The string action height on a banjo is measured at the twelfth fret. The strings should be above the fret about 1/8 of an inch. Remove the resonator to see which type of adjustment is on the banjo. These bars or rods have several functions. First, they hold the neck to the rim or pot. Second, they keep the rim from going oval because of the string pressure from the tailpiece. Third, they are used to adjust the height of the string from the fretboard. There is not a standard method for all banjos. Each manufacturer has different ways to adjust the string action on their banjos. In the last 100 years, there have been many adjustment inventions. Some adjusters are lock nuts on a threaded rod, turnbuckles, clamps and pins, shims, even the old ‘screw-in-the-woodenbar’ types.
Older banjos will have a square wooden bar going from the neck to the tailpiece end inside the pot under the head. It is usually fastened with a large screw that also holds the tailpiece. This is a fixed bar that requires an experienced person to either shim the neck or change the screwhole to a slot to move the string action. Not recommended for beginners. Put the resonator back on and keep on playing. Newer banjos have a single or double steel rod with adjustment nuts.
This adjusting function is a tricky one. By adjusting the lock nuts on the rods, you can raise or lower the string action height. This is also an experienced person job, but I will explain it to you. The adjustment method used on Gibson banjos is nicely described in a 1930’s catalog. Gibson and their clones use two threaded rods with nuts and washers.
The rod closest to the head is called the spacer rod. This rod uses an internal thread and washer to keep the neck held tight to the pot. Usually a small hole in the middle of the rod is used to tighten this rod to the neck. Use a small nail or allen key to turn the rod tight. The neck and rim must be tight together to transmit the sound properly.
The other end of the spacer rod has a nut and washer. This nut must be tight enough to prevent the pot from going oval shaped, and the nut and washer not rattle. If too tight, the sound will be dampened. Just about 1/8 turn past finger tight is enough. You can experiment with the sound after you have adjusted the second rod correctly.
The rod furthest from the banjo head is called the adjuster rod. This rod also has an internal thread and washer to hold the neck tight to the pot. You may have to loosen a nut at the far end in order to turn the rod to tighten the neck to the pot.
The Gibson Method
‘To draw the strings closer to the fretboard, insert a nail or punch in hole in center of rod to prevent turning. Loosen inside nut and tighten outside nut’.
“To draw strings away from fretboard, reverse the nut adjustment’. (Loosen outside nut and tighten inside nut).
Please do these adjustments very cautiously until you have success in raising or lowering the string action height. Measure the height of the strings above the 12th fret. The average height is 1/8 inch for low action to 3/16 inch for high action. My preference for best playability is 1/8 inch.