What kind of gear oil?

[Gettin-Higher]

I'm getting ready to change the gear oil all the way around this weekend. Any suggestions on what kind/weight to use where? I'm thinking synthetic but have no idea what to use where. Also how much should I expect to use..

89 YJ 5speed stock axles.

[Gettin-Higher]

anyone.. bueler... bueler... :D

Actually I've decided on Mobil1 Synthetic all around.. (still trying to find out why the tcase uses ATF fluid though) Should I put 75/90 in the trans and diffs, of should they be different? Also how much should I expect to put in?

Finally, since I'm switching to a synthetic, what would be the ramifications of just pumping out the oil rather than removing the diff covers?

[Stubbs]

Why use synthetic in your diff's?? It's really expensive and it's one of the oils most frequently changed...

I must change mine 5-7 times a year. (depending on the high water mark inside the jeep :D )

Just use a good gear oil 75-90 or whatever. Save yer bucks on the synthetic stuff for the engine!!

[Paulwpetrea]

Well, as far as the transmission goes, I just installed a new one, in my Jeep (well last month), and I have in it, an will only use in it ... www.redlineoil.com

It is quite pricey, however to me, worth every penny.

As far as the differentials go, I use a good 75/90 weight lube in them.

In the transfer case, I put ATF in it. I realize I should probably go with something better, just haven't really pushed to do it, yet.

[Lauti]

The NP-200 series transfer cases - so the NP231J - have all (most) an aluminium case and are chain-driven. Somehow those cases get pretty hot when in use, so engineers decided to use the thin automatic transmission fluids, to better transfer the heat away from the internal moving parts to the aluminium outside case.
I would stick with ATF for the transfer-case!