I have a 2007 5.4 f150...heres the problem...when i go from 0-40km the rear end chatters then stops, Had the rear diff fluid just changed a few days ago and additive put in as well, Mechanic tells me has to be driven a bit to work the additive in to the clutches....I have put approx 300kms on it since the diff oil was changed and its still doing it, how many kms does it take to work this additive through?? Any other suggestions on what the problem may be would be appreciated....Thanks guys...

 

my clutch packs in my 07 screw did the same thing but only from a stop to a turn. need two bottles of motorcraft friction modifier with gear oil change. if may go away, it does take a lot of driving for it to work.