In any downshift the signal acts first and exhausts the shift signal
pressure that is holding the shift valve up.
The shift then moves
down and exhausts the applied clutch and applying the clutch for the
next lower range.
When operating the transmission in low (L) or reverse (R), the
transmission downshifts at a higher vehicle speed than in "drive."
Hold pressure, applied to the 1-2, 2-3, and 3-4 signal valves, causes
these transmission downshifts at a higher vehicle speed. A decrease
or increase in modulator pressure does not affect the automatic
upshifts when the selector is in "low" or "reverse."
Automatic Shift Circuit.
f. G1 Governor Circuit (fig. 1-53).
The G1 governor circuit
originates at the front pitot. Rotation of the vane pitot collector
ring, located on the forward clutch housing, directs oil against and
into the pitot orifice.
This produces a pressure in the front
governor circuit that varies with the rotational speed of the
collector ring. This pressure is applied to the bottom of the lockup
shift valve and front pitot modulating regulator.
g. Lockup Shift Circuit (fig. 1-54).
When front governor
pressure (or front governor pressure assisted by modulator pressure)
overcomes spring pressure and compresses the spring at the top of the
valve, the lockup shift valve moves up. In this position, the valve
directs pressure through the lockup cutoff valve to the lockup piston
and causes the lockup clutch to engage. To apply the lockup clutch,
the transmission uses clutch apply pressure from the engaged range