C2-C3 Trans & Diff Lube capacities

[Wayne M.]

I have checked the archives an see multiple references to Duke W.'s "3 pints for the Muncie trans and 3.7 pints for the diff".

But my '65 Owners manual and shop manual call for 2.5 pints for the 4-sp trans.

Chilton's '63-72 Repair & Tune-up guide shows Trans at 2.5 up to 1965; then 3.0 pints thru '72. Can it be that the case volume changed from the 3831704 ('63-only) and 3851325 ('64 and '65 cases) when the '66-67 3885010 case and the subsequent "660" and "661" cases were used ?

With the differential, all sources point to 3.7 pints up to the end of model year 1968; then 4.0 pints is shown in the Chilton's source up to 1972. [I don't have '67-up GM capacity sources to X-check].

Also, I see that GL5 gear lubes may contain sulfur-based compounds to meet the "EP" extreme pressure requirements of the differental hypoid gears, but some say never to use these in our beloved Muncies, as the brass synchro rings will be attacked. Opinions ?

[Duke W.]

Re: C2-C3 Trans & Diff Lube capacities

I don't recall ever saying 3 pints for the 4-speed. The capacity in the 1963 Corvette Shop Manual is listed as 2.5 pints, and that's what I believe I've always quoted. I've seen enough to conclude that I get misquoted more often than accurately quoted.

The original manual transmission oil spec was Mil-L-2105D, and the current commercial equivalent is API GL-5. In fact, the mil-spec was cancelled a few years ago and the military now uses the GL-5 spec.

The "sulfur attacks brass synchro" material is overblown hype and myth IMO. Yes, there is evidence that this can happen, but it's at very high temperatures - beyond what your transmission will ever see.

Have you EVER read any reliable reports that a transmission tear down revealed "corroded synchronizers"? I haven't!

My recommendation is to use what GM recommends in these old design manual transmissions - 80W-90 GL5.

As far as the axle is concerned, the book quotes 3.7 pints and since the axle design was the same through 1979, I doubt if it changed.

The best source of specs is GM material - shop manuals and AMA specs. Yes they have errors, but if they corroborate, they are usually accurate. Third party sources like aftermarket shop manuals are the least reliable sources for technical data. They can generate their own errors in transcription from OEM material, and if the OEM material is wrong it will also usually be wrong in the aftermarket sources.

Duke