My TH400 that I got rebuilt a little over a year ago is leaking over a quart of trans fluid everytime I top it off and park it at an angle in my driveway. It doesnt leak right away but after a day or two it will leave a huge puddle. It is wet on the around the ujoint and I noticed a drop on the ujoint itself but the rear seal seems dry. I am thinking the convertor is draining back and causing it to overflow. Ive changed out the speedo housing, tightened the pan, and a bit confused on what to do next as I am tired of filling it up and staining my driveway.

Any ideas?

 

Make sure you check the transmission fluid with the transmission hot, idling in park on a flat surface. Then top off the transmission.

Have you contacted the shop that rebuilt it? There's no reason a transmission should loose that much fluid with a recent rebuild.

 

Try to identify source/location of leak. Add a little fluorescent dye to the ATF, take for a ride then visualize w/ a (UV) black light. Most automotive parts/supplies stores sell both the dye & a small pen light flashlight. A small 30mL bottle is ~$8.00 - $9.00. Ensure it's dark outdoors/indoors when visualizing with a UV light source. Tell-tale traces of dye will show up at the leak source.

 

I have checked it while hot on level ground and it is below the dip stick before I top off. It also will barely move when it's that low until I top it off. I haven't contacted them yet.

 

I bought and added some of the UV die last week but it drained so much ATF that it didn't help.

 

You can see a drop on the UJoint and the wet area on the under carriage where the ATF is flinging to

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Do you have an original "fill" tube and dipstick ? How long has this been happening ? Has it been leaking since you put the transmission in ?

First, warm up the transmission by driving it and check the ATF level on flat ground per the CSM.

Second, try to determine where the transmission is leaking.
You can place a piece of cardboard under the transmission and check for drops every few minutes. This should help you generalize where the leak is.

Third, if you determine the leak is from the rear seal area.
Tape an opened one quart Ziploc bag on the transmission housing spanning the rear seal area, taping the other side to the yoke.
This should help you isolate a rear transmission leak. If the leak is on the outside of the yoke, you may need to install a new seal.
Tape an opened one quart Ziploc bag on the yoke (in front of the U joint) and to the driveshaft.
This could help isolate a rear transmission leak coming through the inside of the yoke. If the leak is coming from inside the yoke, you have a bad, missing or wrong size "O ring" on the output shaft OR you have the wrong length drive shaft, possibly the wrong yoke.

 

I don't have the original fill tube this was supplied by the transmission shop when they installed the TH400. Driveshaft was custom made to fit the TH400 as my original was for the 2 speed Jetaway.

It only started leaking after I stopped driving it regularly a few months ago but seems to have gotten worse. When it drains it gets so low the car will barely move. I posted a photo of the only visible area that has a leak/drop. I can try to do the ziplock suggestion and see what happens.

I've seen some threads where people had a leaking from the weep hole on the yoke?

 

A couple suspect areas to evaluate: (1) speedometer cable connection seal; (2) transmission modulator valve [O-Ring]; (3) transmission rubber cooler lines; (4) shift shaft linkage seal.

 

When I started to reply, there was no pics and no one replied. And it appears some people with shorter replies posted first. I just saw the pic of the yoke.

Since it started leaking, then I would think its a rear seal or Output shaft "O ring". With the Ziploc bag, its cheap and you can see how much is draining. It might be time to have the transmission shop look at it.
If the driveshaft is too short, leakage will come from inside the yoke and out a "weep hole". .