[427sharpe]

I saw your post, didn't know an answer so I called my FoMoCo Motorsports Rep, and HE says the "Friction Modifier" is a compound agent (which means he doesn't know what the he!! is in it either) to lessen gear chatter and reduce NVH (noise, vibration and harshness) as well as to displace moisture, which can cause trouble in locked or posi rears. He said this was a real problem a few years ago w/ trucks that lowered boats into water (imagine that!). He said a lot of the race teams DO use it in the 9" Lockers, but he said most don't because they either change the fluid or the pumpkin between each race. An interesting aside is that Ford requires it at differential service intervals to maintain warranty.