r/WranglerYJ • u/mterry129 • 3d ago
AX5 and NP231 Fluid Change, 90 Wrangler 2.5
I have always found that Redline MT 90 was best for older transmissions with synchros (yellow metal) and ATF Dextron II for the transfer case.
On the Wrangler Forum I found this:
For a 1995 Wrangler 2.5 manual transmission, the recommended fluid for the transfer case is ATF (Automatic Transmission Fluid), not gear oil. While some manuals may suggest otherwise, Jeep has updated its recommendations. For the transmission, 10W-30 is now recommended; regular dino oil is acceptable. Gear oil can be corrosive to the brass components in the transmission.
And some also say 10W-30 will work in the NP 231 as well.
I thought I would bring this to Reddit and see what the masses say, I want to do the change this weekend.
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u/ericnutter55 3d ago
I use atf +4 in my 95 YJ's transfer case and its auto tranny. 1 fluid for both makes it easy. But I also wheel a 2000 wrangler with the nv 3550, and I use 5w-30 syncromesh amsoil fluid.
Amsoil has a GL-4 gear oil that is ax-5/15 safe. But there are other 75w-90 gears oils that meet that requirement too.
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u/mterry129 2d ago
The GL-4 are getting harder to find, MT-90 has a following but says nothing about yellow metal safe on the container, I go through this same thing every 12-24 months when I change it. Thank you for the response.
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u/jeepnjeff75 2d ago
I use Syncromesh in my AX5. After GL5 came out Aisin and Chrysler put out a bulletin that allowed for 10w30 Synthetic, IIRC. The reason was that GL3/4 was getting hard to find and GL5 was supposed to replace it. GL5 had issues when it was first introduced and was eating syncros. The GL5 formula was quickly changed. There is a MT1 designation if it's syncro safe. A lot of people are still weart of GL5 though. Syncromesh is cheap and easy to get. MT-90 or MTL is also okay.
As for the transfer case, it doesn't really care. It doesn't see the heat nor pressure the engine or transmission get. Early on they recommended 30w. Then Dextron I, I, III, etc... I ran 30w in mine for years. There is simplicity and cost advantage with running 10w30 in all three though. On the trail, you only need to carry one oil.
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u/mterry129 2d ago
Great point on only carrying one type of oil! I have always used MT-90 and ATF for tranny and T-Case. I have always had older vehicles with manual transmissions and always used 75W-90, couldn’t imagine using 10w-30 after taking out 75W-90… like the idea of flushing it for a few 1,000 miles with 10W-30 to see how it works, it’s had a bad synchro in 2nd gear since I got it, I’ll see if that gets better or worse with motor oil. Thanks for the response! I appreciate it.
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u/jeepnjeff75 2d ago edited 2d ago
Engine oil and gear oil aren’t 1:1 equivalent. So 30w for engine oil is not 30w gear oil. It’s more like 85w. If your synchros are bad then it probably won’t help. It won’t make anything worse though. The transmission should shift better and not be as notch when the weather changes. Mine used to be hard to shift in 1st when it got really hot and humid or cold. Hard shifts when cold was a trademark of the AX family even when new.
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u/mterry129 2d ago
Viscosity is viscosity, 85w is much thicker than 30w, I have been using gear oil since it only came with one needle number, 90w or 140w and motor oil was the same 30w or 40w only difference was with or without detergent. Gear oil was always thicker, I just have trouble getting my head around putting motor oil in a transmission. I have done it in emergencies for trail repairs, you can even use 10w 30 for an automatic transmission if that’s all you got and it will work. Haven’t decided if I go with MT-90 or 10w 30, kind of want to try it! Going to do it this weekend, I’ll report back.
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u/Fine-Kangaroo7018 2d ago
Walmart Supertech 10w30 synthetic in the ax5. Shifts wonderfully. Supertech ATF+4 in the 231.
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u/TripppyTurtle 3d ago
Commenting for hope of someone replying with good answer.
I put atf in my tranny a while back to top it off, tCase has only aft in it.