After hearing what I thought was the end of the world coming from my diff. while doing a U-Turn I was informed that I might want to put the additive in my 10 bolt. Of course this was pulling into the local street meet!! ALWAYS a PLUS.

Anyway, is it a must to clean out the old crap or can I just drain and fill? This is a brand new build, Eaton 3.55, supperior axels 8.5 10 bolt. What do you guys suggest? It's draining now. 620 miles of mild break in b/c everything is new.

Drain and fill and don't forget the possi additive.Try it and go from there.

Agreed. After replacing fluid, drive to big parking lot and do several lock-to-lock figure-8's to distribute the additive about the clutches & plates.

Thanks guys, I'll give that a shot. I didn't see the need to take the cover off either.

If the oil only has 620 miles on it then you shouldn't need to change it. Just get about 4 ounces out and put the additive in. Did you not use any of the additive when the rear end was built?

big head - no I did not put it in originally. Drained and refilled with additive did the lock to lock figure eights for a few minutes and took for a stop and go with lots of slow tight turns and haven't heard anything yet. Thanks again guys.