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vacuum valve. With atmosphere closed off and
vacuum transmitted into
the
chamber,
the
bel-
lows
contract,
applying power to the brake
pedal
linkage through
the pull
yoke.
The
amount
of
power applied to the linkage
by the
power
unit
is
in direct proportion to
the
amou
nt
of
pressure
applied at
the
brake
pedaL
This
power assist, is,
in
effect,
a multiplication
of the operator's
pedal
pressure.
Poised
Position
As the
operator's pedal
pressure
is varied
to
suit his
braking requirements,
t
he
power
sup-
plied by
the unit varies in
proportion. At
any
point
during brake application or
release
(wher
e
the
operator
assumes a holding
posi-
tion) the
unit immediately becomes
"poised,"
ready to
respond to further
application
or
t
o
release
(Fig.15). In the poised position, both
the air
and
vacuum valves are closed and a
status quo
is
mainta
ined
in
the
air-vacuum
bellows.
A
further applying
moveme
nt
of
th
e
pedal
will cause
fu
rther
air evacuation
of
the bellows
to add
power to
application
.
As pedal
pressure
is
released, the
air valve
will open proportion-
ately to admit
air
to
the
bellows.
At any
point
between a
fully
released
and
a
fully
applied position, the unit will
instantly
become
"poised
"
whenever the operator holds
a constant pedal
pressure.
PISTON
TYPE
-
POWER UNIT
The description.
operation. disassembly and
assembly of the piston type power brake unit
can
be
found on page 97,
SERVICE
PROCEDURES
(Bellows
Type and Piston Type
Power Brake Units)
Removal of
Power Unit
Place a wood wedge between
the
power
brake
lever and the forward
edge of
the
triangular
hole in the
pedal bracket,
as shown
in
Fi gure
J
6. This will
prevent
the
trigger
arm
from
ex-
tending beyond the extremities
of
the
bra
cket.
16
,
Fig. 16
-
Removing
or
Installing Power Brake Unit
(Bellows
Type Shown)
.VOTE: I
f
pedal linkage
is
allolC€(l
to
extend
tllI'ollgh the hole
in
dash panel
I
he trigge?' ann
may be
damaged.
Disconnect
vacuum
hose at
power unit.
Remov
e
complete power unit
and
bracket
as-
.sembly
by removing the
fo
ur
hex nuts
and
lockwashers.
C~lreful1y
withdraw unit
from
dash panel, as
shown in
Figure 16.
.VOTE:
Use
cat'e to p1'Cvent loss of lIY/011 bush-
ings
011
pe<iul
linkoge
n'oss
pin.
Installation of Power Unit
Po!;ition
power unit on dash
pa nel of vehicle so
that
its axis inclines
down
toward front
of
ca
r
,
as illustrated
in Fig
ures
12
and 16.
N
OTE: As
yo
k
e
passes
through dash panel be
s//'
J "e that
it
engages
pedal
linkage conectly
by
.sliding
ove1' nylon
bushings 011 tile power
Make
lever
cross
pin,
Replace the fou
r
hex nuts and lockwashers.
Tighten
secu rely
amI
remove
wedge from
pedal
bracket.
REMOVAL OF PEDAL LINKAGE FROM
PEDAL BRACKET
(POWER UNIT INSTALLED)
Remove
brake
pedal
return
spring
and
master
cylinder push
rod
end
pin, Remove power brake
pedal lever
shaft.
,.j
!
1
1
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