Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairEasy
During a brake inspection, a technician notices that the driver's side front brake rotor has a distinct blue tint and several hard spots, while the passenger's side rotor appears normal. What does the blue discoloration and hard spots on the driver's side rotor indicate?
- ANormal wear and tear for a high-performance brake system.
- BIncorrect brake pad material used on that side.
- CContamination from an oil or grease leak.
- DExcessive localized heat, likely from a dragging brake.
Show answer & explanationAnswer & explanation
Correct answer: D. Excessive localized heat, likely from a dragging brake.
Blue discoloration and hard spots (often called 'hot spots') on a brake rotor are clear indicators of excessive localized heat. This is most commonly caused by a dragging brake, where the pads remain in constant contact with the rotor, generating extreme friction and heat.
Why the other options are wrong
- A. While high-performance brakes can run hot, blue discoloration and hard spots indicate overheating beyond normal operating conditions.
- B. Incorrect pad material might affect braking performance or wear rate, but it wouldn't inherently cause localized blue discoloration and hard spots on the rotor unless it led to extreme, consistent dragging.
- C. Oil or grease contamination typically results in a spongy pedal, reduced braking, and a specific odor, not blue discoloration and hard spots.
Rotor Discoloration
Blue discoloration and hard spots on a brake rotor indicate excessive heat, usually from a dragging brake or severe overheating. This can lead to rotor warpage and reduced braking efficiency.
- Caused by temperatures exceeding rotor's design limits.
- Hard spots are areas of martensite, making rotor brittle.
- Leads to pulsation and reduced friction.
Memory trick: Blue means hot, hard spots mean a lot, of heat that the rotor got!