Try a remodel ceiling fan box

I'll assume you know how to safly handle electric. You can leave old box in place and mount new box on joist. Big box sell's covers for this type install. A secound way is mount fan on a j hook and swag wire between old box and fan. Again,ask for nessary supplies at big box.

OK, thanks, but you lost me. The area in the attic where the junction box is located is inaccessible (to do any work) to anyone except a really really small person. All work will have to be done from the underside of the ceiling. I originally bought this http://www.homedepot.com/p/RETRO-BRACE-with-4-in-Round-Ceiling-Rated-Pan-1-1-2-in-Deep-with-1-2-in-KO-s-936/203743171 for the job but the old box/hole is right against the joist and the ends of the brace need to sit on the drywall.

My hopes are not to have to make another hole in the ceiling. I think I can enlarge the current hole a little and the fan base will cover it.

Googled J hook but didn't see anything that looked like it would apply.

Yes, I can safely work with electricity. I wired our kitchen during it's remodel. I will also be running a new cable for the fan/light combo so both can be operated from a wall switch instead of climbing on the bed to pull chains.

For the moment forget about existing box and mount a new one dead center of stud by running screws through rear of box,through drywall into stud. Now run electric from old to new,mount fan on new box, cover both boxes with deep metal cover plus large plastic disk that is made for this exact purpose. What's so hard about that?

OK, but wouldn't that leave a considerable gap between the base of the fan and the ceiling? Can you provide a link to these items? "cover both boxes with deep metal cover plus large plastic disk that is made for this exact purpose"

Thank you.

Thank you. That's what I finally decided to do.