PART
2-1-GENERAL
BRAKE SERVICE
2-3
DIAGNOSIS
GUIDE—POWER
BRAKES VACUUM
BOOSTER—FRAME
MOUNTED
BRAKE PEDAL KICKS
BACK WHEN APPLIED
ROUGH ENGINE IDLE
WITH BRAKES RELEASED
ROUGH ENGINE IDLE
OR
STALL
AND
HARD PEDAL
WITH BRAKES APPLIED
INTERMITTENT HARD
BRAKE PEDAL
HARD
PEDAL—BOOSTER
DIAPHRAGM RUPTURED
BRAKES
DO NOT
RELEASE
This condition
may be
caused
by
Replace
the
slave cylinder piston
a defective hydraulic piston check and/or piston
cup.
valve
or
slave cylinder piston
cup.
Check
for
vacuum leaks
in the
required. This condition
may
also
vacuum line, loose hose connections,
be
caused
by
vacuum leaks
at the
a loose body clamp,
or a
weak con- control valve diaphragm, at the valve
trol
valve piston return spring. piston assembly,
or
at the power dia-
Check
all
connections
and
tighten
phragm.
Remove
and
overhaul
the
them
or
replace damaged parts
as
booster assembly.
Check
the
condition
of the air
valve plate,
or
the
control valve pis-
cleaner.
If
it is clogged with
dirt,
re-
ton
not seating properly
on
the plate
place
the
air cleaner felt.
A
sticking
may
also cause this condition.
In ad-
control
valve piston, leaks
at the
dition,
the
booster diaphragm
may
control valve diaphragm
or
atmos-
be
damaged. Remove
and
overhaul
pheric valve
seal,
dirt
on
the
control
the
booster assembly.
Check for
an
obstructed air clean- draulic fluid. Clean
or
replace darn-
er,
a
defective vacuum check
valve,
aged parts, refill
the
hydraulic
sys-
or
a
slave cylinder piston sticking
in
tem
with
new
heavy-duty type brake
the bore
due
to
dirt
or
inferior
hy-
fluid,
and
bleed
the
system.
When
a
ruptured diaphragm
is
premature failure.
found,
check
for
gasoline odor
on
Gasoline can get
on
the diaphragm
the diaphragm. Gasoline will deteri- from
the
intake manifold if the vac-
orate
the
diaphragm
and
cause
a
uum
check valve is defective.
Check
the
rear
of the
vacuum control valve piston holds the brakes
chamber
for
damage. This condition
in an
applied position, disconnect
may also
be
caused
by a
sticking
the
booster vacuum line from
the
control valve piston,
a
faulty slave vacuum check valve
and
install
a
cylinder piston check valve, dirty pipe plug
in
the
check valve open-
brake
fluid,
a
sticking slave cylinder ing. This permits
the
brakes
to
re-
piston,
a
sticking push
rod,
or a
lease. Manual application
of
brakes
faulty check valve
in the end
cap. may
then be made without assistance
Remove
and
overhaul the booster. from
the
booster.
In case
of
emergency, if
a
sticking
DIAGNOSIS
GUIDE—POWER
BRAKES VACUUM
BOOSTER—DASH
MOUNTED
HARD PEDAL
Check
as
follows
to see if the
Brake pedal linkage sticking.
power unit is operating: With the en- Faulty vacuum check valve.
gine stopped, depress
the
brake Collapsed
or
leaking vacuum hose.
pedal several times
to
eliminate
all
Plugged vacuum fittings
vacuum from
the
system. Apply
the
Ud
^
Qg vacuum chamber
brakes,
and
while maintaining
pres-
,
r
,
.
, ,
, , .
.,
°
.
Vacuum check valve stuck
in
sure
on
the
pedal, start
the
engine.
, ,
., .
y
.
, ,
b
,
closed position.
If
the
unit is
operating,
the
brake
,,-,,,
pedal will move forward slightly Leak
,n
bellows assembly.
when engine vacuum power is added Diaphragm assembly
out
of
place
to
the
foot pressure
on
the pedal.
If
ln
housing locating radii:
the unit
is
not
operating, there will Vacuum leak
in
automatic trans-
be
no
pedal action. mission
T.V.
vacuum line connec-
If
this check shows that
the
unit tion
or
fitting.
is
not
operating, check
for the
fol-
Vacuum leak
in
forward,
vacuum
lowing: housing.
CONTINUED
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