you dont. you go buy a locking diff.
Or... You pull the cover and drain all fluid. Clean out ALL residual fluid with carb clean. Repeatedly. Pre heat with torch. Weld spider gears to side gears first. Start as deep as you can so you leave room for multiple passes. Make sure you have good penetration. Alternate sides often. Then inner gears to carrier, same rules apply. Do not quench. The longer it cools the better. Install cover, add fluid, go 'wheeling. Do not drive on the street ever again, because this is the redneck way to do it. I am not a welder, or even a mechanic. But it worked for me.
Mt jeep wrangler has a dana 35 differential in it
Not from the factory.
80w90
Rear differential locker button is depressed.
80w90
YesYes
It could be differential bearings.
Yes if it is the same length & after refitting the end of the jeep drive shaft to bolt up to the ford rear end
They can be a tenth off.
Ceck out "what type of automatic transmission fluid is needed for a 1993 Jeep Cherokee sport and in the front and rear differential" on wiki-answers
3 quarts per axle
It sounds like your rear differential may be on its way out. When gears come lose in your rear differential it tends to make grinding noise because things are not secure on the inside of the case. Teeth maybe missing or may have been grind down on the inside. In any case, I would start looking for a replacement rear differential for when your rear goes, take a look around craigslist or search around for a rebuild kit. The more research you put into this the less of a chance you have of getting screwed over by the mechanic who will be fixing your Jeep. Rears can be a pain in the rear end and that's how mechanics make their money. :-)