Originally Posted By: Jim Allen
I was told by a former Dana drivetrain engineer that too much LSD additive effects the viscosity and decreases oxidative resistance of the oil, that is resistance to oxidation from heat. Too little, of course, causes chattering which in turn wears the unit out prematurely or breaks it outright. He suggested that the best procedure is to use as little as it takes to eliminate chatter and no more, but you have to experiment to find that point. Each oil has slightly different friction characteristics so each may need more or less additive.
That process involves extra effort, which is why not too many people do it. It's outlined in some manuals, though it's more common to see, "Add X-oz." The one time I did it the hard way, it took me the better part of an hour. Starting with a newly installed plate-clutch type LS. I filled the axle to about 90 percent and located a parking lot near my home. With no additive I went to the parking lot and did some tight figure 8's in both directions, with a little power on. Chattered like a big dog. I added about half a bottle of the Ford additive and did some more figure 8's. At first it chattered just as bad, but you have to work the stuff into the unit and mix it well with the oil. After a little while, the chattering lessened considerably. I added about a quarter of a bottle more and that eliminated the chattering. For then. Later, it started to chatter a little so I added the rest of the bottle and it chattered no more. The instructions with the unit said to use two bottles, but I don't recollect their capacity in ounces, so I used half that.
I have a new cone clutch style LS now and since it was installed by the mfr., they installed their recommended amount of additive (two bottles). No chattering at all (cone clutches are somewhat less prone to chattering but they still do). When I change out that oil, I should probably have it analyzed to see if it's sheared a bunch and oxidized a lot. If I remember to do it.
Great repsonse, Thanks!