2. Obviously, the old rear cover needs to be removed and the gasket surface and gear area cleaned thoroughly. A gasket scraper followed by some Scotch-Brite took care of the gasket surface. We used a few cans of brake cleaner and some rags to wash out all the old fluid. While we had access, we inspected the gears and Posi unit, which all checked out. We knew this car is equipped with some low rear gears, but we were able to get an exact ratio by counting the teeth on the ring (41) and pinion (9) and then dividing the ring number by the pinion. Ergo, 41 divided 9 is 4.55555556 or 4.56:1.