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Well decided to switch to synthetic gear lube today.
Got me a couple quarts of Mobil 1 synthetic.
Changed the front one. no problem.
Got to the rear and opened the drain plug. All of a sudden...Whooosh..!!
Thing was pressurized in there. Found out that the breather plug was plugged solid from rust. Located upper right hand of the diff looking behind the vehicle.
Took it out (17mm) and dipped it in PB blaster for 30min. Got it freed up and bolted it back up.
Good thing I found this out early or I would be replacing axle seals and/or a pinion seal back there if the pressure decided to push them out
The easy way to access the differential vent is to lower the spare tire. You can then get right up next to the vent. (It is on the rear passenger side corner of the diff). Mine at 100K was completely coated in dirty grease and clogged.