Sooo..... I just swapped my transmission for the third time since I've had the truck, the last one was supposed to be good, but jumped out of first (making a clunking noise that would make the angels cry) and leaked like a seive. Installed a tranny today (R150f I believe) out of an 87 or 88 4runner and now I can no longer shift into 4wd while in motion. I also installed new 4.88 diffs out of a 93 runner, 4wd works fine just will not shift on the fly. Any Ideas???

 

If you have ADD, then the ADD will disconnect the other side of the diff, and send all motion from the passenger side tire into the drivers side.

Maybe your ADD was stuck on the old diff?
Make sure that your 4WD kicks on the ADD when you stop and put it in 4hi

 

ADD is working fine, 4wd light comes on, just can't shift into 4wd unless I come to a complete stop... I'm thinking that the transfer case is just not built for shift on the fly as it is out of an older runner... Might try changing it if I find the motivation, but I just spent the last 4 days covered in grease under my truck, so I'll probably drive it as is for a while.

 

You need the right combination of differential and transfer case to be able to shift on the fly. If you look in the FSM you will see that the transfer case for the ADD option has an extra synchro in it to help the shifting since the ADD locks in after the transfer case. On a truck with manual hubs this synchro isn't needed since the front diff and drive shaft to the transfer case will already be spinning with the hubs locked. I have had the same problem after I had my transfer case swapped a few years ago, and I now have a new one sitting in my driveway waiting to be swapped in again.