Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairEasy
A technician is performing a pre-purchase inspection on a used vehicle. They observe that the front brake rotors have a slight blue discoloration near the outer edge and small, localized hard spots (glazing) on the friction surface. The current brake pads are ceramic. What do these observations MOST likely indicate?
- AInsufficient brake fluid circulation.
- BNormal wear for ceramic pads.
- CThe vehicle has been subjected to harsh or aggressive braking.
- DExcessive rotor runout.
Show answer & explanationAnswer & explanation
Correct answer: C. The vehicle has been subjected to harsh or aggressive braking.
Blue discoloration and localized hard spots (glazing) on brake rotors are classic signs of excessive heat. This typically occurs when a vehicle is subjected to harsh or aggressive braking, such as repeated hard stops, driving in mountainous terrain, or towing heavy loads, which can overheat the rotors.
Why the other options are wrong
- A. Insufficient brake fluid circulation would primarily cause issues like a soft pedal or dragging brakes, not specific rotor discoloration and glazing.
- B. While ceramic pads can handle high temperatures, blue discoloration and glazing are not normal wear but indicators of overheating.
- D. Excessive rotor runout causes pulsation, not typically blue discoloration or glazing unless it leads to severe localized heat, but aggressive braking is a more direct cause.
Rotor Overheating Signs
Visible signs of brake rotor overheating include blue or purple discoloration (heat spotting) and localized hard spots (glazing) on the friction surface, often indicating aggressive braking or system issues.
- Blue/purple color indicates high heat.
- Glazing is hardened, friction-reduced material.
- Reduces braking effectiveness and can cause noise.
Memory trick: Blue means hot, glaze means stress, brake hard, you'll make a mess.