If I wanted to upgrade rearends what would be recommended and how much would it cost me? How can I know what i have now, Im pretty sure it doesnt say on the door
The factory rearend in your 92 Bronco is a Ford 8.8". You can try to beef it up, or better yet swap it with a Dana60 or GM 14bolt. A guy down here wants $1000 for a complete 14bolt ready to go. Anywhere from $500 & up. If you want rear discs, get one from the newer F250's, I believe they are still using the Sterling 10.25".
Check the metal I.D. tag bolted to the rear cover plate on the axle. It will tell you the gear ratio and if you have the factory L/S. Something like "3L55 8 8 "on the bottom row of numbers. The "3" may be covered up by the bolt holding the tag, so look for the "L" at least.
IF you do a search on Yahoo for "Ford 8.8", you'll find several companies that offer upgrades to strengthen the 8.8".