FYI Diffs
I have pretty much ran everything thru these diffs to get them to feel smooth and I'm still looking for the magic formula. I've used lapping compound, tooth paste, polishing compound, ran them on the track, chucked them up in a drill press and let them run one direction and then the other for a hour........gone as far as wore out one casing running anything I could think of only to still not get that silky feeling diff.
Here is part of the problem if you use the lapping compound, the gears are steel and the shaft is hard coated aluminum, as you run it more and more the aluminum shaft gets worn more on the torque end of the shaft and then the gears get sloppy on the shaft. The plastic hub section of the diff housing also starts to wear and again the output shafts will start to wobble as this wears out.
You can run without any of the shims, big ones or the small ones, but as the gears break in the lash opens up and then the potential for them to jam up and lock the diff exists. Since we really don't have a reliable way to check the backlash when the diff is assembled its really trial and error. I have some diffs with no shims, some with either just the large or the small shims, and some with all the shims in. Some feel tight, and some feel less tight, but they all feel notchy. The only time they feel better is as I go up in thickness of diff fluid, where a diff with 700 will have not as much drag feel, but still have a notchy feel to it. The same diff, going to 2000, will have more of a drag feel, but the notchy feel is much less.
I start to wonder if some of the issue is that the silicon diff fluids we use are too good and don't provide enough stick to the face of the teeth of the gears, so we don't get that cushion that we seem to need to get the diffs feeling better.
I also tried the Xceede plastic gears in the diff using the stock big gears, so I could use the stock outdrives, they only lasted one run. If I where to do this again, I would run this setup with all the shims in, as I think the only reason why I wrecked the plastic gears was because the lash was too big without the washers.