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caposto 10-29-2012 01:53 PM

75w-90 GL-5 in the tranny case study...

I'd like to thank Chrysler/Mopar for ruining my transmission syncros. I'm a newbie to this site but have owned my '91 YJ 4.0L Aisin AX15 since it was new. I've changed the transmission fluid a few times now and have about 80K miles on it using 75w-90 GL-5 Redline gear oil in the tranny PER THE SPEC in the owner's manual and Haynes manual.

After reading some of the posts here that its the wrong spec oil for the tranny, and apparently Chrysler has confirmed that, I immediately changed my fluid yesterday. Its been hard to get it into 1st or 2nd from time to time especially when hot and R sometimes grinds getting in gear. After draining the fluid, I ran 2 quarts of old (but still sealed) Redline MTL through it then filled it up with Redline MT-90 (Its about 3.5 quarts fyi.)

I did find a chunk of syncro in the drained oil so there you have it. I'll be needing a re-build soon. Really unfortunate given I'm only following the specs and guidelines.

How is this not a recall or class action??

RednekYJ 10-29-2012 05:38 PM

I just dumped 5w30 conventional in mine. Not going to run it for long but it shifts alright

caposto 10-29-2012 05:51 PM

I just took it for a ride (and a smog-It PASSED Wooohooo!!) and it does seem to be shifting better with the MT-90 in there. If it doesn't deteriorate further, I should be ok for awhile.

Any suggestions on fluid or additives that might 'repair', condition, or help the syncros hang on now that I've screwed them up?

kik 10-29-2012 05:54 PM

I use full syn 75W90 in my AX15. It shifts great and no problems.

caposto 10-29-2012 09:27 PM


Originally Posted by kik (Post 2939228)
I use full syn 75W90 in my AX15. It shifts great and no problems.

If it GL5 gear oil as stated in the OM and SM, it will deteriorate your syncros OVER TIME. You won't notice anything immediately and it will shift nice until it doesn't.

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