I would like to know were you add friction modifier to the rear housing on my ford FX 4x4 04, it was purchased at dealer, I think it goes in the side of the rear end housing. I saw a video showing a plug on a 2002 but could not see one. Just dont want to do it wrong.

 

If you look where the input shaft goes in from the drivers side of the truck, looking at the front of the differential, there should be a plug there above the casting lip. Why are you adding the friction modifier? Did you change the fluid or are you wanting to add more friction modifier?

 

Thank you for answering, there is a chadder from the rear end when you are turning from a dead stop take off.
The mech. at the dealer told me that the limit slip is sticking and by adding this it will stop this.