Adjusting a neck equipped with a Double Action Truss

by Brian Calvert

First of all you will need to check your neck for the proper amount of forward bow, you can do this by using an 18" steel straight edge and placing it lengthwise down the center of your fret board while the guitar is tuned to proper pitch and in players position! Players position is the guitar setting properly in your lap the way you would play it, If you try this procedure with the guitar laying flat on it's back the neck will not be in it's natural position, gravity plus probably the tip of the head stock will cause it to bow in a different position throwing off the measurements you are trying to gauge.

Make sure that one end of the straight edge is touching the center of the first fret and the other is touching the center of the last fret.

Now take a feeler gauge (you can purchase one of these at most automotive stores) and check the clearance at the 7th fret. If there is less than .005" clearance you will need to turn the truss rod nut counter clockwise. Do this in 1/10 of a turn increments and recheck the clearance. If when you checked the 7th fret you found that there is more than .015" of clearance then you will need to turn the truss rod nut in a clockwise direction. Remember to move it only in 1/10 increments as it will move allot with each turn, and recheck the clearance often.

Below you will see pictures of the common types and where the truss rod nut is located
On many guitars you will find the truss rod nut located underneath a cover on the head stock of your neck
View of a standard Allen wrench style adjustment truss rod
For some guitars you will find the truss rod adjustment on the other end of the neck which may mean you will have to remove the strings and take the neck off to make an adjustment.
If you do not have a straight edge or set of feeler gauges to help you check for the adjustment you can always have a friend hold down one of the outside strings at the 1st and last fret while you try to slide a playing card under the string at the 7th fret. The card itself should barely slide under the string without lifting it, so adjust your neck to the proper setting from the results you observe.
Pictured above are the two most common style of truss rod adjustment tools an Allen Wrench on the left and a barrel style socket wrench on the right, If your adjusting the neck on say an older style Strat neck you may need to use a flat bladed screwdriver instead.
 
On to Step 1: Head Stock Area
On to Step 2: Truss Rod and Neck Bow adjustment (You are here)
On to Step 3: Nut Height check and adjustment
On to Step 4: String Height and Bridge adjustment
On to Step 5: Adjusting the intonation of a guitar
On to Step 6: Adjusting Pickup Height