If you have been following this series you know that at this point we have progressed to a completed but bare wood bass body and neck. The routes are cut, it has holes for jacks. It is fretted and has a set of truss rods.
The neck is the most important part of most stringed instruments. Year after year, season after season the neck is expected to maintain its shape and hold to an impossibly narrow specification despite temperature and humidity changes. It is also expected to cope with different string sets and even different playing styles without so much as a wimper. Too much deflection back or forward can make the instrument difficult if not impossible to play. The way your bass neck can handle all of these potential changes is the adjustable truss rod. The earliest mentions of adjustable truss rods in patents date back to around the turn of the twentieth century. According to Wikipedia the first truss rod patent belonged to Gibson and dates from 1921. Of course the article goes on to say things about Rickenbacker truss rods that are not exactly right so I have to wonder. Anyway, the basic idea of a truss rod is to add a counter force to the pull of the strings. This is usually done by lengthening or shortening a slightly curved steel rod that is anchored inside the neck.
Here, shamelessly stolen from Wikipedia, is the side view of a typical truss rod assembly. Notice the front to back curve of the rod channel.
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I am amazed by how many players are afraid to do their own truss adjustments. This is just plain silly. The fact is, it is one of the things you can do yourself that you probably pay to have done. There is no shortage of horror stories about neck adjustments gone. Well, I say pay no attention to any of them. Follow along here and you will be able to do all of your own neck work when ever you want and save yourself some money at the same time. That way you will be able to buy me a beer at the next confluence.
In a relaxed state (no tension applied) , the rod lies in the channel and exerts no force on the neck. The wood alone carries the load. When the nut is tightened, the rod is effectively shortened and wants to straighten out. It pushes against the center of the curve and levers the neck backwards away from the pull of the strings. The opposite happens when the nut is loosened. That's it. It is really that simple. It ain't rocket science. This is how nearly all truss rods work including those made after August of 1984. If your bass was made prior to that time, the rods are of an entirely different type.
The old style rods are made of about 4 feet of steel flat-wire that is folded nearly in half with one end being about an inch longer than the other. A thin piece of electrical tape lines the inner faces of either side to minimize rattles and vibration. The long end is threaded to 10-32 and uses a 1/4” hex standoff as an adjuster nut. The assembly works like this. The long end of the rod passes through a thick aluminum bearing plate and the short end stops up against the bottom of the plate. As the nut is tightened the halves of the rod are forced apart. The bow in the middle becomes an increasingly stronger spring. In a relaxed state, these rods are flat and more or less loose in the neck. The amount of spring tension applied to by the rods determines how much back bow is induced on the neck. This one is a little more complicated but still does not require an advanced degree to understand.
The upper rod is of the new type and lower is the old type.
Tools
The tool you use to adjust your neck is just as important as the method. The official Rickenbacker tool is the best choice. Mine is always within reach. They cost less than $20 and are available from any Rickenbacker dealer. You might even find the same or very similar tool in you local hardware store. It is an Xcelite L8 ¼ inch nut driver that looks like this.
New Style Rods.
The current Rickenbacker truss rods are made of 5/32” round steel rod stock that are cut just a little longer than the fingerboard. One end is the fixed anchor which is a star washer on a nut and acorn nut locked together. The other end is the adjustable anchor which is a 1/4” hex standoff with 8-32 threading that sits over a thin steel thrust plate. The rod itself is wrapped in 1 inch wide masking tape to prevent rattles inside the neck. On basses made after 1985 the fixed anchor is at the body end just north of the neck pickup. You can see the domes of the acorn nuts sitting just inside the end of the fingerboard under the guard.
The E side rod has been removed in this picture. The G side rod shows the typical depth of the acorn.
