
5- 2 BRAKES
•
Fig.
2
Vacuum Switch Location
Thevacuumchamberisconnectedtothebooster
checkvalvebya vacuumsupply
hose.
A wire
har-
ness
connects
theswitch
sensor
tothebrakewarning
light.
Ifboostervacuumfallsbelow8.5inchesfor
8-10
seconds
ormore,theswitch
sensor
completes
the
circuit
tothewarning
light
causingitto
illumi-
nate.
VACUUM
PUMP
DIAGNOSIS
Vacuum
pumpdiagnosisinvolvescheckingpump
output
with
a vacuum
gauge.
Thelowvacuumwarn-
ing
switchcan
also
bechecked
with
a vacuum
gauge.
Refertothediagnosisprocedureinthissection.
A
standardvacuum
gauge
canbe
used
tocheck
pumpoutputwhen
necessary.
Simplydisconnectthe
pumpsupply
hose
andconnecta vacuum
gauge
to
theoutletportfortesting
purposes.
Vacuumshould
hold
steady
ina
range
ofapproximately8.5to25
inchesatvariousengine
speeds.
DIAGNOSING
LOW
VACUUM
OUTPUT
CONDITION
A
lowboostervacuumconditionora
faulty
low
vacuumwarningswitch
will
cause
thebrakewarn-
ing
light
to
illuminate.
If
the
light
does
goonandin-
dicates
theexistenceofa lowvacuumcondition,
checkthevacuumpump,boosterandwarningswitch
as
follows:
(1)
Checkvacuumpumpoilfeed
line.
Verify
that
line
connectionsare
secure
andnotleaking.Ifleak-
ageisnotedandpumpisnoisy,replacepump.
(2)
Checkvacuumpumpoutput
with
a standard
vacuum
gauge.
Disconnectthesupply
hose
tothe
booster.
Connectthe
gauge
tothis
hose
andrunthe
engineatvariousthrottleopenings.Outputshould
range
from
8.5to25inchesvacuum.Ifvacuumis
consistentlybelow8.5inches,theproblemis
with
the
vacuum
hoses
ora vacuumpumpcomponent.Ifout-
putis
within
specified
limits,
continuetesting.
(3)
Checkboosteroperationasdescribedinthedi-
agnosis
section.
Replace
thecheckvalve,vacuum
hoses,
orbooster
if
necessary.
However,
if
boosterop-
erationiscorrectbutthewarning
light
is
still
on,
continuetesting.
(4)
Disconnectthevacuum
hose
from
thewarning
switch,
plugthe
hose
andconnecta handvacuum
pumptotheswitch.
(5)
Startandruntheengine.
(6)
Apply
8.5to9 inchesofvacuumtothewarning
switch
and
observe
thewarning
light.
Ifthe
light
goes
out,theswitchvacuum
hose
iseitherlooseor
leaking.
Ifthe
light
remainson,leavetheengine
running
andcontinuetesting.
(7)
Apply
20-25inchesvacuumtotheswitchand
observe
warning
light
operation.Ifthe
light
now
goes
out,theswitchisatfaultandshouldbere-
placed.Ifthe
light
remainson,continuetesting.
(8)
Reconnectthevacuum
hoses
andreplacethe
original
warningswitch
with
a knowngoodswitch.
Run
theengineand
observe
warning
light
operation.
If
the
light
isnowoff,theoldswitchis
faulty.
Ifthe
light
remainson,theproblemisinthe
wiring
be-
tweentheswitchandwarning
light.
REMOVING
VACUUM-STEERING
PUMP
ASSEMBLY
(1)
Disconnectbatterynegativecable.
(2)
Positiondrainpanunderpowersteeringpump.
(3)
Disconnectvacuumandsteeringpump
hoses
from
respectivepumps(Fig.3).
Fig.
3
Vacuum
And
Steering
Pump
Hose
Connections
(4)
Disconnectoil
pressure
sender
wiresat
sender
(Fig.
4).