Specifications
CALIPER
TO
ROTOR
CLEARANCE
I
WTRANSFER
TUBE
FIG.
5-Typical Disc Brake Assembly
to seal the cylinder bore from con-
tamination (Fig. 6). Square-section
rubber piston seals are positioned in
grooves in the cylinder bores.
The piston seals perform three im-
portant tasks:
1.
They provide hydraulic sealing
between the cylinders and pistons.
2.
They return the pistons to re-
leased position, when hydraulic pres-
sure is released.
3.
They maintain the shoes in cor-
rect adjustment at all times (com-
parable to the automatic adjusters in
drum-type brakes).
The cylinders are connected hy-
draulically by means of internal pas-
sages in the caliper housing and an
external transfer tube between the
two halves of the caliper assembly.
One bleeder screw and fluid inlet
fitting is provided on each caliper
assembly.
The shoe and lining assemblies are
located between parallel machined
abutments within the caliper, and
are supported radially by tabs on the
outer ends of the shoe assemblies
(Fig. 25). The shoes slide axially in
the caliper abutments by means of
the tabs which ride on machined
ledges (bridges) when hydraulic pres-
sure is applied to the piston (Fig.
6). A shoe and lining assembly con-
sists of friction material bonded to a
metal
platc called the shoe. It is re-
placed as a unit. Brake torque is ab-
sorbed by the mating of the shoe end
against the caliper abutments (Fig.
25). Two spring clips are attached to
the top of the caliper to retain the
FIG.
6-Typical Caliper Assembly-Sectional View
PISTON
1
BRAKES APPLIED
FIG.
7-Function of Piston Seal
shoe and lining assemblies. The cali-
per assembly is mounted to a bracket
located between the spindle and rotor
splash shield, to the front of the
wheel vertical centerline.
The cast iron disc is of the venti-
lated rotor type. incorporating forty
fins and is attached to, and rotates
with, the wheel hub. The outside
'
diameter of the rotor is 11.290 in-
ches and the inside diameter is 7.170,
inches. This type of design increases
cooling area and permits circulation
of air through the rotor resulting in
-
more rapid cooling of the brake. A
splash shield bolted to the spindle is
used primarily to prevent road con-
taminants from contacting the inboard
rotor and lining surfaces (Fig. 17).
The wheel provides protection for the
outboard surfaces of the rotor.
As the brake pedal is depressed,
hydraulic pressure from the master
cylinder forces the pistons out of the
caliper bores against their respective
shoe and lining assemblies. The
force of the pistons against the shoes
moves the linings against both sides
BRAKES RELEASED
til3m~
of the revolving rotor to effect brak-
ing action.
During brake application, the rub-
ber seal on each piston stretches as
the piston moves against the shoe
(Fig. 7). When the hydraulic pres-
sure against the piston is released,
the seal relaxes or rolls back. This
roll-back action pulls the piston away
from the shoe just enough to relieve
the force of the lining against the
rotor and, thereby, provide the re-
quired running clearance. Also, inher-
ent rotor
runout contributes to the
maintenance of running clearance.
Automatic adjustment is achieved by
the pistons sliding in the seals out-
ward from the cylinder bores. The pis-
ton gradually changes its position rela-
tive to the seal as the lining wears
and, thus, maintains the correct ad-
justment location at all times.
-
When the brakes- are in the un-
applied position, there is no hydrau-
lic pressure to the calipers because
the fluid source at the master cylin-
der by-passes the residual check
valve.