Chapter 12 Disc Brake System Components and Operation 203
Figure 12-22. A—Brake lining-to-shoe attachment using rivets.
B—Bonded brake lining-to-shoe. (Bendix)
Rivets
Bonded
lining
Figure 12-21. Brake pads come in all sizes, shapes, and
materials. (Jack Klasey)
Lining
Shoe
A
B
coefficient of friction with acceptable wear, smoothness,
and quiet operation. The lining absorbs heat and trans-
fers it to the shoe assembly. The shoe provides a rigid
area for the piston(s) to push against. Disc brake pads are
made in many shapes and sizes.
Lining Construction
Linings are made of heat resistant materials, as dis-
cussed in Chapter 11. The lining is constructed by mixing
the various temperature resistant and bonding materials.
This mixture is carefully controlled to create the proper
coefficient of friction. The mixture is then placed in a mold,
compressed, and heated. The finished pad is machined to
give it a smooth surface. Some pads are grooved to aid
in self-cleaning, air transfer for cooling, and noise reduc-
tion. The groove also acts as a wear indicator. When the
pad is worn until the groove is gone, the lining should be
replaced.
Shoe Construction
The shoes to which the linings are attached are made
of flat, heavy gauge steel, punched and formed to match
the caliper mounting and lining. Some shoes have align-
ment dowels stamped into the metal. Anti-rattle springs or
clips which reduce brake squeal may be riveted or welded
to the shoe. Some clips are snapped on the shoe, and must
be installed or transferred from the old shoes when new
shoes are installed.
Lining-to-Shoe Attachment
The lining is attached to the shoe in one of two ways.
One method is riveting. Brass rivets are used to attach the
lining to the shoe. The lining and shoe are made with a
number of matching holes, with the rivets installed through
the holes. The rivets are then secured tightly using the
proper riveting tools. Brass rivets are used since they will
not cause as much damage if the lining wears down until
they contact the rotor. A riveted shoe can have anywhere
from two to eight rivets. A riveted brake pad is shown in
Figure 12-22A.
The second method of lining attachment is called
bonding. Bonding is a process that glues the lining to
the shoe. A special high temperature cement or epoxy
resin is placed between the lining and shoe. Then the
lining and shoe are pressed together until the cement is
thoroughly dried or cured. Some cements require heat to
properly dry and hold. A typical bonded lining is illus-
trated in Figure 12-22B.
Noise Reduction Devices
Common brake noises are squeaks and squeals from
brake shoe and rotor contact, and clicks and knocks from
loose pad to caliper contact. Various clips, springs, and
other devices are attached to the brake pad shoe to reduce
noise. When the pad is installed on the vehicle, these
form a tension fit with the pad and other parts of the brake
assembly. The springs and clips absorb some of the vibra-
tions and noise from the pad as it rubs against the rotor.
Other designs use a piece of flexible heat resistant
material, sometimes called an insulator, installed on the
back of the pad. This material also absorbs noise and vibra-
tion. When used, they are installed on the outboard pad,
against the caliper housing. Some designs have insulators
on both pads, while others use a flat metal plate called an
anti-rattle clip, plate, or shim. Figure 12-23 shows differ-
ent noise reducing clips, springs, and shims.
Anti-Squeal Compounds
Companies that make gaskets and adhesives for auto-
motive use also produce chemically-based anti-squeal