From time to time we get questions about what oil should be used in the manual transmissions and axles of our vintage Corvettes. Needless to say the recommendations in the old service manuals is esoteric to say the least. For example, the transmission and axle lubricant specified in the 1963 Corvette Shop Manual (Note 2 page 0-7) says: "Lubricate with SAE 80 or 90 Multi-purpose Gear Lubricant meeting requirements of U.S. Ordnance Spec, MIL-L-2105B." So what the heck does this mean?
If you go to www.api.com , the web site for the American Petroleum Institute, which promulgates lubricant specifications, you can find the answer, but I'll summarize it here. Both the general requirements and type of service for motor oils and gear oils are listed and can be printed out for reference.
Under the GL-5 specifaction it reads in part: "Lubricants qualified under the U.S. Military Specification MIL-L-2105D (formerly 2105C) satisfy the requirements of GL-5 service designation..." The spec listed in my shop manual is just an older version that was current in the early sixties.
So the bottom line is that you should install a GL-5 oil in both the four-speed transmissions and axles that specify MIL-L-2105, and either the traditional 80W-90 or newer 75W-90 weights should be used. Of course, if you have a positraction axle, the GM additive should be used unless the lubricant manufacturer specifically states that the friction modifiier additive is already included.
FYI, the GL-3 and GL-6 specifications are considered to be obsolete. The API web site is listed below if you would like to view or print the gear and motor oil service specification charts.
Duke
If you go to www.api.com , the web site for the American Petroleum Institute, which promulgates lubricant specifications, you can find the answer, but I'll summarize it here. Both the general requirements and type of service for motor oils and gear oils are listed and can be printed out for reference.
Under the GL-5 specifaction it reads in part: "Lubricants qualified under the U.S. Military Specification MIL-L-2105D (formerly 2105C) satisfy the requirements of GL-5 service designation..." The spec listed in my shop manual is just an older version that was current in the early sixties.
So the bottom line is that you should install a GL-5 oil in both the four-speed transmissions and axles that specify MIL-L-2105, and either the traditional 80W-90 or newer 75W-90 weights should be used. Of course, if you have a positraction axle, the GM additive should be used unless the lubricant manufacturer specifically states that the friction modifiier additive is already included.
FYI, the GL-3 and GL-6 specifications are considered to be obsolete. The API web site is listed below if you would like to view or print the gear and motor oil service specification charts.
Duke
