Table of Contents
Advertisement
5 - 24
BRAKES
•
DISC BRAKE
OPERATION
The significant feature o f single piston caliper op-
eration is t h a t t h e caliper is free t o move l a t e r a l l y on
the slide surfaces.
A t brake application,
fluid
pressure i s exerted
equally against the caliper piston a n d a l l surfaces of
the caliper piston bore.
Pressure applied t o t h e piston i s t r a n s m i t t e d d i -
rectly to the inboard brakeshoe pressing t h e shoe l i n -
i n g against t h e rotor. A t t h e same t i m e , pressure
applied to t h e caliper bore surfaces, causes t h e cali-
per t o slide i n w a r d l a t e r a l l y . T h e i n w a r d movement
presses t h e l i n i n g o f t h e outboard shoe against t h e
opposite side o f the rotor to complete b r a k i n g action.
The application or release of fluid pressure causes
only a very s l i g h t movement o f t h e caliper and pis-
ton. A t brake release, t h e piston a n d caliper r e t u r n
to the non-appled position. The brakeshoes do not re-
t r a c t a n appreciable distance f r o m t h e rotor. The
m i n i m a l r u n n i n g clearance between t h e l i n i n g and
rotor provides improved response a n d reduced pedal
t r a v e l ; I t also helps i n p r e v e n t i n g d i r t and foreign
m a t e r i a l f r o m lodging between t h e shoe a n d rotor
surfaces.
DISC BRAKE LINING WEAR
COMPENSATION
N o r m a l l i n i n g wear is compensated for b y exten-
sion o f the caliper piston and by l a t e r a l movement of
the caliper i n the adapter. Piston position is also de-
t e r m i n e d i n p a r t by t h e square c u t piston seal (Fig.
4).
N o r m a l disc brake l i n i n g wear w i l l cause the cali-
per piston to extend enough to m a i n t a i n proper pedal
h e i g h t and brake response. The caliper bore w i l l re-
ceive the e x t r a fluid needed to compensate for the ad-
d i t i o n a l piston extension.
As the piston extends d u r i n g b r a k e application, the
square-cut seal is deflected o u t w a r d (Fig. 4). W h e n
brake pressure is released, t h e seal straightens and
r e t u r n s to a n o r m a l relaxed position. A l t h o u g h t h e
amount of seal movement is quite s m a l l , i t is enough
to retract the piston to the necessary m i n i m u m r u n -
n i n g clearance.
As l i n i n g wear occurs, t h e fluid level i n t h e front
brake reservoir w i l l decrease. T h i s is a n o r m a l con-
d i t i o n and o n l y requires adding enough fluid to re-
store proper level. However, w h e n t h e brakeshoes are
replaced a n d t h e caliper pistons bottomed i n t h e
bores, t h e added fluid must be compensated for to
avoid
o v e r f i l l
a n d overflow.
Removing
a s m a l l
amount of fluid from the front b r a k e reservoir before-
h a n d w i l l prevent this condition.
DISC BRAKE INSPECTION
Inspect t h e disc brake components whenever t h e
caliper a n d brakeshoes are removed d u r i n g service
operations or routine maintenance.
PISTON
CALIPER
DUST BOOT
RN102
Fig. 4 Caliper Piston Seal Operation
Check condition o f the rotor, brakeshoe l i n i n g , cal-
iper a n d brake hoses. F r o n t wheel bearing adjust-
m e n t and condition can also be checked a t t h i s t i m e .
The bearings should be repacked and adjusted i f nec-
essary.
Brakeshoes
W i t h t h e caliper a n d brakeshoes on t h e vehicle,
check r u n n i n g
clearance
between
t h e rotor a n d
brakeshoes. T h e shoe l i n i n g should either be i n very
l i g h t contact w i t h t h e rotor or have a m a x i m u m o f
.127 m m (.005 inch) r u n n i n g clearance. I f clearance
exceeds the stated amount, apply the brakes several
times and recheck clearance. I f clearance is s t i l l ex-
cessive, either t h e shoes are severely w o r n or t h e cal-
iper piston could be b i n d i n g i n t h e bore.
Hoses And Adapter
Inspect condition o f the b r a k e lines and hoses. Re-
place either f r o n t hose i f cut, t o r n , or the reinforcing
fabric is visible. Check condition o f the m e t a l brake-
lines. Replace a n y line t h a t is badly rusted, l e a k i n g
or damaged i n any way.
Clean and lubricate the slide surfaces of the caliper
and adapter. Use Mopar h i g h temperature grease for
t h i s purpose. Also verify t h a t t h e caliper adapter
bolts are secure and t i g h t e n e d t o proper torque.
Fluid Level
Check t h e master cylinder
fluid
level. M a i n t a i n
fluid level t o the bottom o f t h e indicator r i n g s on t h e
reservoir. Note t h a t f r o n t disc b r a k e fluid level can
be expected to drop s l i g h t l y as n o r m a l l i n i n g wear
occurs. Use Mopar brake fluid or equivalent m e e t i n g
SAE a n d D O T standards J1703 a n d D O T 3. Use
clean brake fluid f r o m a sealed container only.
Rotors
Check the rotor surfaces for excessive wear, discol-
oration, scoring, rust, scale, or cracks. Also look for
damaged or severely rusted v e n t i l a t i n g segments. I f
pedal pulsation was experienced, check wheel bear-
i n g adjustment a n d condition. I f t h e bearings are
O K , also check rotor r u n o u t a n d thickness v a r i a t i o n .
Advertisement
Table of Contents
