Buick LeSabre 1965 Service Manual page 542

9 - 2 0 DRUMS
BRAKES
and swings off the wheel spindle
or axle shaft may be used to grind
shoes concentric with drums, or a
bench mounted grinder may be
used to grind shoes to the proper
radius (.010" less than drum
radius). The i n s t r u c t i o n s of
equipment manufacturer must be
carefully followed.
9. Check all backing plate bolts
to make sure they are tight.
10. Lubricate front wheel bear-
ings, if necessary. Install front
hub and drum assemblies and ad-
just wheel bearings.
11. install brake drums. Remove
all adjusting hole covers.
12. Install all wheels, turn ad-
justing screws to provide an equal
two-hand drag and back-off 30
notches (par. 9-7).
13. Remove jacks and road test
car for proper brake action.
CAUTION: Brakes must not be
severely a p p l i e d immediately
a f t e r installation of reground
brake shoes or linings. Severe
application may permanently in-
jure new linings and may score
brake drums. When linings are
new they must be given moderate
u s e for s e v e r a l days until
burnished.
9 - 1 1 INSPECTING AND
RECONDITIONING
BRAKE DRUMS
Whenever brake drums are re-
moved 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
operation and also can cause
premature failure of other parts.
a. Cracked, Scored, or
Grooved Drum
WARNING: A cracked drum is
unsafe for further service and
must be replaced. Do not attempt
to weld a cracked drum.
Smooth up any slight scores by
polishing with fine emery cloth.
Heavy or extensive scoring will
cause excessive brake lining wear
and it will probably be necessary
to rebore in order to true up the
braking surface.
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 re-
placement, the drum should be
polished with fine emery cloth
but should not be rebored. At
this stage, eliminating the grooves
in drum and smoothing the ridges
on lining would necessitate re-
moval of too much metal and
lining, while if left alone, the
grooves and ridges match and
satisfactory s e r v i c e can be
obtained.
If brake linings are to be re-
placed, a grooved drum should be
rebored for use with oversize
linings (subpar. c, following). A
grooved drum, if used with new
lining, will not only wear the lin-
ing but will make it difficult, if
not impossible, to obtain efficient
brake performance.
b. Out-of-round or
Tapered Drum
An out-of-round drum makes ac-
curate brake shoe adjustment im-
possible and is likely to cause
excessive wear of other parts of
Brkke mechanism due to its ec-
centric action. An out-of-round
drum can also cause severe 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. c, below). A
drum that has more than .005"
taper should be rebored. 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 surface
and at right angles to each other.
Standard drums are machined to
an inside diameter of 11.997" to
12.022", with runout of braking
surface held within .005" total
indicator reading.
c. Reboring Brake Drum
If a drum is to be rebored, enough
metal should be removed to obtain
a true, smooth braking surface.
If a drum does not clean-up when
rebored to a diameter of 12.080",
it must be replaced. Removal of
more metal will affect dissipation
of heat and may cause distortion
of the drum.
A newly bored drum should always
have center contact with the shoes
on initial break-in, thus insuring
greater uniformity in brake per-
formance with l e s s danger of
brake pulling. To get this de-
sired position, the shoe radius
should always be .010" less than
the drum radius (or .020" less
on the diameter). This fit may be
accomplished by either grinding
the shoes or boring the drums,
whichever is the more practical.
If cleaning up a drum requires
boring to a size larger than
12.050", then .030" oversize lin-
ing must be used.
Fit between the brake shoes and
the drum must always be the
same on both sides of the car to
get equal braking action.
Brake drums may be refinished
either by turning or grinding.
Best brake performance is ob-
tained by turning drums with a
very fine feed. Too coarse a
feed will cause a condition on the
car called "shoe slap" in which
the shoes attempt to follow the
spiral of the cut, then snap back
against the backing plate. Ground