TH400 lack of pressure, wont go.

[70fireturd]

I finally got all the loose ends on my 1970 firebird finished(so I thought), so it was time for the first drive around the neighborhood. I drove it around for about 45 minutes and everything was going well, it was shifting fine. Then all of a sudden it was like the pressure went away and it wouldn't drive. I got out checked the fluid while it was running in park and was hot, It was completely full. So I shut the car off and was trying to figure it out what was going on. After twenty minutes I cranked it back up and I was able to drive about 60 yrds and the pressure went out again. So i let it sit and again was able to drive about 60 yrds. I have been reading trying to see if anyone has had similar problems. So far I have read that air could be getting into the pickup, clogged filter, burned up pump,or not enough fluid. I am completely confused please help.

[greycamaro]

without a line pressure reading. I would have to guess a clogged filter and/or filter dropped down? drop the pan and have a look.

[70fireturd]

I have heard the seals could be hard and not allowing it to pressurizer. I used a th350 dipstick and now I have been told that there is a 2'' difference in length. Has anyone heard that? I wonder if my fluid is low. I am trying to go through everything before pulling the pan and draining it. When I first cranked it up the mod valve blew and I pretty much threw away $60 in fluid. I was getting some gear wine out of the pump like there isn't enough fluid.