Thanks for posting the info here on CF and thats interesting that theyd say that after they told me to get the 75W-90 Specifically. Im not doubting RP quality in their products or anything but you figure that they'd have the right info the first time around considering how big of a company they've gotton to be.

 

Well, that's why I wish I knew who you were talking to. I have been talking to David for a few years now and he helped me out tremendously when a company was trying to screw me out of replacing some turbos. Here is some more in depth info he gave me;
Josh,

If you had a NV3550 manual transmission – I would highly recommend the RP Synchromax fluid. This is a fully synthetic fluid having the viscosity of an atf the oil film strength of a gear oil. It is a recommended replacement for any manual transmission that specs an atf or the GM Synchromesh (or equivalent) fluid.

Since you have the AX15, this transmission used to specify a GL5 80W90 or 75W90 up to year 1995/6 I believe.
In 1997, Chrysler / Jeep changed the recommendation from a GL5 to a GL3 to avoid the issues of lower quality EP gear oil additives causing poor shifting as the phosphorus component potentially plates out on the bronze synchronizers of the transmission. An API GL-5 gear oil contains a full EP (extreme pressure) additive package typically of a sulfur / phosphorus composition. An API GL-4 also contains EP additives but in conventional mineral fluids – usually only contains 50% of a GL5 to reduce any negative effects of the additives to soft metals if the oils are run past their useful life interval or at too high a temperature. An API GL3 contains no EP additives – hence the difference. See the attached API GL listings.

An gear oil SAE 75W90 fluid in viscosity is virtually the same in fluid thickness as a crankshaft SAE 10W40. See the attached comparative viscosity grade chart.

So for you application, in an AX-15 that is not damaged, the correct fluid is an SAE 10W40 Motor Oil such as the RP SAE 10W40 part # 01140.

If – however, the synchro’s have been damaged, or you live in a very cold ambient conditions you might benefit from using the RP 10W30 or RP 5W30 Motor Oils.

Cheers,

David

 

I can post the charts if anyone is interested.

 

 

Thanks alot for the post, that helped alot, and at the time when I was talking to the guy I hadnt thought about asking for his name, I will next time though. And Im not sure if the rest of the trans. is shot but Reverse dosent like to go into gear 50% of the time, So Should I go with 10W-40 or 30? If I got the motor oil Itd be $10 cheaper then the Redline because I only Need 3 Quarts for the transmission and They sell it here at my Advanced Auto.

 

You almost got that right. Its just the GL-5 that's not friendly to yellow metals. Most imports use brass syncros and specify GL-4. I know my miata and 240sx do. I personally run Amsoil 75w-90 GL-4 in my AX-15. Its cured transmission issues in my Unimog and in my other vehicles and has been the only thing to hold up well with my 400hp 240sx. Not to mention I can now get into reverse without having to go to 1st first.

The only vehicle I've used that syncro-mesh 10w-30 in is my Civic. But I've heard that's b/c its light duty; I don't know. If you do a vehicle search on Amsoil's website, it shows all fluids that are applicable.

 

ah I see

I wasnt 100% sure, I know that one of the GL's was bad for them

 

If it was me, I'd try 10W40 and then switch to 10W30 if the shifting was still crappy.
Since you are trying to save money, might as well go straight for the 10W30.

 

Only reason im trying to save money currently Is because tomorrow im going to be spending alot of it at the junk yard on an axle and some other parts. Id get some redline but Id have to pay for shipping. It'd just be more convenient to run to Advanced and grab three quarts.

 

I've always like RP more than Redline anyway.

 

Just an update to anyone who was wondering if the royal purple worked or not, I found now that ive changed out the nasty old fluid and filled with royal purple that my gear changes are smoother, reverse no longer needs any "encouragement" to engage and just slots right into gear as it should, I also used to have a noise from the clutch when I pushed in the pedal, that is also now gone. This stuff was worth every penny, seriously reccomend it to anyone that has an AX-15.

 

Which fluid did you end up deciding on?

 

I just posted Royal purple. Read my last post.

 

I think he saw that, he probably meant what "type" 75w-90, max atf, cripes you name it.. RP makes a lot of different oils..

 

Sorry for the confusion, I bought the 10W-40.