Chapter 12 Disc Brake System Components and Operation 205
Figure 12-26. An electric type pad wear sensor. A—Pad with
the sensor inside the lining and a dashboard warning light.
B—Brake pads in position and sensor wire lead harness with
connector. When the worn pads allow the sensor to contact the
rotor, the electrical circuit is complete. The dashboard light will
come on alerting the driver. (Bendix)
Brake
warning
light
Sensor
A
B
To brake warning
light
Wire harness
connectors
Sensor wire
leads
Brake
pads
Figure 12-25. A spring steel lining wear indicator. A—Pads are
new; the wear indicator is not able to contact the rotor. B—Pads
have worn down permitting the wear indicator to contact the
rotor. A high pitched squeal sound is being produced. This alerts
the driver that brake service is necessary. (Chevrolet)
Rotor Wear
indicator
Pad
rivet
Shoe
New
pad
A B
Squeal
sounds
Worn
pad
Figure 12-27. In the future, calipers similar to the one shown
here may be operated by electric motors. (Delphi)
Electric Calipers
In the future, calipers may be operated by electric
motors. Such a caliper will resemble a hydraulic caliper,
Figure 12-27. The pads will be pressed against the rotor by
the rotation of a small high-speed electric motor operating
through a worm drive. No hydraulic system will be needed.
The motor will be energized through a control module that
responds to sensor inputs, typically brake pedal pressure
and wheel speeds. The anti-lock brake system will be built
into the control module.
Summary
Disc brakes use a rotor or disc that provides a braking
surface for the pads. The rotor also aids in cooling. Rotors
are round and come in many different diameters and thick-
ness. They are constructed from cast iron and are either
solid or ventilated with fins between braking surfaces. The
rotor must be thick enough to absorb heat, and flat enough
to provide for smooth stops. The rotor is protected by a
splash shield.
Calipers are constructed of cast iron or aluminum.
They are either floating or fixed. The floating type can
move in relation to the spindle. Fixed types are solidly
bolted onto the spindle. Rubber dust boots protect the pis-
tons from water and dirt.
Floating calipers have one or two apply pistons. Fixed
calipers on newer vehicles are usually aftermarket units
with two or four pistons. The pistons on all calipers are
moved outward by hydraulic pressure. The piston seals are
used to return the piston to its unapplied position when
brake pressure is released. Some future calipers may be
operated by electric motors.