1998 durango grinding in 4wd

My 4wd works in a straight line but as soon as I turn the wheel one way or the other it starts making a nasty grinding noise. Sounds like the ring a pinion gears are just grinding themselves away and it doesn't like to come back out of 4 I have to back up 2-3 car lengths to get it to releace but I don't know what differential it is equipt with and can't find any exploded images to try and use to help me diagnosis this issue if anyone has had to do some front end work and can shine a little light on the subject I would be most greatful.