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The seam between the transmission and differential is prone to leaking with more then stock torque, or if you drive your car pretty hard. In my humble opinion, it appears that is what is happening with your car based on the photos. It could also be the transmission output shaft seal. Identifying whether the fluid is transmission or differential fluid will provide clarity. Definitely not the easiest leak to repair. You’ll have to drop the transaxle, separate the transmission and differential, clean/replace seal or o-ring, and reassemble. Companies like East Coast Supercharging make a support cage that mounts around the trans and diff to eliminate the risk of this happening. I’ve got one installed on my transaxle assembly. No leaks for me to date. Good luck with the repair!
Last edited by wscott62893; Jan 1, 2019 at 08:27 AM.
Here are few oil leak paths on the Trans and Differential mount flange seams. If you confirm one or both these seams are leaking, then it is recommended to remove the Trans from the car for resealing
Cheers,
In my case, the box that the reverse lockout solenoid mounts to was leaking. It's on the top right of the transmission, but the leak trickled down the case and looked like what you posted. I thought it was a rear seal or something, but when I dropped the trans, it was obvious that it was the box that was leaking. Pulled it off, resealed, and it's been bone dry for a few years now.
In my case, the box that the reverse lockout solenoid mounts to was leaking. It's on the top right of the transmission, but the leak trickled down the case and looked like what you posted. I thought it was a rear seal or something, but when I dropped the trans, it was obvious that it was the box that was leaking. Pulled it off, resealed, and it's been bone dry for a few years now.
Is this the box you mean, something up top looks very greasy?
Axle seals. Both the axle seal itself and the side cover o-rings are common leakers.
That looks bad, check the fluid levels ASAP, probably low.
It was transmission fluid when I smelled it, was able to stick my pinky finger in the fill hole and able to get end of finger into fluid, so hopefully that wasn't too low.
I drained it, and am letting it drip out more before refilling with fresh fluid.
What is this part, the black tube looks oily on my car, not sure if the pictures show it.
Thats the part I was referring to. On my car, it was a gunky mess, with a clear trail from it down to the bottom of the transmission. It looked like a leak from the bottom where the trans meets the diff.
That box is just sealed with RTV, I took it off, cleaned it all up, and new RTV along with a new solenoid "while I was there", and no leaking for the past 2 years since. I think this is a more common issue than people think. They're more likely to blame the seal at the back of the transmission, which is WAY more work to "fix". I didn't touch that seal.
Thats the part I was referring to. On my car, it was a gunky mess, with a clear trail from it down to the bottom of the transmission. It looked like a leak from the bottom where the trans meets the diff.
That box is just sealed with RTV, I took it off, cleaned it all up, and new RTV along with a new solenoid "while I was there", and no leaking for the past 2 years since. I think this is a more common issue than people think. They're more likely to blame the seal at the back of the transmission, which is WAY more work to "fix". I didn't touch that seal.
So just 4 bolts and it lifts off?
I need to get a mirror and look up there.
Last edited by 1999corvettels1; Jan 20, 2019 at 07:18 PM.
Based on the location in your original picture, it could be a leak between the transmission and extension housing. Very common leak for the C5. GM did not use a gasket, rather, an anaerobic sealant. After years of use, the sealant deteriorates. If you’re sure it’s tranny fluid, that’s my guess.
In order to fix properly, you’ll need to drain the transmission, drop the rear subframe and separate the 2 halves and reseal.
I just did this last month when I replaced my clutch.
Based on the location in your original picture, it could be a leak between the transmission and extension housing. Very common leak for the C5. GM did not use a gasket, rather, an anaerobic sealant. After years of use, the sealant deteriorates. If you’re sure it’s tranny fluid, that’s my guess.
In order to fix properly, you’ll need to drain the transmission, drop the rear subframe and separate the 2 halves and reseal.
I just did this last month when I replaced my clutch.
It's drained, about to get filled with new transmission fluid.
I may just save this for when I do a clutch job.
The garage floor is already stained from drips, and now spilled fluid as some bounced out of drain pan as it came out of transmission. Lol
Found a good pic of my transmission when I pulled it out..
Aside from leaky diff seals, it was pretty obvious that the reverse lockout solenoid box was leaking. I had the same looking drips on the bottom of my trans as the OP.
Honestly, if a clutch job is in the future, just wait to fix the leak then. The driveline has to come out for that job, and makes it WAY easier to fix whatever is leaking. As long as the leak isn't bad and you stay on top of the fluid level, I think you'll be fine.
I just had my driveline out to replace the clutch. I addressed all leaks including the axle seals and DS o-ring. Like DetroitPlac said, wait until clutch time and keep up with maintaining fluid levels.
T56 or differential leak
