PART
2-1 -
General Brake Service
2-3
pair
or
adjustment
due to
inability
of
the parking brake
to
hold against
moderate vehicle movement. Perform
tests
of the
parking brake system
and
controls after making certain
the
link-
age
and
manual controls operate
properly.
Diagnosis
of
vacuum release
sys-
tems
is
basically similar
to
electrical
diagnosis. That
is, the
vacuum
sys-
tem must
be
complete from
the
source
to the
vacuum components.
Any leaks, like
a bad
connection will
make
the
system inoperative.
If a
leak
develops
in one of the
vacuum
sys-
tems,
one or all of the
vacuum
com-
ponents
may
become inoperative. This
would
be
dependent
on the
location
of
the vacuum leak.
If the
leak
is in the
vacuum supply,
all
systems will
be-
come inoperative.
If the
leaks
is in
the component side
of the
vacuum
control
for the
specific system,
all
other systems will operate when
the
leaking system
is off.
When testing
a
parking brake
vacuum release system,
a
minimum
of
10 inches
of
vacuum
(Hg.)
should
be
available
at all
points where vacuum
is applied. This
can be
checked with
a Rotunda Fuel Pump Tester
Gauge (ARE345)
and two
Distributor
Tester hose adapters (Marked
Q)
connected together with
a
coupling.
This allows
the
Fuel Pump Tester
Gauge hose
to be
adapted
to any
other vacuum hose
or
rubber connec-
tor
in
the vacuum systems.
Failure
to
maintain
10
inches
of
vacuum
(Hg)
during vacuum system
tests could
be
caused
by a
loose hose
connection, resulting
in a
vacuum
leak. When checking
for
vacuum
be-
tween
two
points, trace
the
hose along
the entire routing
to be
sure
it is not
crossed with another hose
and con-
nected
to the
wrong connection.
All
of the
vacuum parking brake
control checks
are to be
performed
with the engine running
at
idle speed.
Leaks
in the
parking brake hoses
or
a
disconnected
or
improperly
con-
nected hose
can
usually
be
found
by
listening
for a
hissing sound along
the hose routings. Under
no
circum-
stances should
air
pressure
be
applied
to
the
vacuum system
as the
actuator
diaphragm
in the
parking brake
vac-
uum motor may be damaged.
1.
Start
the
engine
and run it at
idle speed. With
the
transmission
shift control
in
neutral, depress
the
parking brake pedal
to
apply
the
parking brake. Move
the
transmission
shift control
to D
range
and ob-
serve
the
parking brake pedal
to see
that
the
pedal moves upward
and the
parking brake releases.
If the
parking
brake releases,
the
parking brake
vacuum control
is
working properly.
2.
If the
parking brake does
not
release, test
for
vacuum
at the
steering
column neutral switch port
in the
junction block, vacuum lines
and the
parking brake release vacuum motor.
Use
the
Rotunda Vacuum
and
Fuel
Pump Tester
345.
This
can be
accomplished
by
removing
the
hose
from each component
and
attaching
it
to the
vacuum gauge. Connect
two
distributor tester vacuum hose adapters
together with
a
coupling
as a con-
nector
to
attach
the
gauge.
A
mini-
mum
of ten
inches
of
vacuum
is re-
quired
to
actuate
the
parking brake
vacuum motor.
Do not
remove
any
of
the
vacuum hoses from the junction
block unless
the
junction block
is
being replaced,
as the
plastic nipples
are thin
and
very brittle
and
damage
may result.
If a
minimum reading
is
not
present when checking each
of
the
aforementioned components,
they must
be
replaced.
ROAD TEST
A road test should
be
conducted
only when
the
operator
is
sure
the
brakes will stop
the
vehicle.
During
a
road test, apply
the
vehicle brakes
at a
road speed
of
20
mph for all
problem conditions
listed
in
Figs.
9 and 10
with
the ex-
ception
of
those resolved
in the
brake
system tests
and
brake chatter.
To
check
for
brake chatter
or
surge,
ap-
ply
the
brakes lightly
at 50
mph.
For
each
of the
symptoms encountered
check
and
eliminate
the
caused which
are listed
in
Figs.
9
and
10.
If
the
road test reveals
one or
more problem conditions listed Figs.
9
and 10,
correct
all
malfunctions
of
the vacuum system, brake booster
and hydraulic system prior
to
remov-
ing brake drums, brake calipers,
brake shoes
and
linings
or
backing
plates.
COMMON ADJUSTMENTS AND REPAIRS
PARKING BRAKE LINKAGE
ADJUSTMENT
Check
the
parking brake cables
when
the
brakes
are
fully released.
If
the
cables
are
loose, adjust them
as
follows:
1.
Fully release
the
parking brake
pedal
by
pulling
the
release lever,
or
on
a
vacuum release pedal
by
pushing
down
the
manual release lever.
2.
Depress
the
parking brake pedal
until
it is
engaged
in the
first notch
of
the control,
3.
Raise
the
vehicle. With
the
transmission
in
neutral, turn
the
adjusting
nut
forward against
the
equalizer
(Fig. 3)
until
a
moderate
drag
is
felt when turning
the
rear
wheels (approximately
100 lbs of
force
at the
outside diameter
of the
tire
is
required
to
turn
the
REAR WHEEL CABLE-2A809
EQUALIZER-TO-CONTROL CABLE-2A815
RiARWHiiUCAIUi=2A63i
ADJUSTING
NUT
HI
537-
A
rear FIG. 3—Parking Brake Adjustment
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