This is a basic guide to help point out tell-tale signs of potential brake problems often seen in Motor Sport.
It is important to remember that often problems with a disc rotor are the direct result of another component in the braking system or suspension that is no longer within its operating specifications. These problems can even be caused by poor fitment practices.
Heat Paint as a Diagnostic Tool
Themographic heat can be used to identify problems relating to brake callipers. If a calliper is functioning correctly the heat paint will change colour evenly as shown (fig. A) below. If the heat paint is changing colour more on one side than the other (fig. B) it indicates that the brake pad is dragging on that side. This can be caused by the calliper/rotor not fitted correctly, brake pad binding in the calliper, calliper piston(s) seized or even the calliper piston seals swollen or hard. If this is occurring it will reduce the life of the rotor and brake pads through overheating of the rotor and can even cause mechanical fracture of the rotor. To rectify this check the fitment of the calliper and brake pads first and if they are fitted correctly proceed with checking/overhauling the calliper.
Hub Mounting Face
It is very important to check the cleanliness of the hub mounting face when refitting or replacing the disc rotors. Over time the hub mounting face will develop a rust scale (fig. C) that must be removed before fitting a disc rotor (fig. D). This rust scale, if not removed, will cause the disc rotor to be mounted with excessive runout which will cause the rotor to wear unevenly resulting in DTV (Disc Thickness Variation). Brake shudder/pedal pulsation is the most common symptom of DTV. If a 2 piece style disc rotor is mounted with excessive runout it can result in mechanical fracture of the rotor at the hat mounting holes (fig. E).
Disc Brakes Australia.