Read diff small leak
Thread Starter
Heel & Toe
Joined: Aug 2020
Posts: 17
Likes: 1
Read diff small leak
Hey guys question. I’m doing a restore on my 78 and the rear differential has a very small leak. Not noticing anything on the floor but the right side of the diff is a little wet. Seems to be from the filler plug area. The plug is tight and There is no gasket on the plug just a red plastic tag telling you to use limited slip fluid only. I see a few corvette sites that sell a gasket for the plug, is it supposed to have a gasket? I don’t see how that would even work and the plug doesn’t seat on anything. Seems to be just thread sealed.
I guess I’m not 100% sure it coming from the plug but that’s the areas that seems wet. Its a very low mileage car with originals fluids, gaskets etc and I really don’t want to Pull the diff apart but I also don’t want the leak to get worse. Any thoughts.
I guess I’m not 100% sure it coming from the plug but that’s the areas that seems wet. Its a very low mileage car with originals fluids, gaskets etc and I really don’t want to Pull the diff apart but I also don’t want the leak to get worse. Any thoughts.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
I don't see how a gasket would work. But if its on the internet, it must true, right?
Like you say, the red POSI tag is loose, free floating. No gasket needed, its a NPT.
With the rear up on ramps, you can use an open-end wrench and remove that plug. I would recommend two things. Using a white pipe cleaner as a dipstick, you check the fluid level. Next, when done, smear a dab of thread sealant on the last few threads of the plug and you are good to go.
Like you say, the red POSI tag is loose, free floating. No gasket needed, its a NPT.
With the rear up on ramps, you can use an open-end wrench and remove that plug. I would recommend two things. Using a white pipe cleaner as a dipstick, you check the fluid level. Next, when done, smear a dab of thread sealant on the last few threads of the plug and you are good to go.
Last edited by HeadsU.P.; Aug 23, 2020 at 05:09 PM.
Thread Starter
Heel & Toe
Joined: Aug 2020
Posts: 17
Likes: 1
I was going to try sealant On the threads. Was thinking I might remove the lower bolts one at a time and put some sealant each one as well. Seem it could be seeping from there too. Not a lot and diff levels is good. Love the pipe cleaner trick. Thanks
Thread Starter
Heel & Toe
Joined: Aug 2020
Posts: 17
Likes: 1
Agreed my car is on a lift and level. The leak on mine is very minor, probably shouldn’t worry about it, but I’m a bit of a perfectionist. Thanks for the help guys. Going to try thread sealer on bolts and some pipe tape on drain plug. If it happens to be the gasket I will will live with the leak, not going to rip into the diff
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
You are restoring a 78 and not going into the original 78 diff? If original you should, they had soft axles, loose RG bolts, and lousy clutches.
The fill plug is a 3/4 npt thread so just a little #2 permatex is all you need if it is leaking there and not from the axle grinding into the axle seal causing a leak. You should look close to see.
The fill plug is a 3/4 npt thread so just a little #2 permatex is all you need if it is leaking there and not from the axle grinding into the axle seal causing a leak. You should look close to see.
Thread Starter
Heel & Toe
Joined: Aug 2020
Posts: 17
Likes: 1
Axle seals dry. Car has 7k original miles on it. Not planning to race it. Freshening up body and suspension and taking the 197hp motor out and putting in a 350hp crate motor. Looking for a nice weekend driver. Not a show car or race car.
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,939
From: Connecticut, USA
The issues I mentioned are common to the mid to late c3's doesn't matter about mileage as there were issues from day one. With that said all I can say is good luck. You will know in time if the axles are wearing down or a RG bolt backs out.
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Burning Brakes
Joined: Jun 2020
Posts: 881
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FWIW, GTR1999 (Gary Ramadei) has long been regarded as top expert on corvette differentials; he rebuilds & improves them for folks from all over. Just sayin'
Thread Starter
Heel & Toe
Joined: Aug 2020
Posts: 17
Likes: 1
Appreciate the feedback especially Gary’s opinion. I’m a newbie to the forum but not old vettes although admittedly this is my first layer model C3. My 70 has lots of miles and no diff issues. Sounds like however the later C3’s do. My question/ problem is this. I’m attempting to do a mild rebuild and was hoping to do all/most of the work myself. Tearing apart the diff is beyond my skill but more importantly tool capability. With that said I’m replacing all the suspension and brakes. Going for a mild upgrade over stock. Like I said don’t plan to race or show this car. Just want a nice weekend car that I don’t have to worry about and it’s sounds like I may have to worry about the diff so perhaps I need to rethink that plan. Gary, can you help me out?
