Transmission leak and ATF level
 

About month ago I found a huge puddle of transmission fluid under my car that just kept increasing. So I took my car to local mechanic who specializes in C3 Corvettes and he told me that my transmission just needs some simple service. He changed transmission fluid, filter and several bolts.
Next day I found a puddle of ATF under the car again. It was all new fluid, I know that because I have cleaned the floor and placed cardboard under the car to verify that it is not leaking any more.

It seemed like oil was leaking from front top part of transmission and dripped down over torque converter housing.

I did not have money for more expensive repairs at that moment (next step would be pulling transmission and checking seals and bolts next to torque converter), so I just continued to drive the car every day and checking ATF level regularly. And after a few days the leak just stopped! How could that happen?

ATF level now seems to be a bit high. I tried checking it in different conditions: engine running and not, cold and warm. When engine is running ATF level is on about half inch above "running max" mark on dipstick. Could it be that the mechanic put too much fluid into transmission and it was leaking through some kind of valve designed for that?

What is the correct way to check ATF level on this car?

I have 1980 California car (originally 305 engine that was swapped for 350) with original 3-speed automatic transmission (probably THM200?).

No type of check valve, but too full can leak in several places- dipstick tube, detent (or TV cable, speedo cable, shift linkage, and possibly the front/rear seals or even the vent. IF your trans has a 3rd gear switch for the TCS, they have been known to leak too.

There is a breather on top of the trans that will shoot oil if it is over full. I doubt with such a small measure on the dip stick that is the issue.

You need to get it in the air and clean it all down using carb cleaner and rags and then closely look for the leak .

To check your automatic transmission fluid...it should state it in print on your dip stick:
Transmission in PARK....Engine hot or at operating temp...idling...on LEVEL ground. That is how it is done....PERIOD!

SO if the engine is cold and not running does absolutely nothing.

DUB

UNLESS you compare and mark readings under BOTH conditions.....

:thumbs:

Dub is nuts on .. That is how you do it .. It is not debatable lmao ..........

I'll add you also need to look at BOTH sides of the dipstick. I've sure seen a bunch that were at the full mark on one side any way over or under on the other side. The correct level will be even on both sides. It must be the angle the stick gets into the fluid.

I just looked at my owner's manual and it says the car must be driven for several miles making frequent stops and starts to bring the transmission up to normal operating temperature (180-190 degrees).

Idling in the driveway isn't going to get you there.

Well guys his real issue is a leak .. He was worried it was over full causing a leak and my money is on NO .. Lift it . clean it , check it. Then check fluid level after needed repairs are made.

:iagree...but I have had several customers over the years who actually pull there transmission dipstick when the car is just sitting there (not at the correct temp and on un-level ground also) and look at it like it is going to tell them something...which is incorrect.

That is why I replied the way I did previously...because some people just do not know.

DUB

Thanks, guys!

I was checking ATF level incorrectly (on uneven surface), will try again according to your instructions.

Here is where my TH350 leaks from.
TH350 Leak

This left a 3" spot on the floor everyday without the car running. Just sitting. At first I thought the pan gasket was leaking, after 2 attempts at the pan gasket I stuffed a rag up between the torque converter and the tranny. Next day no drops on the floor, but the rag was nice and red. After removing the tranny I could see where the leak was from. Replaced the front pump seal's and now all is dry again.

If all your seals are good over filling will not cause a leak. When I had my unit out I filled it with extra fluid to make sure nothing leaked before I put in back in. Let it sit for 2 days. 1 day leaning forward 2nd day leaning backwards. Nice and dry. removed fluid before installing in the car. Then filled to level cold. Ran the car and filled as required during warmup.

Your one of the few to get away with just a seal replacement , the front pump seal almost always leaks because the bushing is bad that the T/c rides on.

I am sure that will be the next source of leaks as this is the original TH350 with 110k Miles. Never been rebuilt only serviced every 35k. Need to keep it running until I figure out what the next transmission will be. Waiting to see what or when Richmond Transmissions will return to production. The TKO line doesn't have what I want. looking for 6 speed with 1 overdrive or 5 speed with no overdrive.