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BRAKE POWER UNIT
(PISTON TYPE)
DESCRIPTION
The
vacuum
power
cylinder (3,
Fig. 1)
con-
tains
the
power piston
(
19)
which
is
attached
to
the piston
rod (4)
and operates
against
a
re-
turn
spri
ng
(17
)
.
Attached to the cylinder is an
air
cleaner
(24) and a
vacuum
inlet tube
(1).
The
vacuum inlet
tube is
attached to the
piston
by
a
flexible
hose
(2).
Operating
within the piston
and
pi
sto
n rod are
the valve
rod
(6) poppet
as-
sembly 20),
and
valve rod balancing diaphragm
pin
(22)
and diaph
r
agm (23).
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14
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19
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20
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21
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23 -
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Brake pedal (14) pivots at point
(12)
which
is rigidly
supported
under the dash in the
driv-
er's compartment.
Trigger arm (7), which is an
integral part of
the
upper
portion
of the
brkke
pedal, is in contact
with the
end of valve rod (6)
of the
cylinder
piston.
Power lever (16),
shown
behind the brake pedal
lever
,
pivots on
the
brake
pedal lever at point ( 13). The
lower
end
of
the
power lever is attached to
the
end
of
master
cyl-
inder push
r
od
(15). The
upper
end of
the
power
lever
contains
pin (8) which is f
r
ee to slide to
97
the
right in
forked clevis
slot
(9).
The forked
clevis
slot is
integral with
piston rod
(4). Brake
pedal lever
(14) contains cam
pin
(11) which is
free to
move
in slot
(10) of
the
power
lever.
Cam
pin
(ll)
is designed
for
use in adjusting
the
position
of the
trigger
arm so
as to
give equal
travel to the
released
and to the applied posi-
t ions.
The brake pedal, valve
rod,
and
t
he
master
cylinder push rod are
held in the
released
posi-
tion by
spring (17).
OPERATION OF THE POWER
CYLINDER AND
REACTIONARY
LINKAGE
Released
Position
In
the released position (Fig.
1)
piston (19) is
held
to
the
left
by the
return
spring (18). Brake
pedal return spring (17)
acting through the
trigger arm (7)
holds
valve
rod (6)
to the lcft
compressing valve
rod
spring
(5),
and poppet
spring (21).
The
valve rod pushes poppet
as-
sembly
(20)
from
the atmosphere seat on pis-
ton
(19).
Vacuum is t
r
ansmitted
from the engine
in-
take
manifold to inlet
tube
(1),
through
the
hose (2), to the center of piston (19).
Atmosphere
enters
the left cylinder
cha mber
through air cleaner (24), passes
through
the
open
atmosphere
port
at the center of the piston
and
enters
the right cylinder chamber. In
the
released position,
atmosphere
pressure
exists
in
both chambers
of
the cylinder and the piston
is therefore
"atmosphere
suspended."
Applying
and
Holding
With
t.he initial
movement
of
brake
pedal (14),
trigger
arm (7) is moved to
the
right (Fig. 2),
allowing valve rod
spring
(5) to move
valve
rod (6) to the
right and
the poppet
assembly
(20) to seat against
the atmosphere
port in
the
piston.
The rod
spring
then pulls
the
rod
away
from
the
poppet assembly connecting
the right
cylinder
to vacuum.
Before the valve
r od
is
separated from the
poppet
assembly,
however, the pressure dif-
ferentia
l existi
ng across the rod must
be over-
come.
(The r ight
side
of the rod is under
at-
mosphere pressure
while
the left side
is sub-
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