Spent a couple of hours last night and again this morning reading what I could find or understand about gear oils. To say the water is muddy would be an understatement.
I just can't find a solid reason for not using the same multi-purpose "gear oil" in a standard differential or standard manual transmission. Other than using a 80W-140 or 75W-140 synthetic in the transmission may cause it to shift a little stiffer when its cold because it's a heavier viscosity. As far as the lubricating properties in a transmission it sounds to me like it would be over kill if anything.
All of the Chevrolet Shop manuals even a way back 50 or 60 years ago OK the use of 90 weight multi-purpose gear lubricants in both the differential and transmission.
I mean I've run the plain old 80W-140 I’ve gotten from the Farm Supply stores in both the differentials and transmissions for most of my adult life and never seen a problem with it.
Anyone out there have a logical answer to this??
Denny Graham
Sandwich, IL
