I have an issue with my rear differential. The first symptom was something locking up when it is cold when backing up.
If I held some power on, it would reluctantly still back up. No issues moving ahead.
It felt like a bearing binding up and I immediately thought of a wheel bearing but when I jacked it up both rear wheels turned easily and smoothly ahead and both had a lot of drag turning backwards.
I proceeded to change all the gearbox oils (both diffs and transfer case). Oil in transfer case and front diff looked good with no cuttings, however the rear diff oil was quite black and the plug had collected quite a lot of fine cuttings but no chunks. There is no oil leakage or play in the input shaft and it works completely normally as soon as it moves around a bit.
Drive ahead about 400 ft and it will not do it anymore but I know something is not right so I'm hoping someone on here can give some advice.
My thought right now is that one of the crown gear bearings has lost its roller divider cage and the bearing is binding up but I don't understand why there are no chunks in the oil and the diff doesn't howl. Any ideas?

 

Does your diff have a locker?

 

No locker, open diff.

 

Could it be something other than the diff? Brakes? Transmission? Maybe jack up all tires off the ground to examine, engine running in gear.

 

I've wondered that too. I'm going to jack both rear wheels off the ground and remove the driveshaft. That will eliminate anything forward of the diff at least.
Weather warming up doesn't help in diagnosing as the binding seems to go away as soon as it warms up slightly.

 

JohnZo alluded to brakes....have you checked the e-brake? It could be binding up on reverse. There is an adjustment on it or the drum may need to come off and inspect. I had a similar thing when backing up and was able to mess with the adjustment screw. Easy to check and rule out.