C2 transmission drain plug leak

[Richard S.]

I have a 63 340 HP car that leaks at the transmission (T10) drain plug. I thought some time ago I saw an article that this may be caused by the newer type of transmission fluid used. If this is the case what was the original type of transmission fluid and is it available.

Thanks
Rich

[John F.]

Re: C2 transmission drain plug leak

Get some plumbers tape and wrap a few times around and good to go.

[Richard S.]

Re: C2 transmission drain plug leak

John
Thanks for the response. Actually I noticed a number of potential remedies from posts of several years back. I am not sure how the tape would hold up over time (long or short) with additives in the gear oils. But I did find an interesting article in an old Corvette Restorer issue. You might find it interesting. Take a look at an article written by Jeff Blakeslee Spring 2015. Covers choices to consider in selecting gear oils for C2 vetts. The article was based on research for a Muncie transmission. I have a Borg Warner unit. But in looking at the specs for my 63 car I see a common requirement for gear lube as the Muncie unit, Mil-L-2105B with 80w-90w GL-4 rating which fits what my baseline would be. Choice to some extent depends on car use. Anyway some food for thought. I first need to look back and see what type of gear lube I used last. Tape may still be a choice since I do not see any other leaks, for now.
Thanks again.
Rich

[John F.]

Re: C2 transmission drain plug leak

I also use the plumbers tape on my Model-A trans & rear differential.

[Duke W.]

Re: C2 transmission drain plug leak

John
Covers choices to consider in selecting gear oils for C2 vetts. The article was based on research for a Muncie transmission. I have a Borg Warner unit. But in looking at the specs for my 63 car I see a common requirement for gear lube as the Muncie unit, Mil-L-2105B with 80w-90w GL-4 rating which fits what my baseline would be. Choice to some extent depends on car use. Anyway some food for thought. I first need to look back and see what type of gear lube I used last. Tape may still be a choice since I do not see any other leaks, for now.
Thanks again.
Rich

By '63 the spec was Mil-L-2105D. The mil spec was cancelled and replaced in the seventies by the commercial API spec 89W-90 GL-5, not GL-4 and this same spec gear oil should be used in axles with the proper friction modifier additive if the axle is Positraction. I don't think GL-4 existed back in the day, so the 2105D equivalent of modern GL-5 was specified for both axles and manual transmissone, but most modern manual transmissions specify GL-4, which lacks the EP additive necessary for heavily loaded hypoid gearsets in axles.

So is GL-4 okay for our old transmissions that originally specified the equivalent of modern GL-5? I don't know because I've never seen any rigorous durability tests of GL-4 in these old transmissions, but I am convinced that you can't go wrong with GL-5. and DEFINITELY DO NOT use GL-4 in vintage Corvette axles.

As far as your leak is concerned those tapered NPT threads should seal. Synthetic oils reputedly have more tendency to leak, but I wonder if there might be a small crack near the drain plug. I don't know if Teflon tape will resist the oil, but I'm sure a film of something like Permatex #2 will seal. Don't overtighten that plug - maybe 15-20 lb ft. and the Permatex is non-hardening so the plug should come out if ever necessary, but a fresh fill of GL-5 should be good for at least a couple of decades in typical vintage Corvette service

Duke

[Joe L.]

Re: C2 transmission drain plug leak

John
Thanks for the response. Actually I noticed a number of potential remedies from posts of several years back. I am not sure how the tape would hold up over time (long or short) with additives in the gear oils. But I did find an interesting article in an old Corvette Restorer issue. You might find it interesting. Take a look at an article written by Jeff Blakeslee Spring 2015. Covers choices to consider in selecting gear oils for C2 vetts. The article was based on research for a Muncie transmission. I have a Borg Warner unit. But in looking at the specs for my 63 car I see a common requirement for gear lube as the Muncie unit, Mil-L-2105B with 80w-90w GL-4 rating which fits what my baseline would be. Choice to some extent depends on car use. Anyway some food for thought. I first need to look back and see what type of gear lube I used last. Tape may still be a choice since I do not see any other leaks, for now.
Thanks again.
Rich

Rich-------


Neither teflon tape or most sealers will be adversely affected by the transmission lubricant. As a matter of fact, teflon tape, a non hardening sealer, or anti-sieze should ALWAYS be used on these transmission plugs. Otherwise, galvanic corrosion between the aluminum case and steel/iron plug will cause the plug to seize in the case making its removal next to impossible. These plugs are notorious for this.

[Leonard M.]

Re: C2 transmission drain plug leak

GL-4 vs GL-5 and synthetic. "The Difference between GL-4 and GL-5 Gear Oilsby Richard Widman"
This explains a lot.
Transaxle_oil.pdf (widman.biz)
This lube is a safe bet.
Sta Lube GL-4 85W90 Gear Oil - 1 qt SL SL24229 | Buy Online - NAPA Auto Parts (napaonline.com)

[Harry S.]

Re: C2 transmission drain plug leak

This is what I use in my 63.

IMG_2414.JPG

[Richard S.]

Re: C2 transmission drain plug leak

Many thanks John, Duke, Joe and Leonard for the information. I will try using one of the sealers on the plug and see if the leak is stopped. I will give it a try and have a look in the next few weeks and see if the hot NJ weather brings on any leaks.

Thanks again
Rich Sheridan