Buick LeSabre 1965 Service Manual page 535

BRAKES
TROUBLE DIAGNOSIS 9 - 1 3
imbedded particles of metal, etc.,
on surface. Sand or brush the af-
fected surface—do not use any
liquid cleaning a g e n t . Linings
having oil, grease, or hydraulic
fluid on linings cannot be cleaned
satisfactorily and must be re-
placed (par. 9-10).
(7) Loose Brake Backing Plate.
Tighten all backing plates.
(8) Unequal Camber. If car has a
tendency to lead to one side when
driven on a level road it will also
pull to one side when brakes are
applied. Adjust camber to speci-
fied limits (Group 7).
k. Brakes Squeak
(1) Brake Drum Condition. Care-
fully inspect brake drums for out-
of-round, scoring or cracks. Re-
bore any drum if out-of-round or
scored (par. 9-11), Replace any
drum which is cracked or has
hard spots in braking surface.
(2) Foreign Material Imbedded in
Lining. Metallic particles or grit
imbedded in brake lining will
cause squeaking. Sand the sur-
faces of linings and remove all
particles of metal. In some cases
it may be necessary to dress the
lining surfaces with a portable
resurfacing machine in order to
properly clean the surfaces and
insure good contact with brake
drums.
(3) L i n i n g s Loose on Brake
Shoes. Replace any rivets that
are loose. Lining must be tightly
held against brake shoe flange,
particularly at t h e ends (par.
9-10).
(4) Bent Brake Backing Plate.
True up or replace backing plate.
(5) Improper Brake Shoe Lining.
Install standard Buick Lining or
equivalent (par. 9-10).
(6) Shoes Scraping on Backing
Plate. Squeaking or " c r u n c h "
will be produced if contact sur-
faces are dry, rusty, or rough.
The noise is more pronounced if
brake shoes have considerable
movement due to large clearance
between shoes and drums. Clean,
smooth up, and lubricate contact
surfaces and reduce shoe move-
ment by adjusting to safe mini-
mum clearance (par. 9-10).
(7) Shoes Slapping Against Back-
ing Plate. If drums have been
re-turned with a noticeable lead,
shoes tend to follow lead and
produce a regular slapping noise
against backing plate during brake
application. Polishing drums with
light emery cloth will reduce
noise.
I. Brakes Fade (Fail to Hold)
The condition known as "fade"
is caused by loss of friction be-
tween brake lining and drums as
a result of abnormally high lining
temperatures. E x c e s s i v e heat
cooks out the most volatile in-
gredients of the bonding material
in lining and t h i s acts as a
lubricant.
Excessive l i n i n g temperatures
will be produced by partial or
spotty contact of linings with
brake drums, due to improper
adjustment. E x c e s s i v e lining
temperature also can be caused
by frequent and heavy braking at
high speed, driving with parking
brakes partially applied, "riding"
the brake pedal, or prolonged use
of brakes on steep grades without
using low range to obtain adequate
engine braking.
After a set of brakes have faded
a few times it is probable that
they will continue to fade even
though the shoes have been ad-
justed to establish full contact of
linings with drums. This is be-
cause the cooking out of bonding
ingredients h a s destroyed t h e
frictional properties of the lining
surfaces. If the lining thickness
is ample and the cooking process
has not been prolonged, it may
be possible to obtain a correction
and some useful life by grinding
off about .020" from the lining.
Merely sanding off the lining sur-
face will not remove destroyed
lining material. If this cannot be
done, replacement of lining is the
only remedy.
The u s e of improperly com-
pounded linings will also produce
fade. Some replacement linings
lose their frictional properties
at lower temperatures than the
linings selected for Buick brakes.
Such linings must be replaced.
When brake drums are rebored
too thin they will have excessive
expansion due to heat. The result
is loss of pedal reserve and brak-
ing when drums are hot, and good
brakes when drums are cold. This
may be erroneously diagnosed as
fade, but fade occurs with ample
pedal reserve.