As you know I am not a genius at any of this, but when I installed my limited slip rear end it would jump or feel like it caught when turning. I contacted the place where I bought the rear end to ask for help and they told me that you have to add the "additive" to keep it from locking up. I did and it helped immediately. Had to buy the additive from Ford. Again, I am not going to act like I know why, but it works. Larry