Active oil leak at the back of the engine. Visible at the right-rear, above the oil pan joint. Just replaced both oil pan gaskets, figuring how to get around the leaf-spring tensioner to drop the sub-frame.
The leak is still there. Searched IATN archives, no hits. Replacing the rear-main oil seal is a massive 10 hour job. Is there another possibility?
I don't work on a lot of Corvettes, but am old-school, and fix whatever is in front of me, even if it becomes a "learning" (read: giving) process.
There are a lot of posts about oil pressure sender leaks. A couple of years ago, earlier generation Corvette, I replaced one. Pulled intake manifold, etc. Is this the same? Common? Mounted at the back of the valley?
I liked that picture-post of machining a fitting to mount the sender remotely on top of the engine!
Andy Grabiec <pailnm@comcast.net>

 

Yes, it is fairly common for the oil pressure sender to leak and yes the leak would appear at the back of the engine. You should look at that. As far as the rear engine seal leaking, it does not appear to be a very common problem according to the posts that I have read. They are not prone to leaking. However, that doesn't mean that it's not leaking in your case.

There is also another thing that you can look at. I see that you changed both oil pan gaskets. Did you use the proper torqueing sequence and a proper torque of 106 lbs/in? Just something to look at.

 

Thanks, Cybermind, for your input about the prevalence of leaking oil pressure senders. But, the easy fix was not to be.
Friday AM I pulled the intake (not too difficult) and found the O.P.S. totally DRY!! Well, the intake o-rings were shot anyway.
There is a rubber cover at the bottom of the, well where the torque converter would normally be located, behind the engine. I never thought to look there. Too obvious, I guess. The rear main seal is visibly wet. The oil is NOT dripping down from above.
So, on Monday I will disassemble and revel in being an experienced Corvette mechanic. First, though, I'll reassemble the intake and run the engine to watch it leak.
Thank you again for your response.

 

Sorry to hear it's going to be a bigger job,,,,good luck on the fix!!

 

Good luck with repairs

 

I had a 1980 Pontiac Turbo Trans-Am and I too had the impervious rear main oil seal leak. They used a rope seal back then but hopefully its a better seal now for the corvette. The sad part about it is that it will continue to leak until repaired. Not a pretty picture any way you look at it. Good luck with the repair. Let us know how you make out.

 

Good luck with the repair

Chuck

 

I have the same oil leak on my '99 A4 w/35K miles. If I wipe the area, the drip reappears a few days later whether the engine runs or not. It seems to come from the hole at the bottom of the bell housing. Dealer told me leaking rear mains on these cars are not common but always possible. Any thoughts?

 

I've looked at the underbelly of the Beast, and think, barring practical obstructions, that I can drop the entire rear suspension, along with the transmission+differential, axles, and torque tube as one piece. Wiring and hydraulic lines are a given. What technique I used for the front cradle should also work for the rear cradle. Years ago, I built an adjustable dolly to remove drivetrains. This should work now, too. (No patents)
Maybe I'm an "idiot savant", but I like to surmount challenges. It is really fun, in a way. I will keep the Forum posted, as I am astounded by the interest in my "Corvette Experience".

 

 

Good luck with the repairs

Take some pic's along the way...

Nick

 

To your last point, I think some folks are intrigued with your tenacity.

 

I have found the leak source! Yes, I removed the Rear Suspension with Transmission+Differential and Torque Tube as a unit. The only thing that I didn't anticipate was the brake lines curling around the differential, under the half-shafts, to the flex hoses w/calipers. So, bleed it.
So, I zap the bolts out of the rear-main carrier. It comes out easily. The gasket is flat. Silicone bonded rubber to aluminum. It would have leaked soon anyway (or maybe it was contributing). The REAL LEAK is the CAM POSITION SENSOR O-RING just above the rear main retainer.
Now, remember your "old-time" 350 (OK:5.7l) Chevy. The distributer fit into a hole in the block. It had a gasket. This is an aluminum cast block. It doesn't have a distributer, but does have a cam sensor. And, the block is differently designed. Remember that I said that from the upside that everything appeared DRY. Yes. From down below, with the housings removed, the cam-position sensor was visible. BUT! BUT! there is a space between where the CMP bolts down, a "dry-space", and where it seals in the aluminum block, about 1 1/4 " lower!
This was never part of older 5.7 liter cast iron block engines.
The O-ring is only available with the Cam Sensor from GM. OK, it could be cracked, also. This is soaked with oil. I had the GM come out and stick his finger in the oil (oh!).
The oil drained down over the rear main carrier on both sides. Four PM on Tuesday. I will keep all of you apprised.
But, could I have found this leak-source without disassembly? Only if someone had worked on Corvettes for years. I only have 38 years in the trade and the normal upper level certifications. Crystal Ball broken.

 

Wow. I never knew that those sensors could leak. Please keep the updates coming. I always look forward to your next post.

 

One of the mobile tool dealers mentioned, when I told him of my findings, that the nearby Chevy Dealership does a lot of rear main leak repairs.
Hmmm. Maybe they know and are making a buck. Dealerships are like that---a war zone. I was never inclined to stretch the truth, but that's a judgement call. This is the grey-area of auto repair, as in most professions.
Posted in Mechanical & Parts, C5, if it doesn't connect automatically. It is not the only thing that I have worked on this week, and I'll finish it tomorrow, If I haven't built-in the monkey wrench!

 

Rainy Friday afternoon (rare in New Mexico) and I had the time to finally assemble the remaining intake manifold. I brought a shop-vac from home to clear the sand and mouse **** to make a cleaner job. That 5/32" vacuum hose in the back, which you can't reach, I extend with a one foot length of hose with little zip-ties preventing dislodgement.
I ran the 'Vette on the lift for a half hour before the road test. No leaks visible. Did 20 miles in the rain (no fun). Examined the joints on the back of the block again.
Not a "leak", really, but visible "sweating". It'll be a dirt-catcher, but not a dripper. All GM gaskets installed clean and dry, except for joints which got a dab of viscous silicone sealer.
Until this moment, I never thought of holding a straight-edge across any parts. Possibly, there is some warpage. Now, I don't know.
In the future, I would be tending to R&R the engine, rather than pull the trans/diff & rear suspension. I haven't looked at labor times to compare.
So, tentatively, I will call this repair a success.
The REAL OIL LEAK was the Cam Position Sensor o-ring, in a space just above the plate that holds the rear-main oil seal. The o-ring isn't at the top, but about 1 1/2" below. The sensor is particularly long. The camshaft constantly throws oil at the sensor. The little cavity fills up, then runs down the back of the engine. This is inside the bell-housing, behind the flex-plate.
See you later. Andy

 

Without further review, the CPS O-ring could very well be my problem on the '99. What's a guy lookin' at for time to patch it up?

 

Once the plastic intake manifold is removed, the cam position sensor is next to the notorious oil pressure sender. It is held in place by one bolt, and there is no indexing or calibration, since it just senses a passing protrusion on the spinning camshaft. It has 3 wires, therefore it is a Hall-Effect sensor, not an AC reluctor type.
In my case, the sensor wasn't really bad, just the o-ring, which was unavailable separately. ACDelco part retailed at $90.00. Don't buy cheap. Maybe they are all made in Mexico, but I highly recommend OEM parts.
Further, just a correctness point: In OBDII jargon a Camshaft Position Sensor is abbreviated as "CMP". A Crankshaft Position Sensor is "CPS". The CPS tells the PCM rpm and monitors misfires. The CMP indicates where the engine is in the 720 degree cycle of the engine.

 

I agree, buying on the cheap here is just making a future date with the same repair. $90!!! Damn Corvette tax again.

 

Perversely, this job was "fun". Without investigation, exploration and knowledge, such a quest might result in throwing wrenches. But, I'm not like that. Made by people and can be fixed by people. As I often say, "If GM made them any better, I wouldn't have a job."