th400 pressure problem

[DetroitDan]

Need some help fast. Only driven this truck twice now, prior to driving it I noticed the t-case was way overfull, and remembered the p.o. saying he had to add fluid. So pulled t-case off and replaced the seal between, seems the tranny was pumping fluid right into the t-case. Don't know if it was pumping in because the seal was bad, or if the seal was bad because the pressure was too high.
So I drove it today, it felt a little wierd taking off through 1st gear when it was cold, like it was slipping maybe, but then it worked out and was driving and shifting great. At about the 4 mile mark I saw a huge cloud of smoke blow out the back and said well I blew it up. Smoke cleared immediately, continued to run and drive fine, so I figured some trans fluid hit the exhaust and burned off. Only had a mile to go so I continued on with no problem. After parking and shutting it off I noticed a minute later some smoke coming from under the passenger front side, looked and saw trans fluid on the starter and that general area. No leaks that I could see, eventually opened the hood to look and realized the whole dipstick tube was wet, it seems like it "burped" out of the tube, got on the exhaust and burned off.

What would cause the pressure to be too high, and how do I fix it? I haven't owned a non-electronic transmission in afew years, so I'm trying to remember what a modulator valve acts like when it goes. Maybe a clogged cooler line? Or a vent or something? Shouldn't be overfull but I guess maybe it could be, need to heat it up again to check the level. Little leery of getting it hot, don't want a fire from the fluid hitting the exhaust, also don't want to blow the trans seal again, if I already haven't.

Please tell me this is a simple fix that isn't going to involve pulling the transmission.

Thank you

Oh yeah, it's an 82 454/th400/np205

[DetroitDan]

well the trans and t-case are pretty dirty, there is a lot of crud in that area because the t-case vent was working and spewing the overfill coming out of the trans. So all the dust and dirt stuck in it and caked on. The truck was mostly driven on dirt roads, so it is mostly spotless except where there was some leakage, and that's all caked-on crud. So I got my fingertips on the vent hose and all I could do was snap it against the bellhousing a few times, hopefully enough to free up any junk in it.
Trans turned out to not be overfull. Lot of places I found online said the th400 will spit out any fluid that you overfill. I ended up getting it warmed up and finding nothing on the stick, had to put 4 1/2 quarts in it. Here's what I think happened: when we changed the seal after the tranny pumped it's fluid into the t-case, I didn't realize it had pumped out the torque converter too. So I filled the pan up with 7 qts, but after running it and moving it around a little it got drawn into the converter, leaving the pan low. I don't know if a low condition could cause pressure, or a plugged vent is still at fault, but I rattled the vent and topped pan off and it is working, Also possible the dipstick wasn't seated in the tube. Drove it a few miles with no problems, no burping, spewing smoke or slipping,

I checked the t-case, it was not overfull so it seems like the seal stayed intact. In fact, there was nothing in it. Apparently after we put it back up some nitwit forgot to refill it. It's not leaking. Really lucky I didn't drive it much, and this spurt actually saved me by making me look into it. It was last winter when I worked on it last, so it sat for many months and I'd forgetten what else we had left undone I guess. With a half empty tranny and an empty t-case, I would have done some serious damage once I put it on the road. But all I did was move it to the new house, it will probably sit there for the winter.

Once again my poor memory and attention span almost bit me. Oh well, I guess I'd rather be lucky than good!