Booster In Released Position; Holding Position; Released Position; Parking Brake Control Assembly - Ford Thunderbird 1964 Shop Manual

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-