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5-8
BRAKES
DIAGNOSIS AND TESTING (Continued)
contact occurs . If the condition is allowed to continue,
rotors and drums can become so scored that replace-
ment is necessary.
BRAKE CHATTER
Brake chatter is usually caused by loose or worn
components, or glazed/burnt lining . Rotors with hard
spots can also contribute to chatter. Additional causes
of chatter are out-of-tolerance rotors, brake lining not
securely attached to the shoes, loose wheel bearings
and contaminated brake lining.
THUMP/CLUNK NOISE
Thumping or clunk noises during braking are fre-
quently not caused by brake components. In many
cases, such noises are caused by loose or damaged
steering, suspension, or engine components. However,
calipers that bind on the slide surfaces can generate
a thump or clunk noise . In addition, worn out,
improperly adjusted, or improperly assembled rear
brake shoes can also produce a thump noise .
BRAKE LINING CONTAMINATION
Brake lining contamination is mostly a product of
leaking calipers or wheel cylinders, worn seals, driv-
ing through deep water puddles, or lining that has
become covered with grease and, grit during repair.
Contaminated lining should be replaced to avoid fur-
ther brake problems .
WHEEL AND TIRE PROBLEMS
Some conditions attributed to brake components
may actually be caused by a wheel or tire problem.
A damaged wheel can cause shudder, vibration and
pull. A worn or damaged tire can also cause pull.
Severely worn tires with very little tread left can
produce a grab-like condition as the tire loses and
recovers traction. Flat-spotted tires can cause vibra-
tion and generate shudder during brake operation . A
tire with internal damage such as a severe bruise,
cut, or ply separation can cause pull and vibration .
STOP LAMP SWITCH
Stop lamp switch operation can be tested with an
ohmmeter. The ohmmeter is used to check continuity
between the pin terminals at different plunger posi-
tions (Fig. 7).
NOTE : The switch wire harness must be discon-
nected before testing switch continuity .
SWITCH CIRCUIT IDENTIFICATION
" Terminals 1 and 2 are for broke sensor circuit.
" Terminals 5 and 6 are for th stop lamp circuit.
" Terminals 3 and 4 are not u:ed.
TERMINAL
PINS
TJ
J9405-88
Fig. 7 Stop Lamp Switch Terminal Identification
SWITCH CONTINUITY TEST
(1)
Check continuity between terminal pins 5 and
6
as
follows:
(a) Pull plunger all the way out to fully extended
position.
(b) Attach test leads to pins 5 and 6 and note
ohmmeter reading .
(c)
If continuity exists, proceed to next test.
Replace switch if meter indicates lack of continuity
(shorted or open) .
(2) Check continuity between terminal pins 1 and
2 as follows :
(a) Push
switch
plunger
inward
to
fully
retracted position .
(b) Attach test leads to pins 1 and 2 and note
ohmmeter reading.
(c) If continuity exists, switch is OK. Replace
switch if meter indicates lack of continuity (switch
is open).
RED BRAKE WARNING LAMP
The red brake warning light will illuminate under
the following conditions:
" 2-3 seconds at start-up as part of normal bulb
check.
" When parking brakes are applied .
" Low brake pedal caused by leak in front/rear
brake hydraulic circuit.
If the red light remains on after start-up, first ver-
ify that the parking brakes are fully released. Then
check pedal action and fluid level. A red light plus
low pedal indicates the pressure differential switch
and valve have been actuated due to a system leak.
On models with ABS brakes, the amber warning
light only illuminates when an ABS malfunction has
occurred. The ABS light operates independently of
the red warning light.
For addition information refer to Group 8W
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Troubleshooting
