Hi all tech folk, and thank you for weighing in on this quandary! I've owned my 2000 Corvette for about 2 months now (it has 89k miles on her), and just recently discovered a small fluid/oil stain in the rear passenger side of the car. It appears to be only a few drops of "oil" (blackish brown, smells like petroleum). I crawled up under the car and checked for the seals on either side of the differential, but it appears to be dry on the sides. I just finished installing new brake rotors and tires all around the car, so I thought perhaps I "wrenched" something loose? Nothing seems to be oozing or wet at the brake lines. The fill port at the rear of the differential is dry, and still sporting its metal tag!
-However;
The drain plug area of the differential has what looks like a spray pattern around it, and the oil seems to have travelled down the to drip off onto the floor. I wiped it down as best I could, and found that it only leaks when it's been driven (put under pressure).
I reached up and felt for the vent post, and found it could be turned in its "socket" or seat, but not able to pushed down.( I don't think it should be able to be pushed in, but maybe I'm wrong?)
I have scoured the service threads for just such a problem pertaining to the drain plug failing, but have come up empty.
So, I'm thinking that I shall drain the differential, put some plumber's teflon tape around the threads and refill with some Mobil One synthetic 75w-90 gear oil.
Is there anything that I can consider doing before attempting the diff oil change?
Your expertise and insights are very much appreciated in this matter!

 

Some Corvettes have what is called a "leaky butt".
Info when you Google "leaky butt Corvette"

 

Don't put teflon tape on the drain. There is a sealing washer on the plug, similar to what you find on the brake line banjo fitting, that someone might have over tightened. There is a torque value for installing this plug. The other thing to check is the front of the differential where it mates to the transmission. Sometimes that joint will leak, and if its leaking, it could blow back and could collect in that area.

 

So I'll be replacing that drain plug instead of "taping" it, and I'll definitely check the front for seal failure.

 

Hardware store.....nylon washer..

 

Actually, I believe it is aluminum. Original part # was 12369215 for the sealing washer, but it may have been superseded at this point.

 

100% The first thing to check would be the ALUMINUM sealing ring on the drain plug. They often stick to the diff housing when you first remove the drain plug and then fall off into the drain pan when you are not looking! LOL!
Try tightening it to the proper torque spec. Just replacing the ring would be the correct next step if it already is properly torqued.

DO NOT use Teflon tape!!!!!!!!!!!!

IF, you decide to get a new drain plug, find one that has a magnetic option. They will be AFTERMARKET. Nice addition!

On the diff refill, get the proper lube with the GL-5 additive or get the lube without the a limted slip additive in it and add your own!

NOTE!! ALWAYS loosen up the diff fill plug before you remove the drain plug. If the fill plug is stuck and cant be removed, you cant refill the diff!!

When you remove the fill plug or drain plug (when the differential is cold) there is "SUPPOSE" to a slight vacuum on the case. You should hear a very slight inrush of air when the plug is first removed.

That VENT has a small rubber seal in it with small spring a on top of the seal that lets pressure out but is supposed to seal on cool down and allow the diff to build a slight vacuum. YES, the vent cap will be loose. Its there just to keep dirt out of the vent!

Bill

 

Thank you, Bill, for the clarification and the tips! After crawling up under there a bit more and feeling around, I think the culprit is, as VetteNuts mentioned, further up at the transmission/differential joints. Would you happen to know a general ballpark figure for getting this repaired?
I just need to know if I should sell a kidney in the near future !

 

Yes, it is an aluminum washer. Try a nylon one.

 

I do ALL my own work. So, its difficult for me to quote shop prices. It will not be inexpensive!!

Why cant you do it your self?? Its really not that difficult. Got friends with a garage or shop??
Recommend that you wipe the entire diff and trans down and take it for a quick drive. Reinspect. Then let it sit over night and recheck in the morning. That will give you a better idea on where the leak is actually coming from and how much its leaking.

Recommendation! .Pull the fill plug and see how much below the fill plug hole the level is. If its not leaking too badly, you can top it off with some 75/90 GL5 and decide what you want to do. Just add lube till it runs out of the fill hole. DO NOT try to add any more.. Listen for that little WOOSH of vacuum when you pull the drain plug.

That will buy you some time so you can also do some shopping around for a good dependable C5 garage in the area if you can not do the repair your self.

Bill

 

Thank you, Bill, I will indeed get the affected area wiped down, then check the fluid level. It's consistently two or three drops about nickel size, and only after the car has been driven, so it's not a full time fluid-loss.
I live near a local Corvette-specific shop called Restoration Station (they do a Fall tour each October), I'll see if they can help out.
Many thanks for your help!!

 

Edmund Iverson, forgive me for hijacking your thread but I have short "related" question--why not use teflon tape?

Thank you.

 

Bill, would you happen know the thread size for the diff drain plug?

Thanks,
Jim

 

I do not have that info on hand. Sorry..

 

Thanks, no worries.
The general consensus seems to be: Differential metric 20-1.5

Jim

 

Teflon tape is used in situations where the threads do the sealing (such as a pipe thread). This drain plug has a washer that does the sealing, so Teflon tape on the threads won't help, but could lead to the tape getting inside the diff where you don't want it.

 

I think it's a valid question, and I'm glad you asked it! And Walt G, thanks for answering!

 

Were you able to find the source of the problem and fix it?

 

The leak has "gone away", as ridiculous as that sounds! I jacked up the car, sprayed brake cleaner all over the area (it really needed it!) and waited to see where the leak would reappear. It never did! I'm not complaining, but it was a mystery leak that I hope doesn't come back.
I think I may have torqued a seal while I had it jacked up for the brake replacement, and as the car settled, so did the seal? Overall, I'm grateful to have a dry rear end!

 

Sometimes a leak is only while car sits overnight, other words it is related to the temp of oil. I see your first post was in May(maybe garage was relatively cool over night). Your last post is August. Just a thought, I have this same thing with my 2000.