PART
2-2-BRAKE
SYSTEM
2
-7
FIG. 2-Cutaway View of Vacuum
power brake application or release
in accordance with the foot pressure
applied to the valve operating rod
through the brake pedal linkage. The
control valve consists of a single
poppet with an atmospheric port and
a vacuum port. The vacuum port
seat is a
part of the valve hub and
diaphragm plate assembly. The at-
mospheric port seat is a part of the
valve plunger which moves within
the vacuum power diaphragm as-
sembly.
3.
A hydraulic master cylinder
which contains all of the elements
of the conventional brake master cyl-
inder except for the hydraulic
push-
rod which has a self locking adjust-
ment screw at one end with a piston
head at the other end.
The vacuum power diaphragm
and the components which make up
the valve assembly are connected to
the brake pedal through the valve
operating rod and pedal linkage. The
valve operating rod is connected to
the valve plunger which moves with-
in the power diaphragm assembly.
A valve return spring holds the valve
plunger and rod in the released posi-
tion when pressure is released from
the brake pedal. The valve poppet
is of the flexible
rubber type and is
supported by the valve body. In the
released position, the poppet return
spring holds the poppet against the
atmospheric port seat. A synthetic
rubber seal is used to seal the open-
ing between valve body sleeve and
the rear shell. Vacuum is supplied
to the booster through a vacuum
check valve located in the front
shell. Air for operation is admitted
through the air cleaner located at the
Booster
end of the valve sleeve. A rubber
guard attached to a flange on the
rear shell and over the air cleaner
protects the valve housing and seal
sleeve against dirt.
A
seal located in
the front vacuum chamber seals the
opening between the vacuum cham-
ber and the hydraulic plunger. The
hydraulic push rod forms the link
between the vacuum power dia-
phragm assembly and the hydraulic
piston of the master cylinder.
RELEASED POSITION
With the engine running and the
brakes released (Fig.
3),
vacuum
from the intake manifold is admitted
through the check valve to the front
(constant vacuum) chamber of the
power unit. In the released position
(no pressure applied to the brake
pedal), the valve operating rod and
valve plunger are held to the right
in the valve housing by the valve
return spring to CLOSE the atmos-
pheric port and OPEN the vacuum
port. With the valve in this position,
the rear (control vacuum) chamber
is also open to vacuum through the
porting in the vacuum diaphragm
and valve housing assembly. The
vacuum power diaphragm is then
"balanced" or suspended in vacuum,
since vacuum is present on both sides
of the power diaphragm. With the
power diaphragm balanced in vac-
uum, the diaphragm return spring
holds the diaphragm and hydraulic
push rod in the fully released posi-
tion. With the hydraulic push rod
in this position, the hydraulic com-
pensating port in the hydraulic mas-
ter cylinder is OPEN to permit brake
fluid to either return from the brake
system to the fluid reservoir or enter
the brake system from the fluid reser-
voir to compensate for any gain or
loss in fluid volume.
APPLIED POSITION
When the brakes are applied (Fig.
4),
the valve operating rod and valve
VACUUM PORT OPEN
/
ATMOSPHERIC SOURCE
I
ATMOSPHERIC
PRESSURE
FIG. 3-Booster in Released Position
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