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Old 10-02-2010, 07:20 PM   #1
TjTheo's Avatar
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Transmission Fluid

Ive researched alot on this forum and others and i couldnt get a straight answer.
What type of transmission oil should i use for the 5 speed manual transmission out of a 98 jeep tj?
Pretty sure it's the ax-15

Ive heard people mention 75w-90
and ive heard syncromesh.

If you dont get stuck, you're not trying hard enough.

98 tj 4.0 5 speed aka "rosie"
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Old 10-02-2010, 08:10 PM   #2
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Use the stock Mopar oil. I ran Royal Purple for about 10k miles, and my syncros haven't been the same since. I'm running nothing but Mopar oil now in the tranny.

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Old 10-02-2010, 08:58 PM   #3
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What Ray said, 10/30 motor oil or, if you don't mind spending more money, Redline MTL or MT 90 is real good. Yes, you have the ax15. Mopar discontinued the ax15 lube, so the dealer now recommends Mopar motor oil.
. . . . picking the lines with my twenty-nines . . . .

'99 sport 4.0 5 speed, top-of-the-line floormats
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Old 10-03-2010, 09:18 AM   #4
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Anything else?
If you dont get stuck, you're not trying hard enough.

98 tj 4.0 5 speed aka "rosie"
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Old 10-03-2010, 12:07 PM   #5
Knows a couple things...

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75W-90 GL-3 or GL-4 is the "official" spec though the manufacturer, Aisin, now also recommends synthetic 10W-30 engine oil. Don't worry about the wide variance in those two viscosities, 75W-90 gear lube and 10W-30 engine oil are essentially the same viscosities, gear lube and engine oil viscosities are measured differently.

A very good full synthetic GL-4 75W-90 is Redline MT-90 which has long been a favorite gear lube for the '97-'99 Aisin AX-5 and AX-15 transmissions.

Do not use Synchromesh.
When you have a choice, buy American.

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