194 Auto Brakes
Figure 12-3. A rear disc brake rotor which incorporates internal
fins and cross-drilled (side-to-side) air holes. These air holes
aid in cooling the rotor. (Porsche)
Drilled
rotor
surface
Internal fins
Figure 12-4. A brake rotor which is secured to the hub with wheel studs. Study the construction. (Chrysler)
Braking rotor
Bolt-on
brake rotor
Wheel stud holding
rotor to hub
Hub
Inner bearing
Outer bearing
Spindle
Shoe and lining
Wheel
Caliper
Boot
Seal
Piston
Mounting bolt
Adapter
Seal
Mounting bolt
Splash shield
Steering knuckle
A variation of the ventilated rotor has both internal fins
and holes drilled into the braking surfaces from one side to
the other. This type of rotor is shown in Figure 12-3. These
are used on high performance and competition vehicles.
They are not installed on most production automobiles
because they quickly wear out the brake pads.
Rotor Attachment
Rotors are attached to a wheel hub. The hub is
attached directly to the wheel spindle, knuckle, or axle
through wheel bearings, discussed in Chapter 16. For
proper braking ability, rotors must run true without any
scoring, lateral runout, or wobble. For this reason, the
rotor must be accurately attached to the hub. Most rotors
are separate from the hub, and are held in place by the lug
nuts and/or wheel studs when the tire and rim are installed,
Figure 12-4. Some rotors, especially those used in the front
of rear-wheel drive vehicles, are integral with the hub (the
hub and rotor are formed as one piece of cast iron). An
integral rotor is shown in Figure 12-5.
Splash Shield
To keep as much water and debris as possible away from
the rotor, most disc brake assemblies have a splash shield