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BRAKES
•
too t h i n , or i f m a c h i n i n g w o u l d cause rotor thickness
to f a l l below m i n i m u m thickness requirements.
Check r o t o r l a t e r a l r u n o u t a n d thickness v a r i a t i o n
i f pedal p u l s a t i o n or a n occaisional l o w pedal condi-
t i o n w a s experienced. Measure r u n o u t w i t h a d i a l i n -
dicator. Measure thickness w i t h a micrometer a t a
m i n i m u m o f four points around t h e b r a k i n g surfaces.
CHECKING
ROTOR MINIMUM
THICKNESS
Measure rotor thickness a t t h e center of the brake-
shoe contact surface. Replace t h e rotor i f i t is w o r n
below m i n i m u m thickness, or i f r e f i n i s h i n g w o u l d re-
duce thickness below t h e allowable m i n i m u m . Rotor
m i n i m u m thickness is usually specified on t h e rotor
h u b ( F i g . 19).
Fig. 19 Typical Location Of Rotor Minimum
Thickness Limit
ROTOR
RUNOUT
Check rotor l a t e r a l r u n o u t w i t h d i a l indicator C-
3339 as shown i n t h e top view (Fig. 20). Excessive
l a t e r a l r u n o u t w i l l cause brake pedal pulsation a n d
r a p i d , uneven wear of the brakeshoes. position t h e
d i a l indicator plunger approximately 25.4 m m (one
inch) i n f r o m t h e rotor edge.
B e s u r e w h e e l b e a r i n g
adjustment i s c o r r e c t
before c h e c k i n g rotor runout. I n c o r r e c t adjust-
m e n t c a n create a condition s i m i l a r to e x c e s s i v e
l a t e r a l runout.
M a x i m u m allowable rotor r u n o u t for a l l models is
.102 m m (.004 inch).
Fig. 20 Checking Rotor Runout And Thickness
Variation
ROTOR THICKNESS
VARIATION
V a r i a t i o n s i n rotor thickness w i l l cause pedal p u l -
sation, noise and shudder.
Measure rotor thickness a t 6 to 12 points a r o u n d
the rotor face (Fig. 20). Position t h e micrometer ap-
proximately 19.05 t o 25.4 m m (3/4 to one inch) f r o m
the rotor outer circumference for each measurement
as shown i n the bottom view ( F i g . 20).
Thickness should n o t vary by more t h a n .013 m m
(.0005 inch) from point-to-point o n t h e rotor. Refinish
or replace t h e rotor i f necessary.
ROTOR
REFINISHING
Rotor b r a k i n g surfaces can be refinished b y sand-
i n g and/or m a c h i n i n g i n a disc brake lathe. T h e lathe
m u s t be capable of m a c h i n i n g both rotor surfaces s i -
multaneously
w i t h
d u a l cutter
heads
( F i g . 21).
E q u i p m e n t capable o f m a c h i n i n g only one side a t a
t i m e w i l l produce a tapered rotor. The l a t h e should
also be equipped w i t h a grinder attachment or d u a l
sanding discs for f i n a l cleanup or l i g h t r e f i n i s h i n g
(Fig. 21).
I f t h e rotor surfaces only need m i n o r cleanup of
r u s t , scale, or scoring, use abrasive discs to clean u p
the rotor surfaces. However, w h e n a rotor is scored or
w o r n , m a c h i n i n g w i t h c u t t i n g tools w i l l be required.
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