72 Transmission information

[saddletramp]

Hi Guys i need alittle help my 72 C,20 has a Turbo Hydra -Matic this truck had a manual transmission in it the PO swapped to the Automatic i dont no much alse about it i hoping to get some answers while driving it it shifts almost to 20mp then between 30 mp after that i dont feel or hear it shifting again when should it shift again ? does it shift when it you get,s up to highway speeds with more vacuum and i was told its a very sought after transmission can some one explain this transmission for me much appreciated. Saddletramp

[Bigdav160]

TH400

It's a three speed so it shifts twice

[saddletramp]

Thank you for the Help

[Steeveedee]

FWIW, millions of these were produced. Some are more sought after than others. There is a tag with a code on it. If you want, you can see what the code you have tells you about that transmission. There's a list somewhere, but a brief search turned up nothing for me. Maybe someone else can chime in with that link. I used to have it, seem to have lost it.