stratmondo is right, take a look at the holes in the wheels and the washer with that bend finger going into one of the holes, that's the combination number of that one wheel.
remove the stack, keep them in order because some rotate Left and some Right, rotate the washer with the bent pin and put it into the hole closest to your old combination, then put the stack back together and put the locking ring over it to keep it on the post.
here is a photo of a similiar lock taken apart and a blog discussing it.
http://mikesoldsafe.blogspot.com/2009/08/locking-mechanism.htmlhope this helps
Squelchtone