Just did this today after struggling for an hour trying to remove the top bolt (fill bolt) on the rear diff. It was totally stuck and I was frustrated.

 

I took out the jack put the ratchet in the rear differential bolt, put the handle at about 4 o'clock and slowly cranked the jack up under the ratchet handle until the weight of the car unstuck the bolt. It worked like a charm and was very safe because with the length of the stock jack crank handle you can get completely out from underneath the car.

 

Try it next time you're changing your gear oil!

been there done that, twisted off the end of the breaker bar.

 

make sure they are not super tight, make them snug by hand and maybe up to 1/4 turn.

I suppose it's because a 1/2 in breaker bar fits the dif drain/fill plugs and the tranny plugs are so large, but people always way over tighten them. Check the manuals and you will find the torque spec is only around 18-20 ftlbs for the diffs and auto trannies and 33 ftlbs for a manual trans.