The Gibson Adjustable Truss Rod System
Since 1926, all Gibson guitars (except classical guitars) have had the adjustable truss rod systems When the instrument is tuned to pitch there is a bending load on the neck. The truss rod is designed to compensate for this load and helps insure the straightness of the neck.
Should neck or fingerboard warpage appear (or different gauges of strings are used), the truss rod can be adjusted by removing the truss rod cover located on the peghead and adjusting the hexagon-shaped truss rod nut. This adjustment should be performed by qualified repair personnel only - improper adjustment can result in damage!
Newer Gibson banjos (after 5/1988) employ a two-way truss rod. Turning the nut clockwise will correct an underbow. Counterclockwise adjustment will correct an overbow. Again, this adjust should be performed by qualified repair personnel only - improper adjustment can result in damage!