Thunderman: I am not sure what the stuff is, I just know he used a squirt bottle to put it in. He put several ounces in then filled the differential with oil. When I was younger Hudson automobiles had a "wet clutch" in them and the liquid that went in them was like a ground up cork in a mineral oil base. What ever it was, it stopped the shudder on my truck. I kind of imagine all truck "limited slip" differentials have something comparable.
