My brothers XJ looses fluid from the transfer case somehow. (There are no visible leaks and it leaves no puddles but you fill it up and a month later you check it it is empty), Anyway, since he doesn't check it..Is there anything going on it in when it is just getting driven in 2WD that requires fluid? I hate to keep crawling under there and dumping fluid in all the time just to have it disappear. He only uses 4X4 in winter so the transfer case isn't engaged all thru spring-fall.

yes, bits are still spinning, and it will likely be trashed.

Does the transfer case transfer power only to the front axle when 4WD is engaged? And the rest of the time it's just loafing, not doing anything?

Or does it transfer power to the rear axle all the time, and to the front axle when 4WD is engaged?

(HINT: # 2 is correct.)

The front driveshaft still spin the chain around even in 2wd. All that rubbing and friction is bound to do damage eventually.

What year XJ does your brother have?

any chance that you have checked the ATF level since this has started happening?

If there arent any visible leaks then some is draing The Transfer case, the fluid won't just disappear or evaporate.

It does evaporate. The internals of the TC whip the hot fluid (ATF) into a foam condition and the vapors escape out of the TC vent. This is the nature of ATF. It usually takes awhile for the ATF to evaporate however.


Edit: ^^ This is why some folks use motor oil in their TC. Some motor oils are conditioned to resist foaming. I tried motor oil in mine but didn't like it because it made more noise than using ATF. I have been using B&M Trick Shift ATF in mine and it seems to run a little quieter and haven't seen any fluid loss.

It's probably one of the shaft seals and it's only leaking when the vehicle is moving. That's why no puddle. Not very bad but mine does the same thing on the rear shaft. And like other people said, no you can't run it without oil.

Transmission fluid stays constant. Just the fluid in the transfer case disappears. I am leaning towards it only disappearing while in motion as someone mentioned which explains no visible leak or puddle. I shall fill it up and make sure the whole thing is clean and dry then drive it awhile and stop and instantly look under it.