on the TJ the front axle acts in the same way the rear axle does, the spider gears and carrier / ring and pinion are always turning when the tires are turning, so the front shaft is always turning, what allows the shift on the fly 4wd and the reason you have to be rolling at a very slow speed to shift to 4L is the output shaft in the t-case for the front shaft is not engaged until 4H is selected, that slides the drive gear along the output shaft and engages power to the front shaft. (This is how I understand it after having all the components apart for various reasons, doesnt mean I have it totaly right lol). for the record, if the t-case housing isnt damaged, its an extremely simple thing to rebuild and as long as you are in the least organised when you dissasemble it you need no real experiance, in fact, get a slip yoke eliminator and 90% of the parts you need are included in that and its an upgrade you will want to do at some point anyway. Good luck and let us know what you find.