three screws on the outside then what, how do i remove the big nut on the fan ?

 

It's really easy, just take the 3 or 4 long screws that hold the case together out and you may have to tap it apart with a rubber hammer, make sure you mark it somehow first so you can put the halfs back together the same way they came apart, and as far as the nut on the end the only way I know of getting it off and back on is with a impact wrench, if it's rusty you may want to put some penetrating oil on it first.

 

Putting it back together is the hard part. (like everthing) There are some slots in the back of the casing, you will have to put some nails or paper clips in the holes to hold the brushes in the out position so that you can put the casing halfs together. I belive the procedure is explained in the Haynes manual (along with pictures)