took my diff in to get one this avo, spoke to the guy and he showed me how it works. its got two plates which apply pressure via. four springs to each side. with a car that had one fitted up on the hoist he showed us how both wheels spun together unless you put a bit of decent bit of force for them to spin in opposite directions. he said after it wears out the diff will act like open centre, but he said they have improved it and it will now last three or four rally seasons before being wering out.