Ok first off.............I'm having a lot of weird problems with the used $70 TH350 I put into my firebird. When I first drove the car after the swap, I noticed in 1st gear the pump buzzed a little bit. Also, the car shifted REALLY soft, but I had a 3,200 stall 10 inch converter in it, so I figured it was normal. Installed a shift kit and B&M vacuum modulater, and the tranny shifts nice and hard when you get on it. Now fast forward to the present...............been trying to run my car at the track and get a full decent pass, and it seems like in 3rd gear the tranny is soaking up the engine power and my MPH is suffering big time. in the 1/8th mile I will pull almost 90mph usually, but this last time I went to the track, my 1/4 mile mph was only 105!!!! wtf??? Whenever I hit third gear it just kinda stays at the same rpm for the rest of the run (around 5,000rpms) I'm blaming the transmission because of this.........after the run, I got on the brakes, slowed down, and went to put the tranny back into 1st gear to keep the revs up a little bit. When I did that (at about 5 mph or less) the engine seems like it LOCKED UP with the tranny, like even if I stepped on the gas to keep the engine running, the pedal didn't do anything, the engine was locked in sync with the tranny, so I stuck it back into 2nd gear and drove back into the pits. After I started the car up and stuck it back in 1st, it seemed like everything was normal. So I pulled the car back into the staging lanes and tried to make another run. After heating up the slicks for about 10 seconds in 1st and 2nd gear, I inch up to the starting line and slap it down into 1st................and BAM, clunks down like the motor is locked to the tranny again!!!! WTF??!?!??!?!?!?!? It only does this every once in a while, and ONLY when I'm at the track on slicks, not on street tires, because on street tires it will just spin. Any theories here?????? WHy does my tranny "lock up" in 1st gear sometimes?? Its a 3,200 stall 10inch converter so putting the transmission in 1st gear from a stop should not lug it down to a stall.

 

Sounds like you have a leak inside there somewhere that's applying an extra clutch part of the time; shifting it into 2 gears at the same time in other words. Sounds like the intermediate clutch is the thing that's staying partly applied.

The trans is not long for the world with that going on. Something is constantly slipping in there, which will cause it to wear out rapidly.

Probably time for a tear-down and rebuild. It may even have a porblem with the case or the valve body. I have no idea, other than a visual inspection, how you could find that.