Dan4governor

Hey guys, just got my AX-15 back from the rebuild shop and the guy told me that it was better to use 40w motor oil in the tranny instead of 90w gear oil. Have any of you done this or heard of someone who has done this? I just want what is best for my new tranny so it lasts as long as possible. What are the pros and cons of using motor oil v.s. gear oil?
Thanks,
Dan

BuckB91XJ

Never heard of that madness before.

TennesseeXJ

ummmmm.......you dont use motor oil or gear oil in a transmission...you use transmission fluid. Never go to that mechanic again...ever. Using gear oil in your tranny will just get you back into his shop

winston427

And you paid that guy to rebuild your transmission? There is reason one is called motor oil and the other is called gear oil.

96rhino

no freakin way, No freakin way! Make him pay for the mopar fluid out of pocket and fill it and drain it twice. Ask any rep. manual transmission repair shop. I'm not even sure I would accept the rebuild... WTF?

Metmknice

Some manual trans use GEAR OIL for their fluid. So do not be talking that madness. I dunno about the ax-15 tho, havent had one in years.

http://www.jeepforum.com/forum/showthread.php?t=512104

Thats a thread on ax-15 fluid that I jsut searched for quick. So the falsification of using motor oil is not as unbelieveable as you may think.

96rhino

some do, but not the ax-15, and not most automobiles. A long time ago......

96rhino

its the syncros you have to worry about. many times I've read posts of the amazing improvemnet in shift with royal purple or other non-recomended fluids. that extra smooth shifting lasted 5k, and almost every owner got pissed and switched back to factory, or had to change their royal purple syncronization mesh again, and after the next issue, it was back to factory!

5-90

The AX-15 likes 70W80 or so gear oil - GL-3 spec (that is important! The use of GL-4 or GL-5 will eventually dissolve the bronze synchroniser rings - GL-5 faster than GL-4.)

The "heavier" varieties of engine oil have been successfully used in various manuals as a substitute - often in high-mileage applications (where a good deal more lubrication is needed) or in very cold climates (where you don't want your transmission packed with something akin to butter in consistency.) In fact, many newer manual transmissions (particularly front-wheel-drive applications) specify something like 10W-30 or 5W-30, and I've even seen Dexron II/IIE/III specified for some manual transaxles as well!

Madness? Hardly.

Dan, I'd probably use the specified oil for break-in (the first 30-50Kmiles,) then you can swap to engine oil afterwards. If you've just had a full overhaul, you've got plenty of new parts that will have to lap in to each other (grinding down the last of the burrs on the gear teeth) and the operating heat and cooling action of the oil also help to temper the gears (which is important to gear life,) and they're designed to do that using proper gear oil. Once you've gotten everything run in, you can switch.

This is, in fact, an old trick I learned 'way back when I was overhauling Muncies and A833s for use in street/strip cars, for wringing out that last little bit of power. The lighter oil also cuts parasitic drag in the gearbox. Less power lost in the powertrain means more power to the wheels, and put on the ground where you want it!

Dan4governor

well...I don't know what to do. My transmission guy has earned a huge amount of respect around orange county as a manual transmission specialist and a jeep transmission specialist. I went to him cause I found out that people drive to CA from AZ and NV to go to him. I've talked to other mechanics in the area and some swear by this trick and some say to avoid it at all costs...let me know if you guys find anymore insight to this idea.
Thanks for your help.

BudgetXJ

Here's a thread on Naxja with some info about this.

http://naxja.org/forum/showthread.ph...30+ax15&page=6

Its about using 10w30 but its along the same lines. Some imports use 10w30 from the factory in their manual transmissions. Granted the XJ may be a heavier duty application but I'm considering trying it as its supposed to well.

Throttle Jockey

when in doubt, go with factory recomendations. they use speific oils to get expected results. how ever many miles you had before the rebuild will be roughly what you can expect using the factory recomended fluid.

Dan4governor

after lots of pain staking investigation and talking to who knows how many jeep and/or transmission specialist (which can't seem to agree on any fluid) I have decided to use 75w90 gl-3 spec gear oil, probably redline MT90. Any suggestions on what to put in my transfer case?

nick_n_ii

The AX-15 uses Auto Tranny fluid.

mark's91-XJ

the ax-15 uses 75-90 gear oil i know i have one just rebuilt.
your Transfer-case will use transmission fluid.

not sure if i would put motor oil in it,
i dont think it would hold up for very long.