Diff oil question(s)

[Jason4x4]

I'm going to try and change the gear oil in my differentials ('06 TJ) and possibly my transfer case as they may be contaminated. I took a look at my owner's manual, but I still have a couple questions, so I'm coming to the pros for help .

First of all, the manual tells me what type of oil to use in the diffs (80w90) and it says to fill until oil starts to come out of the fill hole. Ok. But how do I get the old oil out? Do I have to take the cover off of the diff, or is there another (better) way that I dont know of?

Secondly, it says to use 80w90, I'm considering using Redline synthetic oil. I see Redline offers a few 75w90 oils. They make an MTL, Heavy Shockproof gear oil, Synthetic Gear Oil, an a Superlight Shockproof Gear Oil. Which one should I use?? I have the D30/35 front (whatever is stock) and the D44 rear, if it makes a difference.

And how many quarts should I buy to be safe?

If I come up with more questions I'll post them later. Thanks in advance.

 

[Jason4x4]

Also, what would you recommend running in the transfer case? I see the manual calls for ATF+4 auto transmission fluid, but I don't see a lot of offerings for that. Can someone point me in the right direction?

 

[currupt4130]

Some of the newer difs have a drain plug at the bottom of the pumpkin on the backside. If yours doesn't have this, you have to pull the cover, re-seal the surface, put the cover back on and fill it up. As far as the difference in running 75w90 and 80w90 I don't know. If you have a limited slip in the rear (some came factory) you need to ad friction modifier to it to make sure you don't wear out the clutch packs.

In the t-case I've always run good old ATF Dexron-Mercon III. Do what your manual tells you or call the dealership to find out for sure. I don't keep up on the specs for new rigs, but I don't think they've changed the 231 enough to warrant a change to a new ATF. Any decent quality ATF should be fine, but that's just my .02.

 

[Utah_jeepster]

Now before you ask...most will tell you that they don't run a gasket on the diff covers, Just get a tube of RTV black and some brake parts cleaner.
pull the bolts and gently pry the old cover off and the oil will drain. clean off the old sealant and degrease the diff housing face. a 1/16 thick coating inside and outside of the bolt holes and bolt up the cover. I think the bolts are torqued to 20 foot pounds.
It takes about 2 quarts per axle to fill them up you will need to glue some hose to a cap to fill the axles or get a larger bottle of the stuff and a pump. You can never drain all of the bottle into the diff without having some sort of 20 inches of lift....ok a joke there but there isnt enough room under the jeep to dain the bottle into the diff while its sitting on the ground.

For general use 80/90 is the best. there is no need to get the higher end stuff you never going to generate the heat or torque needed for the other stuff and it makes changing it a lot cheaper. With a trac loc you will need to add friction additive. (Most stock D44's).

P.S. your front is a Dana 30....Dana 35's only came as a rear diff.

 

[Jason4x4]

Now before you ask...most will tell you that they don't run a gasket on the diff covers, Just get a tube of RTV black and some brake parts cleaner.
pull the bolts and gently pry the old cover off and the oil will drain. clean off the old sealant and degrease the diff housing face. a 1/16 thick coating inside and outside of the bolt holes and bolt up the cover. I think the bolts are torqued to 20 foot pounds.

You read my mind.

Now, I have what is probably a stupid question, but here goes - if I end up taking the cover off of the diffs to change the fluid, is there something holding the gears in? I don't have to worry about them 'falling out' or coming out of alignment or anything do I? Better safe than sorry, I guess...
:?|

 

[currupt4130]

Nope, no worries about them falling out, that is unless they're demolished in which case they'll come out in little pieces

 

[redrooster]

You could use a pump to drain the diffs, but really it's better to pull the cover.
As far as filling them, put 80W90 back in there like the book says. It may also say to use GL4. I have no idea what that means, but look at the back of the bottle of 80W90 and make sure it says GL4. Some only say GL3. I really don't think it makes a lot of difference thought.
Since you are filling both of them, buy your oil by the gallon and get the cheap hand pump that goes with it. It's got a hose, so you don't have to worry about squeezing the bottle in there upside down where you don't have room. Much easier and worth the 3 or 4 bucks for the pump. It will also be handy for filling the transfer case.

 

[jfrabat]

It will also be handy for filling the transfer case.

Not to mention the transmission when you decide to change that oil as well!