e. Automatic Shifts (fig. 1-52).
The following
paragraphs
describe the automatic upshift and downshift process.
(1) Upshifts. When operating the transmission in drive (D), a
combination of G2 governor pressure and modulator pressure, or G2
pressure alone will upshift the transmission to the next range.
At closed or part throttle, modulator pressure exists and assists G2
governor pressure. At full throttle, there is no modulator pressure;
therefore, upshifts occur at a lower vehicle speed when the throttle
is closed and at a higher vehicle speed when the throttle is fully
open.
Rear governor pressure depends upon the rotational speed of the
transmission output; therefore, the greater the output (vehicle)
speed, the greater the G2 governor pressure.
When G2 governor
pressure is sufficient, the 2-3 shift occurs. A further increase in
rear governor pressure (and vehicle speed) causes the 3-4 shift.
NOTE:
A decrease in modulator pressure delays the next upshift, as
an increase in modulator pressure hastens the next upshift.
In any automatic shift, the signal acts first.
This directs the
shift signal pressure to the shift valve, causing the valve to move
up, and exhausts the applied clutch and applying a clutch for a
higher range.
When operating the transmission in low (L) or reverse (R), the
transmission upshifts 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 upshifts at a higher vehicle speed. A decrease or
increase in modulator pressure does not affect the automatic upshifts
when the selector is in "low." To inhibit any upshifts to third or
fourth ranges in reverse, the transmission applies reverse pressure
to the spring side of the 2-3 and 3-4 shift valves.
(2) Automatic downshifts. When operating the transmission in
drive (D), G2 governor pressure and modulator control the automatic
downshifts, just as they controlled upshifts.
Downshifts occur in
sequence as G2 pressure, or modulator pressure, or both, decrease.
Low modulator pressure (open throttle) decreases the time between
downshifts; thus, high modulator pressure (closed throttle) delays
downshifts.
51
OD1710
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