Ok, so I'm looking to change the Differential fluid, transmission and transfer case fluids on my 95 XJ with the Dana 30/Dana 35 axles and an AX15/NP231(? the part-time 4wd one) out of a 94 XJ.

Looking at the FSM for the 94, it indicates the AX15 should use 75w-90 gear oil. I read a post regarding a '96 and someone was very specific that you need to use GL-4 oil and NOT GL-5 due to a higher sulpher content that could damage the synchros. However, the FSM very clearly indicates that GL-5 gear oil should be used.
Can someone that has actually successfully changed their AX15 oil without problems confirm? Even better would be a recommendation for good gear oil. I'm kind of afraid to change the oil myself since I had a 2000 TJ and it wasn't long after I changed the oil (of course it could be the NV3550 which seems like it's kind of a crappy tranny... I had issues with the thing from the beginning.. as the regional mechanic manager for the entire northeast -assured- me that the neutral rattle was normal and not a problem...) that the tranny blew a bearing.

As far as the differentials go, the FSM indicates SAE90 for the rear gear oil or 75w-140 for extreme duty. It looks like SAE 90 oil is typically used in motorcycles or boats. Does anyone know what's up with this? The FSM definitely specifies 75w-90 as expected for the front diff, so it's definitely listing straight sae90.

In short, could I get some recommendations for the diffs, tranny and transfer case lubricants that people have had success using (particularly in the 94-95 model years)?
My jeep is running quite well at the moment, so I really don't want to f it up just because I want to do the proper maintenance.

 

For the trans I r eccomend a good manual trans fluid like Red line mtl the newer gl5 gear oils have additives in them that like to eat the syncros in older manual transmissions I am not sure if the ax15 is like that or not. For the differentials I run 85w140 in both of mine but 75w90 would be fine also.

 

For the trans, Redline MT-90 is absolutely the best (it's a touch thicker than their MTL.
I've tried various grades of motor oil and the MT-90 is noticeably smoother. I would not recommend running 10w30, my trans did not like it. 15w40 Rotella was better, the Pennzoil Synchro mesh stuff was probably as good but the Redline is the best, absolutely worth the price.
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For the diffs, run 75w90. I like AMSOIL or Chevron Delo gear oils but realistically any good 75w90 is fine.
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Transfer case I run ATF+4, but it will take Dex/Merc or the Valvoline synthetic transfer case fluid as well. ATF+4 is licensed by Chrysler and is supposed to be a very tight spec, meaning all ATF+4 is more or less identical. I run just whatever is cheapest and change it every 30k miles.
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I was leaning towards that, so it looks like MT-90 is the winner for the tranny fluid change. I wonder if that's what the PO used since the tranny is pretty damn smooth right now.

 

Pennzoil syncromesh is more for manual transmissions that use atf instead of gear oil it is slightly thicker than atf but thinner than the lightest gear oil, I wouldn't use it in a manual trans that calls for gear oil.

 

I have a 2WD so I can't answer your transfer case of front diff question but, for rear diff, I used Amsoil Severe Gear 75w140. Check out the chart to see how some other gear lubes tested...

 

I used MT 90 as well for the AX 15 transmission . I am sure you figured out the whole process by now, but I put together a little video detailing my personal how-to.

 

Yes sir. Running MT-90 and it's fantastic.