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Discussion Starter #1
C4 in a '67 Coupe. Took it in to a tranny shop a few months ago to replace the linkage seals due to minor leakage. All was well for a few days but then after the car sat unused for 4 or 5 days there was a large puddle of fluid on the garage floor. Since then, if I drive it at least every day or two all is well but if it sits for a few days I get another puddle underneath. The leak seems to be from the area of the extension housing gasket.
I have had the car for at least 20 years and it only started doing this after I had the linkage seals replaced. Is it possible that they forgot to replace something? A friend told me that there is a flow-back valve (?) that is easy to miss when re-installing the valve body.
Will replacing the extension housing gasket solve the leak?
Of course, the tranny shop denies that they could have caused this.
Thanks for any advice.
 

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Leaks can be tricky to diagnose since ATF "runs" everywhere and can make something "look like" it's leaking when it's not.
Esp if the leak is from higher up, and then it "runs down" and makes something else look like it's leaking.

First step, get some brake clean and spray off everywhere you can see ATF.
May take several applications to get the trans really dry on the outside.

Next is optional, esp for a nice restored car, but in my trans shop we get some silver paint that drys really quick,
and paint all suspected leak areas.
The silver paint makes it very easy to spot the actual leak point, since the ATF shows up very obviously on the silver.

After cleaning go for a short drive and then get it up on stands and go under with a strong light and see if you can spot the leak.
If not, let it sit on the stands and check every hour or 2, or over night if that's what it takes.

It sounds like yours leaks after sitting, which indicates that the fluid level rises after it sits.
That is because the torque converter "drains back" and raises the fluid level in the pan.

Your friend is "sorta right" about the drain back valve,
except the drain back valve is inside the trans stator (all C4's) and it can't fall out from removing the VB.

1970 and later, there is another valve that can fall out and get lost from removing the filter when doing a service,
But that valve is not a drain back valve, and is only found on 1970 and up C4's.

On those 1970 and up units, if the valve is not put back, the trans has shifting issues and shifts too early, not drain back issues.

As far as the extension housing gasket leaking (if that's the case) it is possibly a coincidence that it started leaking now.
Not defending the shop, they still might have done something.
Are you sure it's not the rear of the pan leaking and just looks like the extension housing gasket?

In my experience the rear of the C4 pan can be troublesome to seal.
Usually the center bolt at the rear likes to leak.
We used to cure it with a bit of silicone on the threads of that bolt.

Let us know what you find.
 

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Discussion Starter #3
Thanks for the response. The pan is new and I'm quite sure the leak is not there. As I mentioned the car is a '67 and I think the transmission is original. I did something similar to the silver paint thing. I cleaned the surfaces and then generously sprayed white athletes foot powder all over. The only area that I could detect fluid was in the housing gasket area. As a matter of fact, I had the car up on ramps so I crawled underneath, cleaned the area well, dammed off the area around the housing gasket with rags and waited. Before long a red bead of fluid started to show along the gasket. It just seemed too coincidental that this issue began after it was worked on. I have a new extension housing gasket and seal so when the rain stops I'll try to install that. It appears that it will be a relatively easy thing to get at the gasket. Are there any issues I should be aware of before get in over my head? Thank you again.
 

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Pretty straight forward job to change the extension housing gasket, just a nuts and bolts kinda thing.

Coincidences happen... I can't imagine what the shop could have done to cause the extension housing gasket to leak.

Gaskets do get brittle over time with all the heat/cool cycles.

Same with rubber seals, hence your linkage seals that were leaking.

If the trans has not been worked on before, or for some long time, you might just expect other seals to eventually start leaking as well.
 

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Make sure when extension housing is off that it is flat . I find run a large file over the face lightly most are not flat
 
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