Ford Thunderbird 1966 - Page 15

2-8
GROUP 2
-BRAKES
CALIPER
HOUSING
CALIPER
TO ROTOR
CLEARANCE
TRANSFER TUBE
-ROTOR
PISTON
OUST
BOOT
RETAINING
GROVE
PISTON
SEAL
FIG.
2
Caliper
Assembly
Sectional View
outer ends of the
shoe assemblies
(Fig. 21).
The shoes slide
axially
in
the caliper abutments
by
means
of
the
tabs
which
ride
on
machined ledges
(bridges)
when hydraulic
pressure is
applied
to the piston
(Fig.
7).
A shoe
and
lining assembly
consists
of
fric
tion
material bonded to a metal plate
called
the
shoe.
It is replaced as a
unit. Brake torque is absorbed
by
the
mating
of the
shoe end against the
caliper
abutments
(Fig. 21).
A splash
shield is attached to
the
top
of
the
caliper
to
retain the
shoe and
lining
assemblies and
reduce contamination.
The
caliper
assembly
is
mounted
on
the front
wheel spindle to
the rear of
the
wheel
vertical centerline.
The
cast
iron
disc
is of the
ventilat
ed
rotor type
incorporating forty
fins
and is
staked
to,
and
rotates
with,
the
wheel
hub. The
outside diameter
of
the
rotor is 1
1 .87 inches and
the inside
diameter
is
7.875
inches. This type
of
design
increases
cooling
area and
per
mits
circulation
of air
through the
rotor
resulting
in
more rapid
cooling
of the
brake. A
splash
shield
bolted to
the
spindle
is
used
primarily
to
prevent road
contaminants
from con
tacting
the
inboard
rotor and
lining
surfaces
(Fig.
8). The
wheel provides
protection
for
the
outboard
surface
of
the
rotor.
OPERATION
As
the
brake
pedal is
depressed,
hydraulic
pressure from
the
master
cylinder forces
the
pistons
out
of the
caliper bores
against
their
respective
shoe and
lining
assemblies.
The
force
of
the pistons
against
the shoes
moves
the linings
against
both sides of
the re
volving
rotor
to
effect
braking
action.
During
brake
application,
the rub
ber seal in each piston
stretches as the
piston moves
against the shoe
(Fig.
3). When the
hydraulic pressure
against the piston
is
released,
the seal
relaxes
or rolls
back. This roll-back
action
pulls
the
piston
away
from
the
shoe
approximately
0.005
inch
to
relieve the force of
the
lining
against
the rotor
and, thereby,
provide
the
required
running
clearance.
Also,
in
herent rotor
runout contributes
to the
maintenance
of
running
clearance.
Automatic
adjustment
is achieved
by
the
pistons
sliding
in
the
seals out
ward from the cylinder bores.
The pis
ton
gradually
changes its position rel
ative
to
the seal
as the
lining
wears
and,
thus,
maintains the correct
ad
justment
location at all
times.
PISTON
t
When
the
brakes
are
in the
unap
plied
position,
there
is
no
hydraulic
pressure
to
the
calipers
because
the
fluid
source
at
the
master
cylinder
by
passes
the
residual
check
valve.
A
proportioning
valve located
between the
master
cylinder
and the
rear
brake
wheel cylinder
provides
bal
anced
braking
action between
the
front and
the
rear brakes under a
wide
range
of
braking
conditions (Fig. 16).
By
regulating
the hydraulic
pressure
applied to the
rear wheel
cylinders,
the
valve
limits
rear
braking
action
when
high
pressures are
required at
the
front
brakes. In this
manner,
pre
mature
rear
wheel skid is
prevented.
The
proportioning
valve is serviced
as
an
assembly
and
is
never
adjusted
or
overhauled.
SELF-ADJUSTING
BRAKE
ASSEMBLIES-REAR WHEELS
The
self-adjusting
brake mechanism
consists
of a
cable,
cable
guide,
adjust
ing
lever,
adjusting
screw
assembly,
and
adjuster
spring
(Fig. 4).
The
cable is hooked
over the anchor pin
at
the
top
and is connected to the lever
at
the
bottom. The cable
is connected
to
the
secondary
brake shoe
by
means
of the
cable guide.
The
adjuster
spring
is
hooked to
the
primary
brake shoe
and to
the lever. The
automatic ad
juster
operates
only
when the
brakes
are
applied while the
car
is
moving
rearward and
only
when the secon
dary
shoe is free to move
toward
the
drum beyond
a predetermined point.
With the
car
moving
rearward
and
the
brakes
applied,
the
wrap-around
action
of
the
shoes
following
the
drum
forces the
upper end of
the
primary
shoe
against the anchor
pin. The
ac
tion of the
wheel
cylinder
moves
the
upper
end of
the
secondary
shoe
away
CALIPER
HOUSING
BRAKES APPLIED
BRAKES
RELEASED
HI
370-
A
FIG. 3
-Function
of
Piston
Seal