What oil in a manual tranny

I have been getting conflicting stories. I have a converted to stick Cherokee which now has an AX15 in it. Which is the proper gear oil. I have heard to use the same as a differential, use engine oil and weirdest was to use Dextron III in it. Anyone give me the right answer??

general consensus seems to be: use redline mt90, if you can find it. it's a pia to find sometimes, so like some others(and per the new factory recommendation) i switched to 10w30 motor oil in mine, specifically mobil 1. i figured it doesn't take much and doesn't get changed but about once a year, so why pinch pennies? seemed like good insurance too. got almost 223K on mine now, 10w30's been in there for about 6 months now, shifts PERFECTLY. i'm happy with it.

I've been running Redline MT90 for several years in my AX15. It's NOT GL5 with the sulfur additives, and is synthetic. The transmission shifts much nicer in colder weather with the MT90 in it.

You need redline mtl or mt90 regular gear oil contains sulphur and will attack the brass syncros it happened to my tj. Got my redline at www.myoilshop.com

The AX-15 uses yellow metal (sintered bronze) for the synchroniser rings. The sulphur-based EP lubricants typically added to GL-4 and GL-5 gear oils are antagonistic to yellow metals - so choose carefully!

The AX-15 is spec'd for GL-3 gear oils (the axles want GL-5.) However, some synthetic GL-5 gear oils are formulated for use with yellow metals (no sulphur) - and they will say so on the label somewhere, using a statement to the effect of "Safe for Brass & Bronze" or "Safe for use with yellow metals." Check front and back.

Since the transmissions favoured for use with the performance crowd use bronze rings, that's why performance synthetics are usually safe for yellow metal. But check!

Any GL-5 spec gear oil can be used in the axles. The EP lubricants need not be sulphur-based, they merely need be present.

NB: Unlike the API engine oil specs (save "Energy Saving" SM,) the GL-x gear oil specifications are not typically reverse-compatible!

I have Valvoline synthetic 75w-90 in my 95. It's been in there for over a hundred thousand miles (it's now at 262k+) and I expect it will be in there when the poor old rustbucket finally dies of something other than transmission failure.

As 5-90 said, GL3 was originally specified, GL4 and GL5 not appropriate.

I am using Mobil 1 10w30 and couldn't be happier.

joe_peters said:

As 5-90 said, GL3 was originally specified, GL4 and GL5 not appropriate.

I am using Mobil 1 10w30 and couldn't be happier.

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Especially in colder climes, using engine oil in a gearbox is a useful little trick to know (or when you're trying to wring the last little bit of power out and get it to the wheels - I used to have strip drivers run 10W-30 in their old Muncies to reduce drag losses from pushing 80W-90 around...)

5-90 said:

Especially in colder climes, using engine oil in a gearbox is a useful little trick to know (or when you're trying to wring the last little bit of power out and get it to the wheels - I used to have strip drivers run 10W-30 in their old Muncies to reduce drag losses from pushing 80W-90 around...)

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My old Peugeot 404 and one of my old Mercedes specified 10w-30. Oddly enough the other Mercedes with the same box specified Dexron. I tried both and found no difference.

Thanks everyone. I have a case or two of Mobil 1 20/40 so guess I will give that a go. Unless someone sees a problem!!

Use 10w-30 motor oil. The weight chart for oil is misleading. a 10w-30 engine oil, simulates a GL3 gear lube which is like 75-90 weight or whatever it is. Engine oil weight for the oil and diff lube weight is not based off of the same scale. If you were to bring you're truck to the dealer and get the manual tranny fluid replaced they would use 10w-30. I used dino oil i'm sure synthetic is fine too, and would probably be especially good in a really cold climate.

I changed from what i believe was the factory fill (previous owner) to 10w-30 dino engine oil @ 130k miles. NO DIFFERENCE was observed tranny felt absolutely the same (which is perfect). I would just start substituting different weight engine oils. stick w/ 10w-30! it only takes a couple quarts or so thats like <$10!!

My newly rebuilt gear box was giving me serious shifting problems almost right away. I switched from gear oil to Redline MT-90 and it shifts like a dream now. Been using it for about 2 years. I ordered it directly from Redline, online.