I own a Losi JRXS-R that I will be fielding at the IIC this year, and the diff is giving me fits. As we all know touring cars with front spools and rubber are incredibly sensitive to the rear diff action, and this one is no exception, the change in drivability is massive over a tiny adjustment in the tension screw. My problem is that I have built diffs for years and years, offroad, 1/12 scale, and all of them work just great, but for this car in order to be sufficiently loose to have good rear traction it slips under power, and badly. I have run new smooth and sanded rings, broke in rings for what seemed like silly amounts of time (made little difference), steel balls, carbide, and now pure nitride balls, but nothing I do seems to keep the diff from slipping without being almost locked and having to Tokyo Drift my way around the track (fun, but not very fast).
So basically, what is the Touring Car Ball Diff secret? As far as I can tell I have to run the diff dry, or with half of the usual number of diff balls, to get it to hold while still giving me enough diff action.