1998 Dodge Dakota Backwheel locks when I switch to 4x4

Are you doing this on pavement?

I think it locks completely anyways. But yes, on pavement or concrete inside the parking garage the rear wheel screams loud because it's locked..

That is somewhat normal. When you place it in 4wd, it should be on a surface that is slippery because the wheels are all locked in. If there is no give in traction, the system fights itself because when you make sharp turns, the inner wheel turns slower than the outer ones.

So what your'e saying is that the "wheel lock" will go away if I just switch to 4x4 when it's slippery? Or will the wheels always lock on pavement etc and not when it's slippery?

I tried it right now. I switched to 4x4 on regular tarmac. Then I was driving slow and took a 90 degree turn, and the rear wheel lock's..

The 4wd will fight itself on a surface where the tires get traction. As far as the a total lock up, chances are something will eventually break. However, the only other thing that could cause a lock up as you described is if tire size from front to rear is different, axle ratio has been changed and are different in the front and rear, or the differential itself is bad. However, you mentioned it doesn't do it in 2wd which leads me to believe it is caused as a result of the 4wd being engaged on dry pavement.

I have an expedition. It has A4wd. But, if I place it in 4wd, it fights the heck out of me when turning.

First, thanks for the positive feedback. Also, let me know if you have other questions.