Thread: TH400 Troubles

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Hey All,
I have a 76 chevy truck with a 454 and a TH400 tranny. I drive it all the time and am now starting to have tranny troubles. The trans doesn't want to shift out of gear unless i put the pedal to the carpet. And when i do that it shifts really really hard. From a dead stop and then going i don't even think i get first gear. I think it goes straight into second and stays there unless i pound the throttle, like i said before. I know i still have a working first gear because i can still manually select first and i can feel it shift into gear. Same goes with second. I can manually select the gear and i feel it in that gear. That is basically what i know. I have limited knowledge of transmissions, especially automatics so any help diagnosing this problem would be greatly appreciated.

Thanks a lot
-Tyler24

Pull the pan and see if you still have the old style kick down solenoid. It's a can looking solenoid. The older ones have a tendency to stick wide open causing the problem you described. The newer style solenoids are quite different looking and have been trouble free. It is also probable that your modulator shuttle valve is hanging from debris and it always pays to take that out and clean the bore. Also changing the vacuum modulator at that time. I've posted a pic that shows what the newer style solenoid looks like.

Thanks for the response. I will try to pull the pan tomorrow if i get some time and look for what you described.

I got underneath the truck today and found out that the vacuum modulator hose was off so there was where my problem was. I figured i would just replace the thing while i had the truck up and since debris probably got in it. So the whole job cost me 16 bucks and everything works great now. Thanks for the help.