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(263)
BRAKES
REPAIRS
8-19
B
Figure 8-12-Machining Speciflcations for Standard Brake Drum
'---It---+-
THIS SURFACE MUST BE
SMOOTH & FREE FROM
CHATTER OR TOOl
MARKS.
RUNOUT MUST NOT
EXCEED
.00
5"
TOTAL INDICATOR
READING.
SERIES
A
B
40
-50
2'
/
32"
11.997
"
12.003
"
70
2'
/ ,,
"
11.997"
12.00
3"
LATERAL RUNOUT OF THIS
FACE MUST NO T
EXCEED
.030" TOTAL INDICA TOR
READING.
BALANCE_A.~~~~--,r-
WEIGHT
d. Out-of-Round Drum
An out-of-round drum makes accurate
brake
shoe adjustment
impossible
and is likel
y
t
o
cause ex
ces sive
wear of ot her parts of
brake
mechanism due to its eccentric
action.
An out -
of-round drum can also ca use
sever e
and
very
irregular tire tread wear.
A drum that is
more
than .010"
out-of-round
on the
diameter
is unfit for
service
and should
be rebored
(subpar.
e, below). Out- of-round,
as
well
as taper and wear can
be accurately
measured
with an inside
micrometer
fitted
with proper
extension
rods.
When measuring a drum for out-of-round,
taper, and wear, take
measurements
at the
open and closed
edges
of machined su
rface
and
be
polished
wit h fine
emery cloth
bu
t
sh
ould
not be rebored. At this
stage, eliminating t
he
grooves
in drum and sm
oothing
the ri
dg es
on
lining would ne
cessitate removal
of
too m
uch
metal
and
lining,
while if left
alone, the
grooves
and ri
dg es match
and
satisfactory
ser vice can
be obtained.
If
brake
linings a
r e t
o
be
replaced, a
g
rooved
drum should
be
r
ebored
for
use
wit h
ove
rsize
linings.
(subpar. e,
below).
A
grooved
drum,
if
used with new lining, will
not only wear
the
lining but will
make
it
difficult,
if not
impossi-
ble, to
obtain
efficient
brake performance.
c. Grooved Drum
If the brake linings are little worn and drum
is grooved, the drum should be rebored just
enough to remove grooves and the ridges in
the lining should be lightly removed with a
lining grinder.
If
brake linings are more than half worn,
but do not need replacement, the drum should
8-17 INSPECTING AND RECONDITION-
ING BRAKE DRUMS
Whenever brake drums are removed they
should be thoroughly cleaned and inspected for
cracks, scores, deep grooves, and out-of-round.
Any of these conditions must be corrected since
they can impair the efficiency of brake oper-
ation and also can cause premature failure of
other
parts.
a. Cracked Drum
A cracked drum is unsafe for further service
and must be
replaced.
Welding a cracked drum
is not recommended.
b. Scored Drum
Smooth up any slight scores by polishing
with fine emery cloth. Heavy or extensive scor-
ing will cause excessive brake lining wear and
it will
probably
be necessary to rebore in order
to true up the braking surface.
over end of anchor
'
pin, using"'large pliers and
being careful not to nick or distort springs.
6. Pry shoes
away
from backing plate and
lubricate shoe contact surfaces with a thin
coating of Bendix or
Delco
Brake
Lubricant,
or
Lubriplate. On
rear
brakes,
sparingly
apply
same lubricant
wh
ere brake cable contacts back-
ing plat e.
7. Install brake
drum and wheel. If working
on front
brake lubricate
and adjust front
wheel
bearings
(p
ar.
6-14)
. Remove
adjusting hole
cove
r
f
r om ba
cking plat e.
8. Centralize brake
shoes and set anchor pin,
then a
dj ust all
br ake
shoes and brake
cable
as
described
in
paragraph 8-15,
steps 17 through
22.
IMPORTANT:
Brakes
must not
be seve
rely
appl
ied
immediate ly
aft er
ins tallati on of
new
brak e
shoes or
lining s. Severe application
may
permanently
injure
new linings
and may score
brak e dru m s. When linings are new
th
ey must
be given m
odera te
use for seve
ra l day
s until
nicely burnished.
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