So, I just acquired a 04 expedition and Im trying to learn the vehicle specs. In doing so I ran across the need for a friction modifier in the LS rear ends. Can some one explain to me what this is and if there is a reputable equivalent that I can get from somewhere like Autozone or O'Reily's?

Also, how can I determine if I have a LS in mine. It is a 04 Exp. 4x4 5.4L 16V EB.

Would this modifier be needed in the front diff, tranny or x-case as well?

 

Look on the driver side door for a sticker with vehicle info on it. You will see a place where it says axle code. The codes are

17 = 3.31 non-limited slip
19 = 3.55 non-limited slip
H6 = 3.73 limited slip
H7 = 3.31 limited slip
H9 = 3.55 limited slip

If you have limited slip you will need the friction modifier. Only for the rear end as the front axle is open. You can get some stuff called trans-x at the local auto parts store but it's better to get the Motorcraft friction modifier IMO.

 

Do you know whether or not XL-3 or XL-7 is used or is XL-3 obsolete due to XL-7?

Also, my manual show 75W-90 and I have been reading that that has been changed to 140, maybe...is that right?