Kubota B 8200 track lock rear end

I have a late 80s Kubota B 8200, the rear like to lock up when making a turn to the left or right I have disconnected the heel peddle for the rear and lock up everytime you go to make it turn it'll make the front end skid to whatever direction your steering too. when turning you hear a pop sound from the rear diff and then you'll be able to make a complete turn.

Does anyone have any idea what is going on in the rear differential of my tractor?