Ford Thunderbird 1964 - Booster in Released Position; Holding Position; Released Position; Parking Brake Control Assembly

2-8
GROUP
2
BRAKES
VACUUM
SOURCE
BELLOWS
ATMOSPHERIC
SOURCE
DIAPHRAGM
ATMOSPHERIC
VALVE
VACUUM
PORT
OPEN
o
BRAKE
ATMOSPHERIC
PORT
CLOSED
PI
VACUUM
f\F?)
ATMOSPHERIC PRESSURE
PEDAL
VALVE HUB
H1207-A
FIG.
4
Booster in Released Position
HOLDING
POSITION
When
the forward motion of
the
brake
pedal
is stopped
and
held,
the
valve
operating
rod
ceases
to
move
the control
valve
plunger
forward.
However,
the
unbalanced
forces
of
atmospheric
pressure and vacuum
on each
side of the
diaphragm will
continue to
move the outer
sleeve
of the
control
valve
plunger for
ward
keeping
the
vacuum
porting
closed. At
the same
time,
the
re
action
force
acting
through
the
reaction
ring
and
lever
assembly
will
tend
to
move the
atmospheric
valve
to the closed position (Fig. 3). When
these
combined forces
balance,
the
porting
to the
vacuum
supply
will
remain
closed and the
atmospheric
valve
will cut
off
any
further
passage
of atmospheric
pressure
to
the
area
behind the diaphragm.
Therefore,
the power assist force
acting
on
the
master
cylinder piston will
stabilize
and
the hydraulic
force
applying
the brakes
will be
maintained at a
constant
level.
RELEASED
POSITION
When the
pedal pressure is
re
leased
from the
valve
operating
rod
PEDAL
MOUNT
VACUUM
POWER
UNIT
*
PISTON
LINK TV
\
7
PEDAL
ASSEMBLY
RELEASE
LEVER
LEFT
SIDE
VIEW
RIGHT
SIDE VIEW
H1312-A
FIG.
5-Parking
Brake
Control
Assembly
and
plunger
assembly,
the
plunger
return
spring
moves
the
plunger
away
from the
atmospheric
valve
allowing
the
valve
to
seat
against
the hub
(Fig.
4). This
seating
of
the
valve
closes
off
the
bellows
chamber
from
the
hub
porting
that
connects
to
the
rear
side
of
the
dia
phragm.
At
the
same
time,
the
rear
ward
movement
of
the
plunger
opens
the
porting
from the
vacuum
cham
ber
and
draws
out
the
air
from
the
rear
side
of
the
power
diaphragm.
With
vacuum on
both sides
of
the
diaphragm,
the
assist
force
against
the
master
cylinder
push rod is
eliminated.
The
brake
shoe
retract
ing
springs
will,
therefore,
cause
the
hydraulic
fluid to
return the
master
cylinder
piston,
push
rod,
control
valve
plunger
assembly
and
the
dia
phragm to
the
released
position.
With
the
piston
and push
rod
in
the
released
position,
the
hydraulic
compensating
port
in
the
master
cylinder
is
open.
The
open port
per
mits
fluid
either to
return
from
the
brake
system to
the
fluid
reservoir,
or enter
the
brake
system
from the
reservoir.
PARKING
BRAKES
An
independent foot
-
operated
parking
brake
control actuates
the
rear
wheel brake
shoes through
a
cable
linkage. The
operating
cable
is
routed
from the
parking
brake
control
assembly
to
the
equalizer
lever which is
attached to
the
equal
izer
assembly. The rear
brake cables
connect the
equalizer
assembly
to
the
parking
brake lever at
each
rear
secondary
shoe
(Fig.
1,
Part 2-1
and
Fig. 15).
When the pedal
is
depressed the
secondary
brake shoes are
forced
against
the rear brake
drums. The
pedal
is
held
in the applied
position
by
the engagement
of a
spring-
loaded pawl with a
ratchet
in the
control
assembly.
A
vacuum
power unit
will
release
the
parking
brakes
automatically
when the
transmission
selector
lever
is
moved into
any
drive position
with the
engine running.
The brakes
will not
release
automatically,
how
ever,
when
the selector lever is
in
the
neutral or
park position
with
the
engine
running,
or
in
any
position
with
the
engine off.
The
parking
brake
control
as
sembly
is
mounted to
the
left
cowl
side panel
(Fig.
15). The pedal
as-