...so a few days ago a strange humming sound and vibration started coming from underneath my Libby when I decelerate. First thing that came to my mind was a Universal Joint. Under the jeep I go later to find them to be perfectly fine. Time to take it to the shop. Its fresh out of warranty so I wasnt taking it to the stealership. I took it to a local shop thats owned by a Jeep guru. Next day I get a phone call...your differential is bad..HUH?? A chrysler 8.25 bad at only 81,000 miles!? I was in complete dismay. I had just replaced the fluid with Amsoil last year and it looked fine when i had the cover off. He called a salvage yard to get a price on a used rear end...$1500!? Sounds a bit ridiculous to me. Im checking into getting it rebuilt instead.
Anyone here have problems with theirs? I thought the 8.25" was a reliable rear end...am i mistaken?

I guess I'm glad I've stuck to the Schedule 'B' maintenance schedule even though I didn't really understand why it required a rear diff lub change at every 12,500 when Schedule 'A' never required one.

Funny thing is no one can ever fall into schedule "A".

I've got this buzzing, vibrating kind of sensation when I decelerate too. Been wondering what on earth it could be.

Funny thing is no one can ever fall into schedule "A".

Highlighted is what went wrong,sorry to say.Spent a few hours with some oil tech guy's the other day and there is a reason why synthetic gear oil is being used(to satisfy CARB) and why more frequent gear oil changes are mandated by the manufactures now even though synthetic gear oil is being used in newer diffs.Basically they needed to lighten heavy components by using less dense materials and the diffs are one of those areas that have been lightened,with the synthetic gear oil you must change every 15,000miles or trouble can happen from high heat that synthetic gear oil can not conduct.Synthetic gear oil is not better then dyno gear oil,it is actually worse at pulling heat away from the gears and bearings in diffs(works great in engines though).Thank CARB and change the gear oil often with synthetic or things tend to self destruct when ever they want.

I don't buy the "poor heat transfer" argument. I can't possibly fathom how the heat capacity of the synthetic versus dino base oils being significantly different...this quantity should be identical for all intents and purposes. If the heat transfer was that bad, no one would ever put synthetic oil in an engine.

One of the reasons synthetics are often touted is for their improved lubricity or slipperiness. Now if that is true, they should lessen heat build-up due to less friction. Another reason is for the flatter viscosity vs. temperature curve.

Now, there could be something to the argument of dino lube being better than synthetic lube due to the ability to carry heat, but it's going to take something more convincing than "it is because these lube guys said it was."