Can anyone tell me why rear tires chirp when turning sharp in 4wd mode on dry pavement? Know you are not supposed to do it, but how does rear posi differential even know vehicle is in 4wd ?????????? seem like it should just slip like on any other sharp turn??????

 

Because they are not turning at the same rate as the fronts - something has to give. Do *NOT* drive in 4wd on dry pavement and turn the front wheels - period. The transfer case is locking the front and rear driveshafts together.

 

The front diff and the rear diff are going to rotate the exact same of revolutions. When cornering the rear tires take a slightly shorter track than the front tires (I think, please correct me if I am say something stupid) the difference in the distances driven between the front and the rear require give in the driveline, which won't happen. The give occurs at the pavement with the tires rubbing on the pavement... thus chirping

 

Thanks, i see it now. On a tight turn the rear inside doesnt need to go nearly as fast as both fronts.!!!!!!!!!!!!!!. Transfer case sort of sets a minimum speed for rear end that the differential can not handle??

 

oh the transfer case can handle it, for a while at least. The tires typically give first, hence chirping

 

First off, why are you turning sharp in 4x4 on dry pavement? Why are you using 4x4 on pavement at all? It is not all wheel drive, it's 4 wheel drive.
When you turn, the front end has to travel a longer distance than the rear end, as the rear is trailing behind on the inside of the turning. This means the rear tires would be turning slower. In 4x4, the transfer case mechanically locks the front and rear together so they turn at the same speed. Turning on pavement in 4x4 binds up the gears in the transfer case. When it starts to bind, everything starts to twist and take stress, including the chain in the case, the driveshafts, and the axleshafts. The bend up and twist until something breaks. Fortunately for you it is normally the tires. Do this enough and it will soon be something else. U-joints, axles, CV joints (most likely).
You should ONLY use 4x4 on surfaces where the tires will slip.

If you don't know how this stuff works, here is a basic description
http://auto.howstuffworks.com/four-wheel-drive.htm