70 Eldo Transmission Fluid Leak

[Doradokid]

I have two '70 Eldorados. Both leak lots of trans fluid when they site for a longer while.  I have had the gaskets and filter changed on one of the cars and it still leaks.  I have been told by one person that the leaks have much to do with the design of the front wheel drive axel and where it connects with the wheels.  Not sure if that is true.  Have any of you with '70 Eldorados had a similar leak issue and what did you do to stop the leaks?  Thanks for any help and advice you can offer.

[wheikkila]

My first question is how long are they sitting without being started? If it is months. It sounds like the converter is draining back into the transmission. If this is what is happing its going to be hard to correct. It is not like replacing a bad seal.
          Thanks Wayne

[savemy67]

Hello Doradokid,

Following up with Wayne's comments, if the fluid level rises in the transmission due to converter drain-back, the fluid may reach an opening/seal that it was never intended to reach when the car sits for a short period of time.  Was every seal and gasket replaced?  Can you determine where the leak/leaks originate?

Also, is the leak transmission fluid and not differential fluid?

Respectfully submitted,

Christopher Winter

[The Tassie Devil(le)]

The first thing to check is to see where the leak/s are coming from.

It is pointless trying to fix something without knowing what has to be fixed.

The only way to find a leak, is to get under there, and physically look and feel for damp patches, and then track the location of the leaking point.

If the underneath of the car is dirty, then wash it with degreaser or steam clean, and then, after it has dried, place large sheets of white paper under the car, then just watch.   When a spot appears, you are at the starting point, of the search that is.

Then, is it transmission fluid, engine oil, differential oil, brake fluid, or even windscreen washer fluid, and heaven forbid, coolant fluid.

Plus, there are lots of places where transmission fluid can escape.

Bruce.

[wrench]

My '70 drains back a bit and leaks onto drain pans, it doesn't lose a large quantity but it drips. The '69 doesn't leak as much but does drip. Again a drain Pan with pig mats solves the problem.

I have not had operational issues or significant consumption issues, so I just let them ride and just keep tabs on the fluid levels.

[TJ Hopland]

Its got nothing to do with the drive shafts.   The final drive / differential is its own unit with its own oil and its got its own seal on its input shaft and the transmission has a seal on its output shaft.

Like others have said when it sits the fluid drains out of the converter and raises the level well above the pan so things that normally don't have to deal with much fluid become a problem.   

The electrical connector has an o ring on it and the connector itself is plastic so it our the oring could be leaking.  Its the same as the THM400 so replacements can be had. 

Shift shaft is a common place for leaks.   I'm not sure if any of them had an actual seal like many of the 400's had or if they were just o rings.  All that I have tangled with have just had an o ring. 

Dipstick/fill tube has an oring and is also a great place for a leaks.

[wrench]

The 70 leaks around the Governor shaft seal when it sits, that's one leak I can see.

[Cape Cod Fleetwood]

My tranny was completely restored a few months ago, the drive shaft re-conditioned.
I still have a drip, LOL! Seems to be coming from the stupid drain plug and there's a limit to how many
times you can crank on them. BRAND NEW higher capacity pan with 'cooling fins' which might be snake
oil, super thick 100% cork gasket. Others have bigger issues. I get the aluminum cookie pans from the
dollar store and stick them under The Ark, and wipe them out when they get too icky.

Or -

"If its not leaking, its empty" - M. Amster

[The Tassie Devil(le)]

Now you know why GM didn't put drain plugs in the Automatic Transmissions.

No real need for them.

Bruce.

[James Landi]

Had the same problem when storing my 85 Eldo convertible--- I used a turkey roasting pan.  Didnot leak when I used the car regularly, but over a month's time in the garage, the fluid would drain (mysteriously)--- over a winter of storage, I collected maybe a pint- plus.  I considered the loss and inconvenience part of the "experience."   Happy day, James

[TJ Hopland]

If you need to cover a larger area and the leak isn't bad cardboard or a carpet scrap works well but you do have to change it from time to time.    For bigger leaks or longer term parking where you may need some capacity you can get large pans made for washing machines.  They are like 30x30x1 and under $30.


https://www.homedepot.com/p/Oatey-28-in-x-30-in-Plastic-Washing-Machine-Pan-with-1-in-Furnished-Drain-Adapter-34067/100080446?

[The Tassie Devil(le)]

Another thing to remember is that when these cars were new, they were being used, and not stored away for extended periods, which would be a reason why Cadillac didn't bother to be concerned about this problem.

But, the Manual does stress not to overfill.

Bruce.

[bcroe]

My tranny was completely restored a few months ago, the drive shaft re-conditioned.
I still have a drip, LOL! Seems to be coming from the stupid drain plug and there's a
limit to how many times you can crank on them. BRAND NEW higher capacity pan
with 'cooling fins' which might be snakeoil, super thick 100% cork gasket. Others
have bigger issues. I get the aluminum cookie pans from the dollar store and stick
them under The Ark, and wipe them out when they get too icky.

I think your new pan is the problem.  I put some of that blue gasket maker on
plugs and gaskets I am re using, and they do not leak. 

I do not agree, I do not want to be cleaning up messes, so a drain plug
allows me to get enough fluid out of my TH400 or TH425 pan to drop it
without any running fluid.  YESTERDAY the TH425 in my 79 Eldo was acting
up after 2 decades, I decided it was a plugged filter.  Seemed 1.5 gallons of
dirty trans fluid came out of that drain I added when I built it, would surely
been all over everything without the drain.  Today the new filter and fluid
restored the trans operation.  Bruce Roe.

[Cape Cod Fleetwood]

I think your new pan is the problem.  I put some of that blue gasket maker on
plugs and gaskets I am re using, and they do not leak. 

Its obviously the drain plug. As Bruce said these are a 'new' thing and I understand it eliminates the
mess of changing tranny fluid. Maybe some Permatex gasket sealer around the outside of the plug...

[Big Fins]

New? All of the Dual Coupling Hydra-Matics had a drain plug. I only wish the THM400/425's had them. It sure would make a fluid change a lot easier.

[TJ Hopland]

I thought the American way design wise was just let everything leak a little and as long as you keep adding it eventually gets changed on its own?   Seems like just about everything built before about 1990 works that way.