Selectrac workings - 90 XJ

I have a 90 Xj with selectrac tcase and stock 3:55 gears (auto tranny)

I am swapping in a disc brake 8.8 with 4.10s and LSD in back and I have a D30 4.10 gear set to go in up front.

here's my dilemma - I am quite sure my D35 is about to blow up - very growly at certain load conditions - could just be a worn bearing that sounds worse than it is but ya never know. The 8.8 is ready to bolt in (proper perches, discs all set up, pinion flange will bolt up to xj driveshaft) - so I can put that 8.8 in , in a day, but I am not comfortable with setting up the front gears - I want more time available so will do in the spring.

What are the thoughts on using FULL TIME AWD with the selectrac tcase with 3:55 up front and 4.10 in back? I'm not stupid enough to be in AWD all the time, or at all on pavement, but let's say I get stuck on a snowy road - wouldn't the selectrac 'absorb' the difference between the front and rear axle speeds? seems to me that the AWD position still allows full differential action between front and rear so it shouldn't really matter if the gears are the same?

I'm not talking about wheeling it like that, just what if the back tires are on ice and I need that extra little oomph to get clear...?
Chances are pretty slim that I would need to do that as the 8.8 is lsd....

I would think you should be fine in an emergency type situation, thats why it has a center differential to keep the front and rear from binding.

I'm not an expert though so no warrenty implied!

Thanks for the .02 XJBob.

One thing that bugs me is that I don't know what kind of diff the np242 tcase has. A spiders/carriers type open diff like in an axle housing can rotate at different speeds all the time IMHO with no damage. I don't think there is a spider/carrier type diff in the np242 so without knowing that....

I was looking through the shop manual for my XJ the other day and I didn't see any parts that look like a spider gear differential in it so I don't know how it actually works either.

I did find an exploded diagram of the 242 on the net and it shows the components but still can't figure out what makes it work.

I do know that my jeep will not move in 4wd fulltime with the rear driveshaft pulled, my t/c output yoke just spins, found that out after installing a sye and waiting for my shaft to be made up.I would not hesitate to run it in full time mode, on loose,muddy or snowy surfaces. (get ya out of a jam anyways)