seperating the t-90 from the dana 18

could anyone help me with some directions on seperating these two without shafts and other stuff falling down, this is my first dance with these two so i dont know anything other than i have em out on the floor and i have removed the rectangular cover on the bottom of the 18 that has some gears in it. everything is fine with the two's performance but they leak oil pretty bad so im going to put new gaskets and seals in.
any detailed info on this would be great just remember im no mechanic and new with this
thanks for your time and knowledge
brad

 

The FSM has some good detail; also the Novak site has a good set of instructions on the D18. There is a very detailed discussion regarding this topic linked from the tech section on this site that deals with rebuilding the D18 and T90. It has most of the information you will need. I used all three of these at some point during my rebuild, and found each to be helpful at some point.

 

What the others said.
But basically I think you want to take the nut off that's holding the drive gear on inside the tranfer case. This is done through the round cover on the back (suggest an impact wrench). I think in some cases you could pull them apart without doing this step but I think it's better to go ahead and pull that gear off anyway.
I'm not sure on the T90 but like you mentioned the shaft could shift toward the back as you separate the two and then the gears and such could fall off causing you some work and head scratching. Go ahead and pull the top cover off the trans and tie that thing with some wire so it doesn't move back on you.
No need to worry about gears or anything falling out of the D18 xfer case.
Look up the instructions on Novak and other sites and print them out - you're going to need them anyway.
Just by the way you asked the question it sounds like you have some idea of what you're doing.
Good luck and keep us updated.
And, update your info so eveyone knows where you are.