To recap, if is the neck is bowed in the middle, the truss rod will need to be tightened. If the neck has a hump in the middle, the truss rod will need to be loosened. It's pretty hard to hurt anything by loosing the rod. Old style truss rods are just metal rods that are threaded on top. There was no way to force the neck back by loosening it. Many newer instruments use rods that work in both directions. The only problem you can get into with these is trying to loosen it too much and stripping the threads on the nut. With these rods the nut is not meant to come off.

Adjusting the rod by tightening the nut is where the possibility of serious problems can occur. BE WARNED! The worst case scenario here is that you tighten the rod too much and break it. This is a really bad thing. It can probably be fixed, but not easily and will cost big bucks. So, ready to learn how?

A little basic info about the truss rod. It runs the length of the fingerboard inside a channel cut into the neck. There is usually a plate covering the end screwed onto the peghead and resting against the nut. Usually two small screws hold it in place.

To adjust the truss first remove the truss rod cover by taking out screws holding it on. You should see a nut inside a groove sticking out from under the nut. The standard size for these nuts is ¼ inch. I described the tool I use to adjust the rod earlier. This is a ¼ inch nut driver ground down on the outside of the business end so it would fit in the groove. I recently figured out that screwdrivers that have multiple bits are also designed to work as a ¼ inch nut driver and usually won't need to be ground down.

First we should get a feel for adjusting the rod itself. All adjustments to truss rods should be done by turning the nut as little as possible. Let's starting by loosening the nut. Turn the nut counter-clockwise until it just starts to move. You should never try to turn the nut more that 1/8 of a turn. Check the neck to see if it looks different. Loosening the rod should caused the neck to bow more. If the neck hasn't changed, loosen the nut a bit more until you can see a change.

Now let's tighten the nut back to where it was before. Turn the nut clockwise until it starts to move. You should be able to turn the wrench pretty much the same amount as when you loosened the nut. Check the neck again to see if it has changed. It should be back to the same position as before you started.