Engine Stalls Out - Suspect Torque Converter?

Hello all,
New User here, thank you for the add!

I have a 64 Buick Electra 225 w/401 & ST400

Engine starts and runs fine and actually drives fine. It's the initial launch where I have a problem. Looking for thoughts/ideas of cause.


When I shift from Park to Drive, the engine stalls out completely. It's as though the trans is bogging the car down. I say that because if I park it on downhill and start the car in Neutral and let it roll a bit, it studders but eventually takes off fine.

Also, once I'm driving but coming to a stop light, it takes all my might to hold that brake to keep the car from rolling forward.

I suspected the Torque Converter is in full lockup so started checking transmission things; detent switch adjustment, fluid. But no change. ( I have not changed the fluid, but it looks/smells ok).

Looking for ideas or what I might try next,

Thanks !

WanSolve

a ST-400 is basically a TH-400 with a switch pitch torque convertor.

therefore, for service purposes, the 1966 Chassis Manual should apply to your transmission:
https://www.teambuick.com/reference/...ssis/index.php

you're looking for page 74-156

'64 TH400's DID NOT have switch pitch converters the 1st. year.