Re: YJ Transmission
For future reference, spend about 10 min. and fill out your profile. It will save many of these questions.
As for switching to a lower gearset for the AX15. I honestly have not heard of anything. You will be venturing into unexplored territory, as far as I am concerned. You could try looking as some of the foreign vehicles to see if they had the AX15 transmission(Toyota, Nissan, Isuzu...I think one used the AX15, but can't recall which or what gear ratios were offered). This is about all the help I can give you here.
As far as a rebuild yourself, rebuild someone else, buy rebuild, junkyard buy w/ no rebuild question. The riskyest will be to buy a junkyard tranny and just hope is will last. But if you find a great deal, and don't have any question of the age/abuse that that tranny has went though then it may be a good deal(I just sold mine to someone for $50). If you have good mechanical skills and have rebuilt transmission before then you may want to save some $ and do it yourself. The next step would be to buy the rebuild kit and hire someone to do the rebuild for you(make sure that you are confident in their skills as well, & they give you a warrrenty). The most expensive, is to buy a rebuilt transmission. But you get it quicker, and most always have a warrenty. The decision will be yours.
One upgrade you might want to consider is to move to an external setup for you clutch slave cylinder as opposed to the troublesome internal setup that you currently have. For this you will need a junk bellhousing from a late YJ(don't recall when exactlythey swithed to the external setup, but '94 sticks in my mind, might want to go brouse the factory service manuals in your local Jeep dealership) or up to '99 TJ(before they swithched to the NV3500)or maybe some later manual XJ's, and all of the associated linkages. Make sure to go ahead and get new pressure plates and clutch stuff if you haven't recently. Doing this will give you much less clutch problems.
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<font color=green>llll '90 YJ</font color=green>
<font color=green>"There are no shortcuts to any place worth going."-Anon.</font color=green>