Join Date: Dec 2010
Location: Epping, NH
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You won't need it in the front. No such thing as a stock limited slip differential in the front of any Ford 4X4.
As far as the LSD in your back diff, You might want to just change the oil and drive it. The limited slip additive balance is the key to effective operation of the limited slip diff. Too much and the clutches will slip when you don't want them to, not enough and you will get "chatter" when turning corners. Don't take anyones word for how much to use if you want the best out of your limited slip.
Change the diff oil, add nothing. Drive the truck for a hundred miles or so (not continuously). After getting the miles on, you know the oil has been all the way through the clutch pack. Now, after running the truck for an hour or so, come to a complete stop. Turn the wheel full lock in one direction and slowly roll into the throttle. You want to be moving between 1-5 MPH. Do you feel the chatter? The truck may actually shake. If you do, to start, add 2 ounces of the additive (by removing the ABS/VSS sensor on top of the diff). Drive it for about 50 miles (or a few days) and try the same thing again. Add only one to two ounces at a time. When you do not have any chatter, your done. Do not add any more.
Many of the synthetic diff oils (Lucas, Mobil1, Royal Purple) do not require the additive, but again, if you feel the chatter and it bothers you, add an ounce or two.