when i put my 1978 ford f150 into 4wheel drive it feels like i am fighting it. i give it a little gas and go about a foot when it stops and i lay off the gas and it rolls back like it was rocking back and forth. i once gave it more gas when this happened and the rear wheels spun for half a rotation then i let off the gas. the rear driveshaft was at a higher angle and looked like it was about to snap at the axle. the axle normally is about at a 15-20 degree angle but was almost 45 degrees. when i put it in 2 wheel drive it fixed it self and went back to normal. this only happens when i lock the front wheels and put it in 4 wheel drive. we jacked up the car and when i drove it on the jacks in the air it drove fine. but the front driverside wheel seemed to go then slowly stop and then rotate like the second hand on a clock while the opposite wheel was going fine. i didnt have this problem about a few weeks ago and it used to drive fine in 4 wheel drive. i know it cant be the gear ratio's it just seems when its in the air it is fine but on the ground it doesnt work. i tried two different drive shafts and that does nothing. it starts to go in 4wheel drive then it seems to stop and im afraid that if i give it to much gas i will break the rear driveshaft. i have looked through the books and found nothing. i was told it was a d44 up front with a 205t-case and 9inch in the rear if that helps. its stumped me, my friends, and dad. if anyone might have an idea it would be greatly appreciated. thankyou.
joseph

 

I noticed that you posted a prior related problem about the TCase and I'm wondering what ever happened to fix that problem. Having 1 wheel in the front spin slower than the other is probably normal for an open diff, it could indicate more brake drag or wear on one side, but I think this is near normal.

I'd double check the number of spins that each tire makes as a way of confirming the gear ratio, but from what you've said, it sounds like the truck wont move at all and the gears would have to be very different for that to happen.

Given that, I'd look for a problem with the transfer of power in the front end under torque. Disconnect the rear drive line and hang it with some wire. Put the truck in 4WD then try to drive with front wheel drive only and see what happens. If you can't move in front wheel drive only, somethings wrong with the diff or in the hub area and I'd start checking there. Maybe take apart the hubs and do a wheel bearing job and check for dammage.