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Old 04-22-2012, 06:39 PM   #1
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Flushing out old fluids

As spring is here and I'll be doing a lot more offroading I figured I'll replace the fluids in my 98 4l 5 speed. My question is what should I replace and how do I do it and with what? Besides oil and power steering fluid, Ive already done that. Thanks!

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Old 04-22-2012, 07:21 PM   #2
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For your AX-15 5-speed transmission, use either a synthetic 10W-30 motor oil or Redline MT-90 which is also a synthetic. Either are fine.

For the transfer case, while any good quality ATF is fine, ATF+4 would be a good choice which is a sythetic too. For the axles, you need a GL-5 gear lube, the viscosity of which is not real critical. For normal non-towing needs, a 75W-90 is fine. If you tow or do extreme levels of offroading, a heavier viscosity like an 80W-120 or 85W-140 is fine. In the axles, I prefer a non-synthetic.

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Old 04-22-2012, 07:32 PM   #3
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I use Mobil 1 75w-90 fully synthetic gear oil in my ax-15. Shifts butter smooth. I also have non-synthetic in my axles. Is there a reason why you run non-synthetic in your axles jerry?
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Old 04-22-2012, 07:48 PM   #4
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Sorry to tell you this Crkid but Mobil-1 75-90 fully synthetic gear lube is actually not good stuff for your AX-15.

Per the information at Mobil 1 Synthetic Gear Lubricant LS 75W-90 you will find that Mobil-1 75W-90 uses sulphur-based additives to achieve its GL-5 rating. Sulphur-based GL-5 additives are bad/harmful to the "yellow metal" (brass) synchronizers in your transmission. No worries, it will not cause immediate damage but I would change it to a different gear lube such as Redline MT-90 which is a GL-4 75W-90 or a synthetic 10W-30 motor oil. The sulphur-derived additives used to give it its GL-5 rating will cause long-term accelerated wear on the synchronizers but it doen't happen immediately.

Old Mopar user guides incorrectly said to use 75W-90 GL-5 but that was later quietly corrected to recommend a 75W-90 GL-4 gear lube which does not have the sulphur-based additives.

There are SOME 75W-90 GL-5 gear lubes like from Royal Purple and Amsoil that are safe for yellow metals but they have to specifically say that which those two brands do.

No worries on the recommended synthetic synthetic 10W-30 motor oil recommendation seeming to be the wrong viscosity. 10W-30 motor oil and 75W-90 gear lube are essentially the same viscosity, gear lubes and motor oils are measured on two different viscosity scales.

On why I prefer a non-sythetic in my axles, tests from companies like Currie showed in extreme uses that the ring & pinion gears run cooler when filled with a conventional gear lube. For most of us, it's a non-issue.
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Old 04-22-2012, 07:59 PM   #5
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How would say mobil 1 synthetic 10w-30 compare to the mt-90? My jeep is a DD if that matters.

I'll just drain out the 75w-90 in my tranny and put it in my moms rear diff of her suburban.
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Old 04-22-2012, 08:09 PM   #6
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Either of those, Redline MT-90 or a good quality synthetic 10W-30, would be fine. If I was holding both in my hands at a store, I'd go with the MT-90 but that stuff is really pretty much only mail order from places like Summit Racing
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Old 04-22-2012, 09:43 PM   #7
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Now I've done some reading and I'm deciding between Mobil 1 10w30 or Pennzoil Synchromesh for my AX-15. which one?
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Old 04-22-2012, 09:45 PM   #8
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Alright thanks for the info Jerry!
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Old 04-22-2012, 11:18 PM   #9
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Quote:
Originally Posted by crkid View Post
Now I've done some reading and I'm deciding between Mobil 1 10w30 or Pennzoil Synchromesh for my AX-15. which one?
Pennzoil Synchromesh? Where'd that come from? That's not the right stuff for the AX-15.

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