Transfer case is leaking and can't find manual for what I should use to fill it back up. What is leaking looks pretty dark and black rolling off skid plate, I would think it's just 90 weight gear oil or similar? But something makes me think it ATF 4? What is all over the skid plate and on floor sure doesn't loon like ATF fluid. Then again I bought used 6 years ago and have never touched the transfer case.

 

If you are asking what goes into the transfer case it's ATF+4. You should fix the leak first though

 

I haven't been under it to give it a good look, but the black oil like drip is coming off the back of of the skid plate. Never has had a leak there before, maybe I will take it in have have the leak fixed, hopefully nothing too hard. I can't do much right now, had an ankle replacement. Hard to even get down to look at leak, takes a long time to get over an ankle replacement.

Thanks, something made me think that wasn't 90 weight oil that a person was suppose to use, even though the drip doesn't look/smell at all like ATF fluid.

 

Previous owner could have put gear oil in it

 

Finely healed up enough I got under truck and the transfer case is full of nice red transmission fluid, some ran out as soon I got plug off. Darn plug must have been 1 3/16 inch, my 1 1/8 was too small and 1 1/4 too big. Anyway old crescent wrench got it off. While at it I took off skid plate (it was caked with oil and dirt) and cleaned it up as well as other areas under truck to find leak. Now I will keep watch. I have always had minor leak where transfer case connects to transmission, but never enough to worry about, kind of like the rear main leak. So small not worth fixing.