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BRAKES
5 - 3
(3) D u r i n g road test, make n o r m a l and f i r m b r a k e
stops i n 25-40 m p h (40-64 Km/h) range. Note f a u l t y
brake operation such as p u l l , grab, drag, noise, l o w
pedal, h a r d pedal, fade, pedal pulsation, etc.
(4) Inspect suspect brake components a n d refer t o
problem diagnosis i n f o r m a t i o n for causes o f various
brake conditions.
COMPONENT
INSPECTION
F l u i d leak points and dragging brake u n i t s can
u s u a l l y be located w i t h o u t r e m o v i n g a n y compo-
nents. The area around a leak p o i n t w i l l be w e t w i t h
f l u i d . The components
a t a dragging b r a k e
u n i t
(wheel, t i r e , rotor) w i l l be quite w a r m or h o t to t h e
touch.
Other brake problem conditions w i l l require compo-
n e n t removal for proper inspection. Raise t h e vehicle
and remove the necessary wheels for better v i s u a l ac-
cess.
DIAGNOSING BRAKE PROBLEMS
PEDAL FALLS
AWAY
A brake pedal t h a t falls away under steady foot
pressure is generally the result o f a system l e a k . T h e
leak point could be a t a brakeline, f i t t i n g , hose, or
caliper. I n t e r n a l leakage i n t h e master
cylinder
caused by w o r n or damaged piston cups, m a y also be
t h e problem cause.
I f leakage is severe, fluid w i l l be evident a t or
around t h e l e a k i n g component.
However i n t e r n a l
leakage i n t h e master cylinder w i l l not be physically
evident. Refer to t h e cylinder test procedure i n t h i s
section.
LOW
PEDAL
I f a low pedal is experienced, p u m p t h e pedal sev-
e r a l times. I f the pedal comes back up, w o r n l i n i n g
and w o r n rotors or drums are t h e l i k e l y causes.
A decrease i n fluid level i n the master cylinder res-
ervoirs may only be the result of n o r m a l l i n i n g wear.
F l u i d level can be expected to decrease i n p r o p o r t i o n
to wear. I t is a result of t h e o u t w a r d movement o f
caliper and wheel cylinder pistons to compensate for
n o r m a l wear. Top off t h e reservor
fluid
level a n d
check brake operation to verify proper operation.
SPONGY
PEDAL
A spongy pedal is most often caused by a i r i n t h e
system. T h i n brake drums or substandard b r a k e
lines a n d hoses can also cause a spongy pedal. T h e
proper course of action is to bleed t h e system and re-
place t h i n drums and suspect q u a l i t y brake lines a n d
hoses.
HARD PEDAL OR HIGH PEDAL
EFFORT
A h a r d pedal or h i g h pedal effort m a y be due t o
l i n i n g t h a t is water soaked, contaminated, glazed, or
badly w o r n . The power booster or check valve could
also be faulty. Test t h e booster a n d valve as de-
scribed i n t h i s section.
BRAKE
DRAG
B r a k e drag occurs w h e n t h e l i n i n g is i n constant
contact w i t h t h e rotor or d r u m . D r a g can occur a t
one wheel, a l l wheels, fronts only, or rears only. I t is
a product of incomplete brakeshoe release. D r a g can
be m i n o r or severe enough to overheat t h e l i n i n g s ,
rotors and drums.
B r a k e drag also has a direct effect o n fuel economy.
I f undetected, m i n o r brake drag can be misdiagnosed
as a n engine or transmission/torque converter prob-
lem.
M i n o r drag w i l l u s u a l l y cause s l i g h t surface char-
r i n g o f the l i n i n g . I t can also generate h a r d spots i n
rotors a n d drums from t h e overheat-cool down pro-
cess. I n most cases, t h e rotors, drums, wheels a n d
t i r e s are quite w a r m t o t h e touch after t h e vehicle is
stopped.
Severe drag can char t h e brake l i n i n g a l l t h e w a y
t h r o u g h . I t can also distort and score rotors a n d
d r u m s to t h e point of replacement. T h e wheels, tires
and brake components w i l l be extremely hot. I n se-
vere cases, the l i n i n g may generate smoke as i t chars
f r o m overheating.
Some common causes of brake drag are: seized or
i m p r o p e r l y adjusted p a r k i n g brake cables, loose/worn
wheel bearing, seized caliper or wheel cylinder pis-
t o n , caliper b i n d i n g on corroded bushings or rusted
slide surfaces, loose caliper m o u n t i n g bracket, d r u m
brakeshoes
b i n d i n g on w o r n or damaged
support
plates, or misassembled components.
I f brake drag occurs a t a l l wheels, the problem m a y
be related to a blocked master cylinder r e t u r n port or
f a u l t y power booster (binds-does not release).
BRAKE
FADE
B r a k e fade is a product of overheating caused by
brake drag. However, brake overheating a n d subse-
quent fade can also be caused by r i d i n g t h e brake
pedal, m a k i n g repeated h i g h deceleration stops i n a
short t i m e span, or constant b r a k i n g on steep m o u n -
t a i n roads. Refer to t h e Brake D r a g i n f o r m a t i o n i n
t h i s section for additional causes.
PEDAL PULSA TION
Pedal pulsation is caused by components t h a t are
loose, or w o r n beyond tolerance l i m i t s .
Disc brake rotors w i t h excessive l a t e r a l r u n o u t or
thickness v a r i a t i o n , or out of round brake d r u m s are
t h e p r i m a r y causes of pulsation. Other causes are
loose wheel bearings or calipers and w o r n , damaged
tires.
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