Good question. Some of the shop manuals call for lube weights that aren't made anymore. You can either use a weight that is the closest to what your book calls for, or experiment. I've tried straight 90, 80W-100, and 90W-140. I find that the heavier weight oils reduce the gear clash and "spin-down" time noticably. However, if you use the heavier oil, the tranny acts "gummy" or can be slow to shift when cold. This would prolly be worse at 40 degrees F or below during the winter. But its OK when the box warms up to operating temp. Let us know what works for you.
Chip
