Here we have a Rickenbacker 12-string guitar with the typical Rick dual truss-rod system. The system generally works well, but has several design flaws, which have worked together to blow the neck of this guitar apart. The fingerboard has separated from the neck, and that the truss-rods are bent into the headstock. For those who are not well versed in the design and operation of these truss-rods, a quick explanation is in order: a Rick truss-rod is one long piece of flat steel, bent back over itself and inserted into the neck, with the bent end at the body and the twin ends at the headstock. Of the two ends at the headstock, the lower end is threaded and protrudes through a small aluminum block. The upper end is not threaded, and contacts the block. When the truss-rod nuts on the threaded ends, are tightened, they push the aluminum block against the non-threaded ends. This causes a back-bowing force, which counteracts the force of the strings, allowing for adjustment of neck relief.
This particular Rickenbacker’s faulty truss rod has created several problems: The first is that the aluminum block is not sufficiently long to support the threaded end without deflecting. This deflection causes the threaded ends to bend downward, making the truss rod ends dig into the headstock. This makes adjusting the rod difficult or impossible, as a wrench will no longer fit on the nuts. The second problem is that the non-threaded ends have climbed up the bent block, which acts like a ramp, and have exerted enough force to split the fingerboard from the neck. The third problem is that the threaded end of the rod is bent, and the threads are damaged.
What we had to do here is to repair the split fingerboard/neck joint, fix the bent and stripped truss-rods and make a longer, more supportive block so that this does not happen again.
The first order of business was to pry the aluminum block off the bent truss-rods so that the rods could be extracted from the neck. After the block was off, we were able to grab the rods with a set of pliers and slide them out.
The truss rods had drastically bent from the pressure exerted by the block. We needed to cut back the ends and re-thread them, and then make a new block, which would be long enough to support the tension of the truss rods. We milled the new truss block out of solid aluminum, ensuring that the truss rods ends would never bend and tear apart the neck again. In order to provide room for the new, longer block, we had to cut the rods back to fit; using a Dremel cut-off wheel, we cut the ends back enough to allow us to re-thread them.
We re-threaded the ends with a threading die to provide a proper fit for the truss rod nuts. There was enough thread to allow for the oversized block, and we ramped the non-threaded end slightly to help it push down, away from the fingerboard, minimizing the chance that it will split the neck again.
Next we dealt with the split fingerboard/neck joint. After cleaning the old glue from the joint, we glued it back together using clamps and a caul to avoid damage to the neck. After the glue dried we re-inserted the truss rods, and installed the new aluminum block.
The new block has three times the area of the old block, which will make it impossible for the ends of the rod to bend. This will also keep the nuts clear of the wood, allowing easy adjustability for many years.