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t case is automatic transmission fluid I've heard some people run 10-30 in it as well but manufacturer says ATF also I've heard people running 10-30 in the transmission but I'm not sure what the manufacturer calls for
 

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found an article saying mopar superseded the original 75-90 gl5 which they have a special part number for with a new part number that is 10-30 motor oil hope that helps from what I researched it seems to be a pretty highly debated topic at least the t-case is simple
 

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I have a 95 with the AX-5. I use Sta-lube GL-4 gear oil. You do not want to run a GL-5 UNLESS it says it's safe for yellow metal. If you search around you'll see a couple different answers that seem to work:

GL-4 (getting harder to find off the shelf)
Pennzoil Synchromesh transmission fluid
10-30 engine oil
Redline MT-90
 

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Toyota has always used motor oil in their Toyota R154 which is the same as the AX15. Japanese build good stuff the idiots at Jeep ruined everyone's syncros with GL5.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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What bout the BA-105 speed. FSM calls for 75-90wt, everyone else says 10-40w non synthetic. any opinions based on experience?
 

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NP231 transfer case takes ATF.

AX-5 and AX-15 transmissions take 10W-30 full synthetic. Some use gear oil. If you do, it HAS to be GL-5 rated.

The transmission fluid is a debate of its own...
 

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:pop:
 

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What bout the BA-105 speed. FSM calls for 75-90wt, everyone else says 10-40w non synthetic. any opinions based on experience?
There was a post on this forum a few weeks ago stating the differences between 75-90 gear oil and 10W-40 motor oil. The post stated that there is essentially no difference in viscosity. The poster presented some convincing technical data.

What we need to look out for is a statement on the container saying the product inside is "yellow metal safe" if a person intends to use gear lube.

I have an AX15 that I bought to rebuild and I'll use motor oil in it when I'm done. I used GL4 when I changed the oil in my current BA10. It took a bit of searching to find the GL4.
From what I've heard, there is no downside to using synthetic motor oil in our transmissions except the additional cost. For the few extra bucks once a year or so, why not use synthetic? It won't hurt and it just might help.

Good luck, L.M.
 
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