Woody’s Workshop : Truss Rod Adjustment

Today we will be looking at the different types of truss rods and how proper adjustment is important to the setup of your instrument and it’s playability.

As the seasons change, the weather and humidty in many parts of the country can vary greatly. This sometimes can cause the neck of your bass or guitar to shift. Maybe you notice some buzzing in the upper or lower registers or the action is really high in the middle of the fret board. Knowing how to adjust your truss rod can counteract these changes and allow you to keep your instrument playing and sounding great throughout the year.

The truss rod aids in maintaining a straight neck. It does this by providing an opposing tension to the strings and is an aid to the general construction and strength of the neck. There are three types of truss rods commonly used today: the compression rod, the two piece bending rod, and the two way compression rod. All three work in the same manner. Turning the adjuster clockwise tightens and adds tension to the rod causing the neck to bend backward counter act the string tension; turning the adjuster counter clockwise loosens the adjuster and reduces tension to the rod allowing the neck to bow forward creating relieve in the fingerboard. The two way rod differs from single compression and the two piece bending rod because it can compress the neck into a forward bow through adjustment without the help of string tension. The compression rod and two way compression rod are the most efficient in my opinion and in most cases can achieve the desired results with the least amount of effort. The bending rod in most cases require a little additional help when adjusting by exerting pressure on the neck to bend it back while tightening the truss rod. The truss rod must be working properly in order to achieve the best possible setup. Now we will explore it’s effectiveness in aiding the neck/fingerboard to remain straight under string tension.

There are several tools you will need for the task:

1. a professional straight edge: 18″ long for guitar and 24″ long for bass,
2. screw drivers: small and medium Phillips screw drivers and a standard flat tip screw driver,
3. truss rod tool that came with your instrument.*

First we will determine if the neck is straight by placing the straight edge along the entire length of the fingerboard from the first fret to the last. We are looking for the points of contact that the straight edge has with the frets. Make sure you hold the straight edge perpendicular (at a right angle) to the fingerboard. If the edge is only touching the first and last frets and there is space between the ruler and the middle frets then you have a forward bow; however if the ruler is touching the frets in the middle of the neck and not the first or last frets then you have a reverse bow.

We will address the forward bow first:

1. In the case of a non Fender instruments, remove the truss rod cover if your instrument has one,
2. Check the fretboard with you straight edge and make note of the amount of relieve (bow) there is between the middle of the fingerboard/frets and the straight edge. If need be, take a measurement with a small ruler to confirm the amount.
3. With the appropriate tool turn carefully the truss rod adjuster counter clockwise 1/4 turn to determine how tight the rod is. If the adjuster nut is very tight I recommend that you remove the adjuster and apply some oil or bearing grease to the threads on the rod then snug the adjuster back up and recheck your measurement again before proceeding.
4. Now begin turning the adjuster clockwise 1/4 turn at a time checking with the straight edge at each 1/4 turn interval. You should see an improvement in the bow with each 1/4 turn until the board is relatively straight and you have consistent fret contact the length of the fretboard. If the adjuster becomes tight never use additional tools for leverage, at that point refer to a professional.

In the case of a reverse bow:

1. Check again the extent of the reverse bow and note how many frets are not touching the straight edge at the top and bottom of the fingerboard,
2. Begin turning the adjuster counter clockwise checking every 1/4 turn until you see the board respond and the upper and lower frets come into contact with the straight edge. The ideal situation is a small amount of relieve (bow) and the instrument will play cleanly.
3. In the event that the counter-clockwise loosening of the adjuster does not result in the reverse bow coming out consult a professional. You may have a warped neck which may require extensive repair work.