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Ax-15 fluid


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Some observations on gearbox oil.


Bought my MJ with 202k on the clock,ran it for 3k before I started having issues with the transmission kicking out of 1st when shifting into it from a stop. Figured I'd try a fluid flush and see if there's any change, so I swapped it for Mobil 1 10w-30 full synthetic motor oil. This has been recommended many places online as modern GL-4 and GL-5 gear oils are not brass friendly. My notes from this:


As soon as I swapped in the Mobil 1 I noticed shifts were easier, felt "slick".


Didn't help or hurt the shifting issue at first.


Did notice on long highway trips 2 things. 1. The shifter handle got much warmer to the point of being too hot to comfortably grab at the shifter joint. 2. After an hour or so at highway speeds, downshifting from 5 to 4 was difficult. It would feel like it "hung" in 5th. Annoying, esp when the rest of the gears (except 1st ) were so slick.



After about 3000 miles the problems have gotten worse. 1st gear is almost unusable, and periodically it kicks out of 2nd when downshifting (never on the upshift). Figured my tranny needed a rebuild anyway so I swapped fluids again, this time to a GL-4/ GL-5 fluid 80w-90, conventional. Notes on this:


Drove straight from Atlanta to Baton Rouge (about 8.5 hours of highway time). Most notable was the lack of heat on the shifter handle followed by the ease of downshifting from 5-4. Major improvement there. The rest of the gears weren't quite as "slick" feeling but nothing felt notchy or stiff.


Once I got to BR, my around town driving was improved. 1st is still finicky but usable and I longer get kicked out of 2nd when downshifting. Tranny still needs a rebuild, but I'm convinced now that motor oil belongs in the motor and I'll risk sulphur eating my synchros over friction for sure damaging things.



Last note, my gas mileage on this trip (Atl-BR, Sept) averaged 19.4 mpg loaded over 2 tanks. My last trip with the Mobil 1 (BR-ATL, May) averaged 17.7 mpg with an empty truck.


Sent from my SM-G930T using Tapatalk

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Tranny needs a rebuild anyway. The GL-5 was much cheaper than anything else. It's staying for now, I know people that have run it for years without issues.


I have a junkyard tranny that's going in in the next few weeks while I rebuild this one. It'll probably get GL-5 for cost reasons too.

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100k on my ax15 with mobil 1 10w-30.

280k total on transmission.

Shifts smooth with no issues.


Around town it was smooth as butter, I could do everything with one finger. It was only on the extended trips at highways speeds that I noticed the heat and 5->4 shift was just a little notchy.
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