01 F-150 7700 ed.

I have a 4R100 Tranny with a 139K miles. It has been rebuilt. Ever since the rebuild (over 10 yrs ago), if I park the truck for a week or so or more, I will end up with a decent size puddle of trans fluid underneath the truck. I took it back to the shop that did the rebuild a couple times, but they could never find anything. It leaks enough to where my fluid level drops enough to cause the transmission to slip in a U-turn because the pickup tube becomes uncovered. I have a couple theories, but am wanting to hear from the collective.

Theory #1 When I park it on my slightly sloped driveway I don't regularly use the parking brake, so it rests on the gears, which eventually forces fluid out an overflow or breather tube.

Theory #2 (a very thin one) due to pressure changes associated with the weather, fluid is somehow siphoned out a breather tube due to some blockage internally in the tranny to where it's not equalizing with the outside air and has a high pressure within... ( i kinda laugh at myself for this one, but I am at a loss over the source of this)

I have nothing else... Any ideas? Thanks in advance.

 

With that much leakage, it shouldn't be too hard to find WHERE it is leaking from. I'd start there.

 

My theory is that the torque converter drain back valve isn't sealing very well. When it sits a long time the torque converter drains into the pan, which raises the fluid level. This valve is in the pump body, so the trans has to come out to inspect it.

 

I would also tend to think that the location of the leak will tell the tale.
Find the wet spot.

 

Check the case connector we had one leaking though the connector

 

Thanks for the replies.

I did go staring up there a few times post puddle, and it appeared to be coming from the top near the mating flange if I recall correctly, which is why I left off because I couldn't see well up there, but I'll use a better inspection mirror or camera this time. I will go inspect some more and see where I end up. Thanks again.

 

So I came home this morning and lo and behold I had a nice puddle (it's been sitting for a week or just over). I only had time today to snap these 2 pictures before I hit the road again for work. I'm going to have to jack the truck to get under there properly to get a better look, but you can see some of the extent of the issue.

 

Had a Dodge 2500 that the dipstick "O" ring failed. The dipstick just pushed into a portion of the transmission case and into the pan. It was a snug fit, and when the O ring failed, the fluid came out.

It was the same situation you describe, park it for a few days, and I had a nice puddle underneath it. And as Mr. Kovalsky mentions, the drainback valve leaking back, would cause the level to rise, and if the trans dipstick O ring is brittle, you get a puddle. Jsut something to check, the O ring is a cheap easy fix. The drainback valve is sounds like a major deal to pull the transmission.