Sudden Transmission Oil Leak 1976 Fleetwood Brougham

[dannygila]

Hello All,
I've had my 1976 Fleetwood Brougham (500ci) for a little over a year now. Whenever I take her out of the garage for a ride, I always look at the garage floor for any spots on the floor that would indicate a leak. Floor is always dry as a bone. I have not driven her in about two months since I have been slowly trying to get the AC working and do not like to drive her on hot days. Yesterday, I went in the garage and there was a river of transmission fluid on the floor, probably at least a quart coming from underneath. It was not there as recently as a few days ago. Does anybody have any ideas why it would suddenly, pretty much overnight, start leaking that much transmission fluid after not even being driven for period of time? I looked underneath the car and where the transmission pan meets the gasket looks dry, but I can see some drips hanging from whatever the part is directly in front of the transmission pan. I am really hoping it is something simple, as I always tend to expect the worse when it comes to car issues. Thank you in advance for any ideas or input.
-Dan

[Dave Shepherd]

Not to specific describing where this is, do you mean the inspection cover under the flywheel?

[bcroe]

If a car sits long enough, some of the fluid in
the torque converter may drain and grossly
overfill the pan.  This is not an operational
problem, at worst the car may hesitate the
first few seconds while the engine pumps the
fluid back into the converter.  BUT there are
a number of seals just above the top of the pan,
and if they fail, fluid rising well above them
may dump out. 

The good news is, all of these seals can be
changed without pulling the trans.  If the drive
shaft seal has failed, the cause might be a worn
sleeve bearing which can also be replaced.
good luck,
Bruce Roe

[TJ Hopland]

Let me make sure we got the timeline correct here.  You have had this car for a year and till recently had been driving it and it hasn't been leaking.   It was parked for around 2 months and has not moved.  A few days ago it was for sure 100% dry or just not obviously leaking?  And within a day or 2 span has dumped like a quart on the floor apparently from around the front of the trans pan?

Like Bruce said sitting can drain the converter which can raise the level higher than what a new or daily driven trans would usually see but for that to happen suddenly over a couple days seems a little odd.  That's why I was wondering if it could have been slowly leaking and spreading over these last couple months and the last couple days it finally flowed in the direction you noticed it? 

[dannygila]

That's probably what happened the more I think about it. I just didn't notice it until it started creeping out into view. Will start it up tomorrow, check the dipstick while idling, top off if needed and take it for a good drive and go from there. Thank you everyone for the replies. Will post my findings.
-Dan

[Dave CLC#16900]

If my '75 Coupe (with a rebuilt transmission) sat for more than a week, it would make a mess. Winter storage meant I needed to add a quart or more to top off.  The rebuilder couldn't find it, mostly because he moved it every weekend...    Took it to another trans shop and they immediately diagnosed it as a bad vacuum modulator.  Changed that and stopped leaking.  He also said my spark plugs were likely fouled from sucking trans fluid.  They were due for a change anyway...

[Cape Cod Fleetwood]

I'd check your tranny cooler lines too...
Just because a wet spot is 'here', doesn't mean the leak is 'there'.
Cars can break just being parked. And seals are a thing as mentioned previously.
When my car is driving regularly there's no rear end drip. Then moth ball it for a month... 

[Chopper1942]

The areas that only leak after sitting for an extended time are:
1. Trans fill tube o-ring
2. Speedometer gear housing
3. Transmission range shift shaft
4. Vacuum modulator o-ring
5. Electrical plug

I would suspect the fill tube o-ring first. It is very common for the trans fill tube o-ring to leak.  They get hard from age and shrink.  When the vehicle sits and is not driven daily, the fluid drains out of the converter and raises the fluid high enough in the pan to cause a puddle to form under the car. 

A simple way to determine where the leak is coming from is to get a bottle of transmission dye at a GM dealer and pour it in the fill tube. It is only a couple of ounces.  Start the engine and run it for awhile.  If it only leaks after sitting for an extended time, let it sit.  When you see fluid on the floor, raise the car and using a black light, you will see a yellow trail from the source of your leak.

[bcroe]

I was never very happy with the O ring on the
dipstick tube design.  End of the 70s they came
out with a different dipstick/tube design that
used a sort of rubber funnel.  Lots easier to
get together when mounting a trans.  I converted
all my cars to this design, bolting to the bell
housing means all BOP units should interchange,
though there might be different lengths.  The
81 368 might be the last year for these. 
Bruce Roe

[76Caddy]

This happened to me with my '55 Series 62 Sedan.  As long as I drove it every couple of weeks or so, no leaks but let it sit for a while and the garage floor looked like a murder scene.  Seals would dry out from sitting but once I drove it and the seals swelled up no problems.  Also happens with my '69 Chevy pick/up now.

Tim

[dannygila]

Update: On Monday, I put two quarts of transmission fluid in to get it up to level, so it lost two quarts while sitting for two months. Took her for about a ten mile drive and put her back in the garage with a sheet of drywall underneath for drip detection. As of this morning, not a drip. So, hopefully that is the solution: don't let her sit for too long without taking her for a ride. Thank you everyone for all the input! I was really fearing the worst. While I'm glad I know what to do now, I'm wondering: was this a design flaw or was it meant to leak transmission fluid that much if not being driven for a period of time? While it can easily be dealt with, it is kind of a disappointment that such a beautiful car will leak that much after sitting for a while. Thanks again!
-Dan
1976 Fleetwood Brougham

[Roger Zimmermann]

Before I got my '72 Coupe de Ville, I read an article about Cadillacs from that time. A person knowing those cars well told that when parked for some time, there is a loss of oil at the transmission end. I found that strange, but it's exactly what my car is doing. For one or two weeks, no drip but more than one month, there is oil on the floor where the drive shaft enter into the transmission...

[TJ Hopland]

I think someone said it earlier what is happening is the torque converter is draining down over time which is bringing the level in the case much higher than it gets normal running. 

I guess the question would be what is different now than when they were new?  Did the converters not used to drain down as fast or at all?  Or did the rest of the trans seal up better so it could deal with the higher levels?

Where is the case vent on the 400's?  Didn't some have 2 vents?

[bcroe]

I'm wondering: was this a design flaw or was it meant to leak transmission fluid that much if not being driven for a period of time?
-Dan   

The car was designed not to leak until after it
was driven off the showroom floor.  It definitely
was not designed to operate in original condition
for half a century.  Rubber parts and a few other
things need to be replaced after a couple decades,
something I have learned to do as maintenance. 
The inside of the trans may need some attention
as well, I do them after a couple dozen years,
retaining most of the expensive hard parts. 
good luck, Bruce Roe

[Cape Cod Fleetwood]

Update: On Monday, I put two quarts of transmission fluid in to get it up to level, so it lost two quarts while sitting for two months. Took her for about a ten mile drive and put her back in the garage with a sheet of drywall underneath for drip detection. As of this morning, not a drip. So, hopefully that is the solution: don't let her sit for too long without taking her for a ride. Thank you everyone for all the input! I was really fearing the worst. While I'm glad I know what to do now, I'm wondering: was this a design flaw or was it meant to leak transmission fluid that much if not being driven for a period of time? While it can easily be dealt with, it is kind of a disappointment that such a beautiful car will leak that much after sitting for a while. Thanks again!
-Dan
1976 Fleetwood Brougham

After you checked the dry wall piece did you get the engine/tranny hot and check the dipstick again?
Its just my aviation background... anything with an engine loves playing "Stump The Human".

[Chopper1942]

Guys, the transmissions did not leak by design. Heat and age cause the seals to harden.  Even when new, the torque converters will leak down when setting for an extended time without starting the engine.
Other than the front pump torque converter seal, front pump o-ring seal, and front pump bolt seals, the other seals and gaskets can be serviced in the vehicle.

As far as the leak at the rear trans seal for the front driveshaft yoke, depending on the the application of the Turbo 400, not only is there a seal in the extension housing for the outside diameter of the front yoke, there may be an 0-ring seal on the transmission output shaft.  This seals the inside of the front yoke and its splines from the fluid.

Some front yokes on Turbo 400's have a small vent hole in the front yoke cup plug to allow the yoke it more easily move on the output shaft splines.

[Roger Zimmermann]

As my '72 coupe is more and more leaking at the transmission's rear, I remove the drive shaft yesterday to see if there is a hole in the plug or if the plug is leaking. Boy, those drive shafts are heavy!
Anyway, there is a hole in the middle. Therefore, I had a look into the parts list and I found that, group 4.318, the is an O ring on the output shaft (why did I not look earlier?). In consequence, I ordered a seal and gasket for the extension.
With the drive shaft out, I'm seeing clearly that the yoke has a provision for an O ring; this was used from 1964 to 1981 on THM 400 according the the parts list.

[Chopper1942]

Good job Roger! Glad someone is reading the posts and helping solve their problems.

As for the other areas for leaks, get some trans fluid dye and install it.  If after sitting and you see some spots on the floor, raise the car and place on jack stands, get a black light, and inspect the seals I mentioned earlier. If one is leaking, you will see a yellow streak from the dye.

Dave CLC#16900:  There is an o-ring seal on the vacuum modulator, which is replaceable, that can leak, but most often the diaphragm inside leaks and the engine then sucks out the ATF and burns it.

[Roger Zimmermann]

Last Saturday, I began the work to replace the O ring at the output shaft. Four bolts from the transmission's extension could be removed without problem, but two were not reacheable. I supported the transmission with a jack and began to remove the bolts from the rear engine support. Theree nuts came out without problem (the bolt's head must be retained with a wrench). It was another matter with the fourth one! No space to insert a wrench; finally, I took a bit of steel and did a fork. Worked great! I had to push the floor to extract the bolt. If the shop manual is telling that the rear engine support can be slided backward, it's maybe without exhaust tube! Finally, I had enough space to undo both remaining bolts from the extension. I replaced the O ring, put a new gasket over the extension and reassembled. I put two thick washers between rear engine support and mounting block because the transmission was resting on the rear engine support.
Again, three bolts for the rear engine support could be inserted without too much difficulties; for the fourth one, an hydraulic jack pushing the floor (which is really flexible!) did the trick. The rest was just "routine". I have to say that the rear of the car was on jacks but not the front to avoid loosing oil. Not comfortable to work that way; maybe with 20 years less it would be a tad easier...
if the oil leak is coming back, I will do like a French guy: he just put a small screw into the plug's hole...

[Philou2]

Some front yokes on Turbo 400's have a small vent hole in the front yoke cup plug to allow the yoke it more easily move on the output shaft splines.

Roger,

French guy is here too !   

This was exactly my case and since I plugged this little hole at the bottom of the yoke it no longer leaks.
I also think that if there is a lot of oil in this place which could prevent the yoke from sliding, the oil would come out elsewhere, towards the gearbox for example which, in any case, already has ventilation via a pipe on the top of the box housing.
So in my opinion there is no internal overpressure to fear in the box due to "pumping of the yoke".