TRUCK SERVICE MANUAL
TRANSMISSION
HT 700D SERIES TRANSMISSIONS
Para 2-26
(7) Movement
of
the
selector
valve
q. Automatic Upshifts
determines the highest gear which will be normally
(1) When the transmission is operating in D5
reached automatically. In drive 5 (D5), automatic 1-2, 2-
a combination of rear governor pressure and modulator
3, 3-4 and 4-5 shifts can occur. In drive 4 (D4),
pressure, or rear governor pressure alone, will upshift
automatic 1-2, 2-3 and 3-4 shifts can occur. In drive 3
the transmission to the next gear. At closed, or part
(D3), automatic 1-2 and 2-3 shifts can occur. In drive 1
throttle, modulator pressure exists and will assist rear
(D1), no upshift can occur unless overspeed occurs.
governor pressure. At full throttle, there is no modulator
Automatic downshifts can occur within the selected
pressure. Thus, upshifts occur sooner when the throttle
ranges.
is closed; and is delayed by opening the throttle.
(8) The various drive ranges limit the highest
(2) Rear governor pressure is dependent
gear attainable by introducing a pressure which prevents
upon the rotational speed of the transmission output.
rear governor pressure from upshifting the signal valves
The greater the output (vehicle) speed, the greater is
(unless a governor pressure well above that normally
rear governor pressure. When rear governor pressure is
attained is reached). This pressure is a regulated,
sufficient, the first upshift (1-2) will occur.
reduced pressure derived from main pressure at the hold
regulator valve.
A FURTHER INCREASE IN REAR GOVERNOR
Main pressure is directed to the hold regulator valve
PRESSURE WILL CAUSE A 2-3 UPSHIFT.
through the hold feed line when the selector valve is at
drive 4 (D4), drive 3 (D3), or drive 2 (D2) position. The
A further increase in rear governor pressure (and vehicle
pressure produced in the hold regulator valve is directed
speed) will cause a
3-4 upshift. A still further
to the 4-5 shift signal valve when the selector valve is at
increase in rear governor pressure will cause a
' 4-5
drive 4 (D4). The hold pressure is directed to the 3-4
upshift. Note that each of these upshifts will be either
and 4-5 shift signal valves when the selector valve is at
delayed or hastened by the decrease or increase,
drive 3 (D3) position. With the selector valve in drive 2
respectively of modulator pressure.
(D2) position, the pressure is directed to the 2-3, 3-4 and
4-5 shift valves.
(3) In other drive ranges, the same upshift
sequence occurs until the highest gear attainable in that
(9) Hold regulator pressure at each shift
range selection is reached.
signal valve will push the upper valve upward, and raise
the pressure at which the lower valve will be pushed
(4) In any automatic upshift, the shift signal
upward by rear governor pressure. Thus, when hold
valve acts first. This directs a shift pressure to the relay
regulator pressure is present, no upshift can occur at that
valve. The relay valve shifts, exhausting the applied
shift signal valve, except at an elevated speed.
clutch and applying a clutch for a higher gear.
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