Since my Jeep was used and had 65000 miles on it when I purchased it, I wanted to replace all the fluids and do some other maintenance things that may have been over looked in years past. In short, I wanted to get to know my Jeep better and give it the best chance of a long happy life. First stop, change tranny oil in the AX-15 transmission.

Finding the type of fluid and capacity.
To be honest I have never changed the oil in a manual transmission but I have changed the oil in many automatic transmissions and am very handy with a wrench, so it should be no problem. I started by consulting the owners manual for the type of oil and capacity. The manual specified the use of Mopar blah blah blah oil or API GL5 80w90 oil. It did not however state the capacity and after looking at the tranny, I guessed it would take 2 or so quarts. So off to the parts store to pick up 2 quarts of Mobil 1 75w90 full synthetic.

Draining the oil and inspecting things.
I proceeded to remove the lower plug and drain out the current oil. Unfortunatly Jeep did not put much thought into the design and placement of items for routine maintenance and so the drain plug is located right over the edge of the skid plate. Luckily I have an old Tupperware funnel that worked great for redirecting the flow of oil away the skid plate and down into my pan. After removing the drain plug, I inspected the magnet and found that there to be a fair amount of metal on it. I also noticed that after the oil was drained and examined, there was a quite a bit of brass floating around in it. With this new information, I will assume that this will be the first time tranny oil has been changed. Another piece of info I gathered was that much more than 2 quarts of oil drained out of the tranny. Jumping online (where I should have looked much earlier, more on this later on), I found that the AX-15 requires 3.3 quarts of oil.

Replacing the oil
I did not happen to have a nice little gear oil pump so I had to make other methods work. I did have a pour hose that ataches to oil bottles but the threads are different than the ones on gear oil bottles. So I removed the clear hose, placed a zip tie around the end and tightened it enough so that it would click onto the bottle where the cap clicks. Then I just squeezed the the bottle and in went the oil. Not as efficient as a pump but it sufficed. After sqeezing in the 2 quarts and knowing that that was not enough, I nicely drove over to the parts store and picked up a third.

Did the Mobil 1 help?
Honestly it feels like there is less friction in the transmission. When I was putting around off-road, it felt ever so slightly easier to take off in 1st. But as a whole, things did not change much.

Further reading and new discoveries
This is where things get interesting. When I was searching around for the capacity of the AX-15, I found some interesting info about different oils and this transmission. First off, it seems as though Jeep misprinted the owners manual and the line API GL5 80w90 should read API GL3 80w90. The difference between these two standards (all that I care about anyhow) is the high sulfur content of the GL5 oils. Seems that GL5 oil will damage the brass synchros. The fix? Change the oil to something that is GL3 or GL4 rated. The easiest way I found was pick up some Red Line MT (Manual Transmission) oil. So I jumped on Jegs.com and ordered 4 quarts of Red Line MT-90 oil ($7.99 each + free shipping + $8.99 handling).

Re-changing the oil
After changing the oil once, I wanted to look for some kind of pump to aid in transfering the oil from oil pan to waste container and from container to tranny. I stopped by and saw the friendly people at Ace Hardware to check out their pump selection. What I found supprised me, as they had many different types of pumps for all kinds of applications. And the one that caught my eye was drill powered. And now $13 later, I have a drill powered pump that works great and aids in making huge messes while one figures out all the ins and outs of ones new pump. That said, once I got the hang of the pump it made transfering 90w easier than ever before and soon my tranny was filled with about 3.25 quarts of Red Line MT-90 oil. The Mobil 1 oil that had been in the tranny for a little over a week was placed in temp containers and set aside for the front and rear diffs.

Final thoughts
Did the Red Line oil make a big difference? No. However I do know that it is a superior oil to what was in the tranny to start with and I expect a slight bump in gas mileage, but mostly I am just happy in knowing that there is new oil in the tranny.