Buick LeSabre 1965 Service Manual page 524

9 - 2 DESCRIPTION
BRAKES
b. General Specifications (Cont'd)
Brake Pedal Height Adjustment, Standard and Power None
Static Pressure in Hydraulic System when Brakes are Released. 8 to 16 lbs.
Number of Brake Shoes at Each Wheel 2
Brake Type Self Energizing-Servo
Brake Shoe Lining Type 1 pc. Molded-Riveted
Front Shoe Lining Width x Minimum Thickness 2.25" x .220" Primary: 2.25" x .254 Secondary
Rear Shoe Lining Width x Minimum Thickness 2.00" x .220" Primary: 2.25" x .254 Secondary
Front Brake Drum, All Series Except 45000 Finned Aluminum with C.I. Liner
Front Brake Drum, 45000 Finned Cast Iron
Master Cylinder Piston Dia., Standard and Power 1"
Wheel Cylinder Size, Front 1 1/8"
Rear 1"
Approved Hydraulic Brake Fluid GM or Delco Super No. 11 or equiv.
Fluid Level, Below Lip of Reservoir Opening 1/8"
Shoe Adjusting Screw Setting, from Point where Wheels can just
be turned by hand Back Off 30 Notches
Brake Drum Inside Diameter, New 11.997" to 12.022"
Brake Drum Rebore, Max. Allowable Inside Diameter 12.080"
Max. Allowable Taper, Before Rebore .005"
Max. Allowable Out-of-Round, Before Rebore .010"
Max. Allowable Out-of-Balance of Drum 3 in. oz.
Max. Allowable Space Between Lining and Shoe Rim after Riveting . .005"
9 - 2 DESCRIPTION OP
BRAKE MECHANISM
The brake mechansim includes a
brake drum and a brake assembly
at each wheel, and two separate*
and independent control systems
for applying the brakes— (1) Park-
ing brake control system (2) Serv-
ice brake control system with
self-adjusting mechanism.
a. Wheel Brake Assemblies
All rear brake drums consist of a
cast iron rim fused to a pressed
steel disk. The cast iron rim pro-
vides an ideal braking surface and
increases brake lining life. Ex-
ternal ribs and fins aid in dissi-
pation of heat.
Front brake drums on the 46, 48,
49000 Series are cast aluminum
alloy with a cast iron liner. The
aluminum section has ribs and
fins for better heat dissipation
while the cast iron liner provides
the best braking surface. The
lighter 45000 Series has finned
all-cast iron drums.
The brake assembly at each wheel
uses a primary (front) and sec-
ondary (rear) b r a k e shoe of
welded steel construction, with
one-piece lining attached by tu-
bular rivets. The primary shoe
lining is shorter and thinner, than
the secondary shoe lining and is
of different composition; there-
fore the two shoes are not inter-
changeable. See Figure 9-1.
Each brake shoe is held against
the backing plate by a hold-down
spring, pin, and cup which allow
free movement of the shoe. The
notched upper end of each shoe is
held against the single fixed an-
chor pin by a heavy coil spring.
An adjusting screw and lock
spring connects the lower ends of
both shoes together and provides
adjustment for clearance with the
brake drum.
ACTUATING
PIVOT
OVER-RIDE
SPRING
ACTUATOR
ACTUATOR
RETURN SPRING
ADJUSTING
SCREW
Figure 9-1—Right Rear Wheel
Brake Assembly
A h y d r a u l i c wheel cylinder
mounted on the backing plate be-
tween the upper ends of the brake
shoes forces the shoes against the
brake drum when the service
brakes are applied. On rear
wheels only, a lever mounted on
each secondary shoe and con-
nected to the primary shoe by a
strut is used for applying the
shoes when used as parking
brakes. See Figure 9-1.
When the brake shoes contact the
rotating drum, in either direc-
tion of car travel, they move
with the drum until the rear-
ward shoe is stopped by the an-
chor pin and the forward shoe
is stopped by the rearward shoe
through the connecting adjusting
screw. Frictional force between
drum and shoe lining tries to
rotate each shoe outward around
its anchor point but the drum it-
self > prevents this rotation; con-
sequently the shoes are forced
more strongly against the drum
than the applying force is pushing
them. See Figure 9-2. It is also
evident that the force applied by
the drum to the forward shoe is
imparted to the rearward shoe
through the connecting adjusting
screw.