Pontiac FIREBIRD 1972 Service Manual page 1427

15-12 1972 PONTIAC SERVICE MANUAL
REGULATOR ASSEMBLY
The regulator (Fig. 15-10) controls the amount of engine
vacuum going to the servo. An electrical impulse from the
engaging switch vents engine vacuum to the atmosphere,
the size of the opening being varied by a governor. The
governor is driven by a cable from the transmission with
a transfer gear driving the speedometer cable in a 1
:
1 ratio.
The following are the main operating components of the
regulator:
SOLENOID VALVE AND COUPLING COlL
The solenoid valve (Fig. 15-1 1) blocks the vacuum supply
to the Cruise Control when the unit is not in operation.
When its magnetic field is energized (Cruise Control oper-
ating), the vacuum source to the regulator is completed.
When the coupling coil is not energized, the coil itself
moves in relation to governor speed. When the coil is
energized, a vacuum regulator plate moves with the cou-
pling coil.
The drive cable from the transmission connects directly to
the regulator drive assembly to turn the governor shaft
and weights, including the cable to the speedometer.
VALVE BODY AND MAGNET ASSEMBLY
As the governor weights move
in
or out with varying car
speed, the actuator cup assembly causes the coupling coil
to move. This portion of the Cruise Control is always
operating regardless of whether the system is engaged or
not.
When the driver pushes the engaging switch, the vacuum
plate is held to the coupling valve by the coupling valve
coil magnetic field. The position in which the vacuum
plate is held to the coupling coil is dependent upon the car
speed when the system was engaged. This position does
not change as car speed is increased (system over-ridden),
and hence acts as a memory device for when cruise is
resumed.
When the switch is engaged, the solenoid valve coil is also
energized pulling the valve off its seat and opening port
"M" to port "S". As car speed increases or decreases,
causing the governor weights to go out or in, the actuator
will move the coupling coil and vacuum plate. The
vacuum plate will now regulate engine vacuum by opening
the vacuum port to atmosphere. This regulated vacuum is
delivered from the vacuum plate to the "S" outlet on the
bottom of the regulator, then through a hose to the
vacuum servo. The servo then moves in proportion to the
vacuum applied from the regulator and thus varies throt-
tle opening through the cable to the throttle lever.
V A C U U M CHECKS
The vacuum servo is a sealed unit; therefore, a leaky or
defective bellows requires replacement of the assembly.
I
COUPLING COIL GOVORNOR
f
SOLENOID VALVE
Fig. 15-1 1 Regulator-Internal View
Utilize engine vacuum to test for leakage as follows:
1. Disconnect vacuum servo cable from accelerator
linkage and hose from regulator assembly. Connect
engine vacuum directly to vacuum servo.
2. Note position of vacuum servo diaphragm.
3.
Start engine. The bellows should pull in.
4.
Clamp off engine vacuum supply and check for leak-
age.
The vacuum brake release switch and all vacuum connec-
tion hoses can be checked in a similar manner by utilizing
a vacuum source.
ELECTRIC CLOCK
DESCRIPTION
The electric clock operates on direct current from the car
battery and must not be compared too closely for accuracy
to a home electric clock operating on alternating current.
The cycles per second of alternating current used in the
home are controlled and periodically corrected at the
power house, thereby eliminating accumulation of errors.
With the direct current system, no such control is possible;
therefore, automobile electric clocks will accumulate er-
rors day by day the same as handwound, spring-operated
clocks.