Additional force can be provided to force a 2-1 downshift under "kickdown" conditions.
This is provided by the kickdown portion of the kickdown/throttle valve combination.
When the accelerator is fully depressed, the kickdown valve closes off the exhaust from the kickdown circuit and also forces the throttle valve to the end of its bore.
In this position, the throttle valve can no longer regulate the incoming line pressure and throttle pressure now becomes equal to line pressure and passes into the kickdown circuit leading to the kickdown port at the 1-2 shift valve.
Fluid passes across the valley area and onto the spring end of the plunger.
The force provided overcomes governor pressure and moves the shift valve back to the 1st gear position.
This releases the front band by opening its apply circuit and exhausting the apply fluid back to the pan.
However, as road speed rises governor pressure will increase and since it is acting on the large differential area on the bottom land, will eventually become high enough to force the valve upwards and overcome kickdown pressure.
This keeps engine RPM within safe limits in the automatic range.
