Fred,
Actually, I think there are sulphur compounds in the Hypoid lube that attack the bronze bushings inside the tranny...
At least, this is what I THINK I read on the AACA website....
Have always read SAE 80-90 for the manual truck tranny....and whatever you're putting in the rear end should have an EP rating ("Extreme Pressure") for the hypoid ring & pinion.
The ONLY antique trannys I've ever seen use less than gear lube were the Chrysler semi-autos that used SAE-10 oil.
If some rebuilder tells you "light oil" is okay in your 'Bolt's tranny, ask him if he'll give you a warranty on the tranny which will include free rebuild-replacement for at least 50,000 miles!
