What friction modifier is best to use?

[toomnymods]

I bought 3 quarts of Amsoil Max gear lubricant yesterday to use in my rear diff and was wondering what friction modifier where you guys having the best luck with?
Amsoil friction modifier

or


Ford Racing's Friction modifier

and how much did you add?

 

[Norton]

I went with 4oz of Amsoil Slip Lock.

 

[UnleashedBeast]

Both are great. It's one of the few products Ford supplies that I really like. Using either, I prefer to use half the bottle or tube, then test. If no chatter is present, do not use the rest. If chatter is still present, use the rest.

I test by rolling the windows down in a parking lot, turning as tight as possible, very slow. Try this in both directions. You will hear the rear differential making noises if there isn't enough friction modifier.

Since I didn't have any Amsoil Slip Lock on hand for my last differential oil change, I had to buy Ford's XL-3. It worked like a champ with Red Line Heavy Shockproof gear oil. *Used it to assist with gear whine*