely. Then, I thread a screw extractor into the walnut plug, which I’ll use to slowly pull the plug loose with a pair of vice grips. The screw extractor cracked the walnut plug in the process, but this isn’t a big deal, as I’ll be fabricating and installing a replacement plug when I’m done here.

Once the plug is out, I scrape the remaining glue residue from the truss rod access channel while its still warm. Then, I take a look at the truss rod nut. When adjusting your truss rod, its important to make sure that you’re using the right size wrench. In the case of this MIA Fender, we want a 1/8″ allen wrench. MIM Fenders take a 3/16″ allen, while Squiers commonly take a 4mm allen wrench, but have used a 5mm allen wrench in the past (Korean made Squier bullets, for example). Chinese made Fenders and Squiers also take a 3/16″ allen. MIJs sometimes take a 4mm allen, but not always.

It’s also important to make sure that the allen wrench you use is in good condition, and is not worn or rounded over. Otherwise, it can slip, and round over the recess in the truss rod nut head. And most importantly, never use a ball end allen wrench to adjust an American Fender truss rod. The allen recess in MIA truss rod nuts are very shallow, and a ball end allen wrench will not get enough bite. Continuing to use a ball end truss rod wrench on an MIA rod will quickly round over the recess, requiring the nut to be replaced My 1/8″ allen wrench for adjusting American Fender truss rods came from Stewart McDonald, and it originally had a ball end on it. I ground the ball off so that the wrench will completely bottom out in the adjustment hole, and I routinely grind the length of the wrench down when it starts to become worn from use.

The truss rod nut on this instrument isn’t completely stripped out, but it’s starting to get there. I’m going to replace it for good measure, since the part itself is pretty cheap. Next, I’m going to add a few washers to the truss rod, giving myself a greater range of adjustment so I can straighten the neck out. My method for doing this, is I’ll lightly super glue the washers to the end of the truss rod nut, and then insert the nut into the adjustment hole and tighten it back down, working the washers down the length of the rod. The super glue has a light enough hold that the washers will break loose once the washers hit wood. In my opinion, this is the safest method to get the washers where they need to go; if you try dropping the washers into place with a dental pick, or a pair of hemostats, there’s a risk that they’ll slide down horizontally next to the rod, making them very difficult to extract.
I ended up installing four washers in this manner, two at a time. Now, its time to straighten this neck out. First, I use a steel leveling beam with two small wooden spacers, and a clamp, to force the neck into back-bow. Then, I’ll screw the truss rod nut on until I encounter resistance, at which point I’ll slowly tighten it, a quarter of a turn at a time, over the course of about a day and a half. My goal is to get it so that the neck stays slightly back-bowed once the clamp is removed. I end up adding a fifth washer during this process, for good measure.

Once the neck holds a bit of back-bow without the clamp, I’ll reinstall the tuners and string it up to tension with the customers chosen string gauge (in this case, D’addario .010 – .046) and leave it overnight. When I check on the instrument the next day, I see about .011″ of relief at the 7th fret, which is an improvement over the .048″ that it had to begin with. I tighten the rod a quarter turn, and the neck straightens to my target relief measurement of .004″ with adjustment range to spare. Now its time to disassemble everything again, and install a replacement walnut plug.

Fender supplies these plugs pre cut and drilled, but they were out of stock at the time of this repair, so I fabricated a replacement myself. I cut a short section of 3/8″ walnut dowel, and carefully clamped it vertically in my drill press vice. I then carefully drilled the 1/4″ adjustment hole down the middle of the dowel. It’s crucial that your drill press table is adjusted perfectly level and square in order to ensure the exit hole will be square in the middle of the length of dowel.
Once I’ve got the hole drilled, I cut a few small grooves into the plug, to help hold the glue. I then insert the plug into the access channel without any glue, and trace the shape of the oval access hole into the plug with a pencil. I then pull the plug out, and belt sand just up to this line. Finally, I wipe a little Titebond original wood glue onto the plug, and slowly slide it into the access hole. I then add a small clamp to hold down the thin end of the plug, to ensure it stays down until the glue is set.

Once the glue is set, I cut the plug level, using first a Japanese chisel, and then a razor blade, with scotch tape on the ends, to prevent them from cutting into the finish. I scrape with the razor until the plug is only protruding a few thousandths of an inch, and then lightly flex the razor blade, and slowly scrape it flush. Then, I mask off the fingerboard and overspray the nut and headstock with Mohawk Perfect Blend Satin Lacquer. This lacquer will perfectly match the satin finish on the face of the headstock. The spray tip on this can of lacquer sprays very lightly, with minimal overspray, and the Perfect Blend lacquer is formulated to flow out very thin and evenly. In most cases, it’ll match the sheen of the existing lacquer without requiring wet sanding.

Once the lacquer has had sufficient time to dry, I’ll reinstall the tuners and string trees, and then string up the guitar and proceed with the setup process. The new plug looks good;  it’s hard to tell it’s not original.