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Spike3
03-12-2014, 12:52 PM
This weekend is going to have super nice, sunny weather so what better way then to spend it outside having a Jeep improvement day. I've already got a new oxygen sensor that I'll install, but while I'm under there, I figured I'd change the oil in the differentials, transfer case and transmission (AX15 manual). The Haynes manual I have doesn't specify oils so I've turned to the numerous Jeep forums for help.

This is what I've found so far:
Differential: ~1.2 litres of 75w90 or 80w90 gear oil in the front, and ~1.7 litres of the same in the back (filled to the bottom of the fill hole, volumes are approximate).
Transfer Case: ~2 litres of ATF+4 (also approximated, I'll fill to the fill hole).
The transmission seems to be the controversial one. Some places say use 75w90 or 80w90 gear oil and others have said 10w30 engine oil. I've read to stay away from GL-5 gear oil because it will corrode the brass synchros and to get GL-4 rated. The motor oil weights seem pretty light so I'm not sure about that one either.
I found some 80w90 for $27 for a 5L jug, compared to 75w90 synthetic for $65 per 5L jug so I've bought the 80w90 for the differentials, but noticed that it is GL-4 and GL-5 rated, so maybe it doesn't corrode the synchros? It says on the front it's for manual transmissions and differentials among other things. Maybe I can use this? I don't have a link to it but it's Canadian Tire brand MotoMaster oil.
What do you use for your rig? What would you do if you were me?

As always, thanks a ton for your inputs! This forum has been a huge help!
-Spike

Edit:
This post (http://www.jeepforum.com/forum/f11/what-kind-gear-oil-do-i-use-my-ax-15-transmission-1326386/) seems very helpful in figuring out what to use. Also, according to Wikipedia, gear oils that are GL-4 and GL-5 compatible still have the yellow metal eroding additives, and that 75w90 gear oil has the same viscosity as 10w40 motor oil since they're based off of different standards. This makes everything much easier because I couldn't find any GL-4 only gear oils at Canadian Tire but will likely be able to find synchromesh-friendly motor oils there. The question still remains tho, what oil would you all recommend?

abebehrmann
03-12-2014, 06:22 PM
My 1999 owner's manual says only use SAE 75w-90, API-GL3 grade gear lubricant. I have the aw4 so I haven't read up on the AX15 but I don't think I would trust engine oil in the manual transmission.

XJMikey
03-12-2014, 08:57 PM
I was always told to use GL-3/4, or 10w-30 synthetic, or MT-90.

When I had a '93 YJ 2.5L/AX-5 (trail used, only), I ran 75w90 synthetic gear oil in it. I never had a problem when spending all day subjecting it to burning hot summer trail abuse.

Spike3
03-12-2014, 09:44 PM
I was always told to use GL-3/4, or 10w-30 synthetic, or MT-90.

When I had a '93 YJ 2.5L/AX-5 (trail used, only), I ran 75w90 synthetic gear oil in it. I never had a problem when spending all day subjecting it to burning hot summer trail abuse.

I'm going to a speciality auto parts shop tomorrow to pick some up. I'll try to get Redline MT-90 because that's what most of the people have recommended, but we'll see what they have and what's not ridiculously expensive.

Spike3
03-17-2014, 10:44 AM
I had to scramble around to find an oil transfer pump so I only got around to changing the transmission and transfer case oil. I haven't noticed much of a difference in either. Probably due to the fact that they have 567,000km on them and synchros are just warn.
For the transfer case, when it's cold and I have it in 4 full time and make a sharp turn, it hops as if it's in 4 part time. Is this normal? I thought it's supposed to activate the central diff. I have an np242.

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4.3LXJ
03-17-2014, 10:55 AM
In part time, the axles are locked together and will hop in a sharp turn if the traction is good in a sharp turn. In full time you can do it though

Spike3
03-17-2014, 10:57 AM
In part time, the axles are locked together and will hop in a sharp turn if the traction is good in a sharp turn. In full time you can do it though

Is it normal for it to hop in full time when cold tho?

4.3LXJ
03-17-2014, 11:06 AM
How cold? You Canucks can get some winter up there

Spike3
03-17-2014, 11:07 AM
It was happening a few days ago when it was 5C outside, so somewhere above 32F

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Spike3
03-17-2014, 11:08 AM
Also when it's really cold, I usually idle in neutral for a few minutes, but would it be better to idle in gear but put the transfer case in neutral so they're all moving around and warming up?

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4.3LXJ
03-17-2014, 11:10 AM
You sure you have the 242 tcase instead of the 249? It shouldn't be hopping in full time if it is a 242. The 249 has a fluid coupling in it and the 242 the spider gear diff in it.

Spike3
03-17-2014, 11:13 AM
I'm pretty sure. I'll look underneath later today. I'll see Jenssen in a week so I'll get him to test it out.
Thankfully all the snow melted so I can drive 2wd all the time now.

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