Transmission will NOT stop leaking.

[knewblewkorvett]

I have a near mint condition 1997 Expedition XLT 5.4L with just over 100K miles.
Here is my issue, my transmission pan will NOT stop leaking. I just came in from the garage and sure enough, there is a quart of transmission fluid on the garage's floor. This is either the fourth or fifth time in the past year it's done this. I'm getting so frustrated and I'm sure my mechanic is too as he is eating the costs as he carries a 1 year warranty on his work. Here is what happens. He'll replace the pan gasket and not a drop to be seen anywhere. I'll get it home (about a 40 mile trip) and she will still be bone dry. I don't drive the Expedition much, if any, as it's the summer and I daily drive my Corvette. But, I go by my Expedition in my garage several times a day when I take my dog outside. I made a habit of looking at the garage floor because of all the instances of leaking I've had. Well, damnit, I again have a quart of transmission fluid under the Expedition again. Yesterday, not a drop. Today, a quart. She hasn't been driven since the last maintenance which included not only a new gasket but also a new pan. The 3 or 4 times before that just the pan gasket was replaced along with many bolt holes being heli-coiled. Here is another interesting tidbit. After purging about a quart of oil over night, she will barely leak. Also, after driving the Expedition 40 miles to my mechanic she won't leak a drop. WTF? I can't keep expecting my mechanic to eat the costs of the repairs and I'm tired of cleaning my garage floor. What could possibly be going wrong. In my limited knowledge, I'm thinking something is building up pressure over a week or two just sitting there until the gasket lets go. It also did this in the winter too so the summer heat theory is out and also when the Expedition is driven it will cease to leak. It also doesn't get too hot, or too cold, in the insulated garage. I'm at a loss. Is there something that is supposed to relieve pressure in the transmission?
Any help would be appreciated.
Jay

 

[riderboy1961]

Are you sure it is coming from the transmission Pan? (that doesnt sound right to me)

Im wondering if it is getting Overfilled which May cause this problem.

Have you checked the front of the transmission area to see if it may be seeping out the Front Seal and not from the Pan?

 

[knewblewkorvett]

Thanks for your quick response.
I'm 100% sure it's transmission fluid on the ground.
I have no idea if they are refilling it over max but they are my trusted mechanics. I've been using them on all 6 of my vehicles for a decade or so.
Also, if it was overfilled, how would that cause the fluid to leak week or weeks after the transmission was filled? My Expedition has just been sitting there for a week or two without a drop then, bam, a quart on the floor overnight.
I have not check the front seal but I would guess my mechanic has as all these repairs are on his dime.

 

[riderboy1961]

Can you slide under your vehicle, with a light, and see if you can find where the leak/seep is coming from.
Take pictures with Flash and add them on here, might help.
* I can only Guess when not seeing the issue Live. You stated you thought your Trnas Pan was leaking but only periodically? I dont think it is the Trans. "Pan" that is leaking, though anything is possible.
Take some pics (w/ Flash) and add them here, it will help folkes who have experience, to better help you.
(unless someone that has access to your garage is pouring trans fluid on the ground, every so often just to keep you in fear/confusion... LOL)

 

[knewblewkorvett]

Here are some from the previous leak. I can go out and take some of the current leak if you need them.

 

[riderboy1961]

in the first picture, it looks like it "could" be coming from the Rear of the transmission (if that Silver colored Pan in the picture is the Trans Pan)
Yes... please take pictures with Flash and also, slide under there (slide in from the driver side though) and take a few from where it looks like it is leaking from.
Also... Take a couple pics (use flash) of the right side of the transmission, try to include the two Transmission Lines that run out of the transmission, as well.

 

[Jim Brown]

Check for torque converter drain back and an external leak not the transmission oil pan.

 

[Jim Brown]

Maybe two problems, an internal leak known as torque converter drain back

and an external leak not the oil pan.

Note you may not have excessive torque converter drain back, however, it is draining back and the fluid level is rising over multi-day's time to reach an external leak, not the trans oil pan, which you must now find.

If the transmission takes a bit to engage after being started first time after sitting, that's a sign of drain back, as the tc is refilling during the first moments after starting. Also, it wouldn't leak after being driven back to the mechanic since the tc would be refilled, and the fluid level would then be low by the amount leaked on your garage floor.

Copied and pasted torque converter drain back test from another forum discussing a '99 Ford truck with 4R100 transmission. See below.

Torque Converter Drainback Test

Drive the vehicle for 30-60 minutes to attain normal operating temperature.
Check the transmission fluid level. Add fluid only if required.
Drive the vehicle through 8 to 10 cycles of 1/2 throttle, 1-2 upshifts to elevate the transmission temperature. Then proceed as follows:
Park the vehicle on level ground.
Allow the vehicle to sit for 30-60 minutes.
Check and note the fluid level on the fluid level indicator (7A020) with the engine off, in PARK. The following example shows the fluid level after 45 minutes.

Allow the vehicle to sit for a minimum of 24 hours. Check and note the fluid level.
If the fluid has risen 25.4 mm (1 in) or more above the level in the first check, excessive converter drainback has occurred.

If excessive drainback has occurred:

stuck open check ball in rear cooler line case fitting.
no check ball in rear cooler line case fitting.
incorrect case cooler line case fitting (without check ball) installed.
Repair as required and recheck.

 

[riderboy1961]

I like the Check Ball idea. This would possibly make some sense.

So... as the fluid slowly drains back into the pan, the pan becomes a little overfilled, though it still should Not Leak.

"As that fluid ever so slowly rises during leak back from the check ball issue, the fluid is rising up to the level where Something Else is not connected Correctly or is Loose".

I am thinking,,, Transmission Lines into the transmission case, one is Loose, or Cross threaded and not sealing correctly, or possibly the lower trans line, if there is a rubber fluid line connected to the aluminum trans fluid tube coming out of the trans case, That rubber hose to aluminum trans line Connection, may be seeping/leaking.

You Mechanic ought to be able to figure it out pretty quickly and fix it.

(Your mechanic must not have very much experience as a mechanic. When I had mechanics work on my vehicles when I was younger and the vehicle never stayed fixed... I finally realized I could fix my vehicles and motorcycles myself, correctly the first time, with 1/10 the parts and labor fees. Sorry, felt the need to say that).

*It has got to be a simple fix once you find where it is leaking from.

 

[knewblewkorvett]

Doh!
It seems it has leaked a little more since I last looked as there is quite the puddle. I took a couple of more pictures with flash on.