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5 - 4
BRAKES
•
PULL
A f r o n t p u l l condition could be t h e r e s u l t o f con-
t a m i n a t e d l i n i n g i n one caliper, seized caliper piston,
b i n d i n g caliper, loose caliper, loose or corroded slide
pins, improper brakeshoes, or a damaged rotor.
A
w o r n , damaged
wheel b e a r i n g or suspension
component are f u r t h e r causes of p u l l . A damaged
front t i r e (bruised, p l y separation) can also cause
p u l l .
A common and frequently misdiagnosed p u l l condi-
t i o n is where direction o f p u l l changes after a few
stops. T h e cause is a combination o f brake d r a g fol-
lowed b y fade a t one o f the brake u n i t s .
As the d r a g g i n g b r a k e overheats, efficency i s so re-
duced t h a t fade occurs. Since the opposite b r a k e u n i t
is s t i l l f u n c t i o n i n g n o r m a l l y , i t s b r a k i n g effect is
magnified. T h i s causes p u l l t o switch direction i n fa-
vor of t h e n o r m a l l y f u n c t i o n i n g brake u n i t .
W h e n diagnosing a change i n p u l l condition, r e -
member t h a t p u l l w i l l r e t u r n t o the o r i g i n a l d i r e c t i o n
i f the d r a g g i n g brake u n i t is allowed t o cool down
(and is not seriously damaged).
REAR BRAKE
GRAB OR PULL
Rear grab or p u l l is u s u a l l y caused by a n i m p r o p -
e r l y adjusted or seized p a r k i n g brake cable, contam-
inated l i n i n g , bent or b i n d i n g shoes a n d support
plates, or i m p r o p e r l y assembled components. T h i s is
p a r t i c u l a r l y t r u e w h e n only one rear wheel i s i n -
volved. However, w h e n both rear wheels are affected,
the master cylinder or p r o p o r t i o n i n g valve could be
at f a u l t .
BRAKES
DO NOT HOLD AFTER
DRIVING
THROUGH DEEP WA TER
PUDDLES
T h i s condition is generally caused b y water soaked
l i n i n g . I f the l i n i n g is only wet, i t can be d r i e d b y
d r i v i n g w i t h the brakes l i g h t l y applied for a m i l e or
two. However, i f the l i n i n g is both wet and d i r t y , dis-
assembly a n d cleaning w i l l be necessary.
BRAKE
NOISE
Squeak/Squeal
B r a k e squeak or squeal may be due to l i n i n g s t h a t
are wet or contaminated w i t h brake fluid, grease, or
o i l . Glazed l i n i n g s a n d rotors w i t h h a r d spots can
also contribute to squeak. D i r t and foreign m a t e r i a l
embedded i n the brake l i n i n g can also cause squeak/
squeal.
A very loud squeak or squeal is frequently a sign
of severely w o r n brake l i n i n g . I f the l i n i n g has w o r n
t h r o u g h to t h e brakeshoes i n spots, metal-to-metal
contact occurs. I f the condition is allowed to continue,
rotors can become so scored t h a t replacement is nec-
essary.
Thump/Clunk
T h u m p i n g or c l u n k noises d u r i n g b r a k i n g are fre-
q u e n t l y n o t caused b y b r a k e components. I n m a n y
cases, such noises are caused b y loose or damaged
steering, suspension, or engine components.
How-
ever, calipers t h a t b i n d o n t h e slide pins can gener-
ate a t h u m p or clunk noise. I n a d d i t i o n , w o r n out,
improperly adjusted, or i m p r o p e r l y assembled rear
brakeshoes can also produce noise a t h u m p noise.
Chatter
B r a k e chatter is usually caused b y loose or w o r n
components, or glazed/burnt l i n i n g . Rotors w i t h h a r d
spots
can also
contribute t o chatter. A d d i t i o n a l
causes o f chatter are out-of-tolerance rotors, brake
l i n i n g not securely attached t o the shoes, loose wheel
bearings and contaminated brake l i n i n g .
BRAKELINING
CONTAMINATION
B r a k e l i n i n g contamination is u s u a l l y a product o f
l e a k i n g calipers or wheel cylinders, d r i v i n g t h r o u g h
deep water puddles, or l i n i n g t h a t has become cov-
ered w i t h grease and g r i t d u r i n g repair.
WHEEL AND TIRE
PROBLEMS
Some conditions a t t r i b u t e d to b r a k e components
may actually be caused b y a wheel or t i r e problem.
A damaged wheel can cause shudder, v i b r a t i o n and
p u l l . A w o r n or damaged t i r e can also cause p u l l .
Severely w o r n tires w i t h very l i t t l e t r e a d left can
produce a grab-like condition as the t i r e loses and re-
covers t r a c t i o n .
Flat-spotted tires can cause v i b r a t i o n a n d wheel
t r a m p and generate shudder d u r i n g b r a k e operation.
A t i r e w i t h i n t e r n a l damage
such as a severe
bruise or p l y separation can cause p u l l a n d v i b r a t i o n .
MASTER CYLINDER/POWER BOOSTER TEST
(1) S t a r t engine a n d check booster v a c u u m hose
connections. Hissing noise indicates v a c u u m leak.
Correct any v a c u u m leak before proceeding.
(2) Stop engine a n d shift transmission i n t o N e u -
t r a l .
(3) Pump brake pedal u n t i l a l l v a c u u m reserve i n
booster is depleted.
(4) Press a n d hold brake pedal under l i g h t foot
pressure.
(a) I f pedal holds firm, proceed to step (5).
(b) I f pedal does not hold firm a n d falls away,
master cylinder is f a u l t y ( i n t e r n a l leakage).
(5) S t a r t engine and note pedal action.
(a) I f pedal falls away s l i g h t l y under l i g h t foot
pressure t h e n holds firm, proceed t o step (6).
(b) I f no pedal action is discernible, power
booster or vacuum check valve is f a u l t y . I n s t a l l
k n o w n
good check
valve
a n d repeat
steps (2)
t h r o u g h (5).
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