i decided to put new pads on the rear brake drum yesterday. it still had the stock pads that came in it brand new. the wingnut that you adjust was tightened just about as far as it would go. but the pad still looked new. it had 1 little groove worked into it. idk if its supposed to look brand new after 10 years or not, but they dont work unless the wingnut is tightened up a pretty good ways, and thats with the new pads too. im just wondering if anyone else has had this problem.

 

I would look at the Brake Cam and see if there is any were on the lobes on it. Another thing to look at is the brake arm that attaches to the cam on the outside could be out of adjustment if it has ever been taken apart. That could explain why you have to tighten the wingnut up so far.
You seem to be very mechanically inclined the only other thing I would suggest is maybe a factory service manual for your fourtrax as it is an invaluable tool when it comes down to it.

 

id get one but i dont have the 60 bucks. if i had the money id have one now.