Originally Posted by
Simon Barden
Two things to consider before shimming.
1. Is the neck almost straight with just a slight concave bow in it? If not, adjust the truss rod (clockwise = straighter, anti-clockwise = more concave bow). Hold a string down at the 1st and 17th frets and see what the string gap is like in the middle.
2. The nut is very high at the moment. It will need to have the fret slots cut deeper. This will lower the overall action considerably. You won't want to do this until the bass is all put together, so just hold or tie the strings down (a guitar capo is useful for this) at the first fret, then you'll get a better idea of the action with the nut lowered.
I'd do both of these exercises before deciding on any shimming requirements.