Opel 1900 1973 Service Manual page 412

VACUUM MODULATOR
Figure Vacuum Modulator and Modulator Valve
decrease as car speed increases. For this reason, gov-
ernor pressure (which is a function of car speed) is
directed to the area between the two different diame-
ter spools at the outboard end of the valve. As gover-
nor pressure increases, it creates an outward force on
the modulator valve and in effect reduces the spring
force of the modulator assembly.
The modulator assembly consists of two chambers
separated by a diaphragm. The chamber toward the
valve is open to atmosphere and the other chamber
is connected to engine vacuum. The vacwm cham-
ber also contains a spring. When there is no vacuum
the diaphragm and is transmitted to the valve
through a plunger. This is the spring force which
establishes the regulated pressure of the modulator
valve. As the vacuum in the outer chamber increases,
an outward force is created on the diaphragm which
cancels out some of the spring force. This continues
up to 16" of vacuum, at which point the diaphragm
force cancels out the spring force and the modulator
pressure becomes zero.
In summary, the following indicates the function of
the total modulator system in combination with the
pressure regulator system.
In addition, higher car speeds will produce a some-
what lower modulator and line pressure for any
given vacuum by virtue of the governor pressure
acting on the modulator valve.
Engine Vacuum
Torque
Low High
High
L o w
Modulator Line
L o w LOW
High High
AUTOMATIC TRANSMISSION
Modulator pressure is then directed to:
Pressure regulator boost valve.
2 - 3-Shift control valve by way of the 3 - 2 control
valve.
Detent Valve.
Low Speed Downshift Timing Valve.
Detent Pressure Regulator
The regulating action of the Detent Pressure Regula-
tor Valve is essentially the same as for the Modulator
Valve, except that it regulates a constant pressure.
See Figure 7C-32. The feed port, regulating port and
exhaust port all function in the same manner as the
Modulator Valve. Since the force set up by the pres-
sure in the regulating port acts only against a fixed
spring force, the resulting detent pressure is con-
stant. The detent regulator pressure is directed to the
Detent Valve and to the Manual Low and Reverse
Control Valve.
D E T . PRESS.,REG.
Figure Detent
l-2 Accumulator Valve
The I 2 Accumulator Valve, Figure 7C-33, is used
to establish a desired pressure to ultimately control
the rate of apply of the second clutch during a I to
2 upshift. Here again, the regulating action is essen-
tially the same as for the Modulator Valve or Detent
Pressure Regulator Valve.
Valve
Pressure Regulator Valve