Last week when I was doing my brakes i noticed that their is an ajustment for the brake pedal behind the master cylinder.
you need to remove the master cylinder. my question is what is the correct way to make the adjustment on this shaft? I remember in my old VW days that if you adjust it to much your brakes will drag. Is their a special tool to do the job?

 

The rod is adjustable but like you said it's possible to make the brakes drag if the rod is made too long. In a way it's like adjusting a mechanical clutch linkage, you want a little freeplay in the adjusment or you'll burn up the trowout bearing. Likewise the brakes will fry if they are partially depressed all the time.

I'm sure that they have a jig or fixture that is used on the assembly line to set the correct lenght of the rod. It probably attaches to the master cylinder mounting bolts.

If you use your hand to slowly press the brake pedal down you might feel some slack in the adjustment but unless the factory setting has been disturbed I would just leave well enough alone.

Good luck.