65 Riv - TH400 - kickdown solenoid..how does it actually work?!

[moran75]

Hi all

Re my 65 Riv - TH400

Just for my own education...

I've attached a couple of pics of my kickdown solenoid/gasket and of the valve body it attaches to within transmission...

If i'm correct, when the solenoid is 'activated' it creates what i believe is called 'DET pressure' which acts on the 1 2 valve up in the valve body, thus kicking down?

How does the DET pressure get created?!

Re the little hole on underside of the solenoid as per first pic - is this closed when solenoid is activated, and resulting vacuum or change of pressure - DET pressure - acts on the 1 2 vale? Or is a component missing and something else happens?

Thanks in advance



Kevin (London, England)

 

[TODD]

Kevin, Detent pressure develops when the Detent valve opens. The feed for the Detent valve comes from a Drive pressure line. Drive pressure is created from Line pressure when the selector lever is moved to one of the three forward ranges. Detent pressure is regulated to a steady 70 psi.

Detent pressure is fed to the "back side" of the 1-2 Valve and the 2-3 Valve. The Detent pressure tries to close these valves, making them go to the lower gear. In addition, vehicle speed has to be under 70 mph before a 2-3 Detent Downshift can happen. Speed has to be under 20 mph before a 2-1 Detent Downshift can occur.

The Detent solenoid is normally de-energized, and the solenoid needle valve is seated, blocking any flow. A restricted passage from the Line pressure source feeds the solenoid valve and the Detent Valve. With the solenoid valve closed, Line pressure develops at the Detent Valve causing it to close. In this position, Drive pressure is cut off, and no Detent pressure develops.

When the solenoid is energized, the needle valve opens and exhausts the weak flow of Line oil. Then pressure at the Detent Valve drops so low that a spring opens it. With the Detent valve open, Detent lines go to 70 psi.

The Detent solenoid does not actually handle Detent oil. Instead it acts as a pilot valve that just controls the Detent Valve.

Attached are some drawings of the Detent components and connecting oil passages. Hope this helps.