Drnaline,
I have a 98 with AWD and have been researching this conversion for a while.
I mentioned before that you can use a 4406 T-case out of an Expedition or F-150, but after getting my hands on one to try out, I found that it was just a little to much of a squeeze to get it to fit. So I abandoned that idea.
What your looking for is a t-case small enough that has the standard Ford 6-bolt circular pattern to bolt to the 4R70W transmission along with a 31 spline input socket.
If you want to go the simple, but expensive route, Advanced Adapters now makes an Atlas II t-case that will bolt right up. Unfortunately its about $2500 and you will need to cut slots in your floor for the shifters.
Call me crazy, but I prefer electric shift and Control-Trac. So upon further digging, I found that Advanced Adapters just so happens to make a transmission-to-tranfer case adapter that replaces the existing adapter with 6-bolts, with one thats a 5-bolt pattern which allows you to bolt a 1354 (91-94 Explorer) or 4405 Control Trac (95-01 Explorer) t-case to a AOD or an AODE (4R70W) the latter, happens to be the transmission AWD V8 Explorers have. This adapter is about $500 and comes with the new adapter with a 5-bolt pattern, and a new 25 spline output shaft for your transmission.
You can pick up a 1354 t-case with electric shift for around $300-$500 at a salvage yard. Along with the adapter kit ($500) , the labor to get the new output shaft installed in your transmission ($400), and a GEM module to control the t-case ($60), this whole process will run you back around $1500.
Darren
Littleton, CO
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98 Explorer Limited V8
-Front 4 inch Superlift(Ranger)+1 inch Torsion Twist
-Rear 5.5 inch Superlift SOA
-2 inch PA body lift
-33x12.50 Goodyear Wrangler MT-Rs