TH400 question

I have a 67 TH400. Just looking for some clarification.. To my understanding the TH400 shifts by the vacuum solenoid that goes from the side of the tranny and up to the intake manifold. So Ive attached a picture and was wondering what the wiring harness That attaches to the throttle bracket below the throttle linkage?

Does this work in conjunction with the vacuum solenoid for the kickdown of the transmission?

 

On the ‘68 and up 400, the vacuum line controls upshifts at part throttle. The solenoid forces downshifts when mashing the pedal. In ‘67, you have a second connection for the ‘switch pitch’ converter.

http://www.v8buick.com/index.php?threads/67-riviera-switch-pitch-is-it-adjustable.312939/

Patrick

 

Correct that is the actuator for the variable pitch converter.....basicly a low stall for daily driving and I high stall when power is really needed

 

So how do it fully function? Is it all electronic to change the stall? Where does it get its signal ?

 

The switch pitch is normally low stall and 12v will kick it to high stall. You also have a detent/downshift switch for passing gear, also 12V. I'm not sure if it is on the inside at the gas pedal same as the 70-72 cars that were not switch pitch.

I'm not sure of the operation of the switch pitch with the factory as the one I had was via brake pedal and with a manual switch on the shifter. It would high stall at a stop light and any time I pushed the button.

 

Hi Ryan, guessing that's your first name!

The variable pitch torque converter (some call it "switch pitch") and detent function (kickdown, passing gear, what have you) are controlled by two separate electric solenoids inside the transmission which are normally closed when not energized by +12v. The whole electric side is part of the engine wiring harness. The solenoids are +12v activated electric valves that allow the flow of trans fluid when energized.

For detent, the switch beside the carburetor energizes the detent solenoid inside the transmission. If engine and road speed allow, that should result in the trans downshifting to a lower gear to help acceleration.

The variable pitch torque converter has two switches. Near wide open throttle, that same plunger switch next to the carb also energizes the variable pitch solenoid. This allows trans fluid to push the torque converter stator to a less efficient setting, allowing more slippage, and more engine rpm for quicker acceleration.

There's another variable pitch electric switch, this one is behind the carb and part of the accelerator linkage near the firewall. Whenever throttle is closed, the high stall is activated. This is nice because it smooths out idle at a stop sign and prevents the car from "creeping" forward too much. That is this switch's only function, +12v when throttle is closed.

Attached is an illustration from the '67 chassis manual showing all the different parts.

Hope that helps,

Devon

 

Thank you for the detailed explanation! Appreciate that!

 

The kickdown function is independant of the SWitch Pitch function. Both
work directly from throttle position. So the SWP function is only used at
idle (to avoid creeping) and near full throttle. I use torque sensing (manifold
vacuum) and timers to use the SWP in mid range, to make the car smoother
and more responsive than the factory setup. Bruce Roe bcroe@juno.com