GL-3-5 all purpose lube will work for some transmissions, but GL-5 lubes (with a few exceptions) contain sulfur. Brass, being a soft metal, is dissolved and eaten away by sulfur.|
So what are you to do?
This is where some of your high end synthetic oils; Amsoil, Lucas, Royal Purple, and Red Line come into play. All of these companies offer gear lubes covering your transmissions needs without the damaging sulfur.
Why Red Line if all these oils cover my needs without the sulfur?
Within your transmission is a friction dichotomy. Your Jeeps transmission needs as much slickness as possible to prevent wear, but at the same time you need a certain amount of friction so that your transmission operates properly. A transmission using GL-5 is going to have a different slick/friction need than a GL-3/4 transmission. And many GL-5 transmissions use sulfur in the lube to keep internals clean and gunk free. This is where the MT90 fits our AX-5, AX-15, or any other brass synchro transmission needs... it has NO SULFUR.
So how might you be damaging your transmission?
Many lube shops and dealerships may be unaware of the damaging effects of an all purpose lube covering GL-3 through GL-5 (sulfur containing) lube. I found this out when my local Jeep dealership recommended a Mobil 1 synthetic lube. Per their recommendation, I put it in my transmission. Over the course of a couple weeks my transmission started acting up. No longer did it shift very well, and I started catching gears when shifting. The dealership didn't have any suggestions or solutions as to what happened and why I'm having problems out of the blue.
Finding no answers from the Jeep dealership "experts", I started doing research in other places. This was when I first learned GL-5 typically contains sulfur, and of the consequential brass issue. I mentioned it to the dealership and they were unaware of there being any compatibility problems.
My transmission was getting noticeably worse, and I wasn't getting any further in figuring out the answer, so I contacted Mobil Oil directly. I told them what transmission I had, and the course of events leading up to my transmissions health turning south. They immediately responded with a direct order to get this lube out of my transmission. They explained that it had a HIGH content of sulfur for GL-5 applications (although the product covers GL-3-5) and should never be used in a brass synchro transmissions.