In normal circumstances, the car brake rotors (discs) should be of silver color or gray. However, under some conditions, they can turn blue. This is a sign that there’s something wrong with your brakes, and it’s highly advised that you take action as soon as possible.
How this system works:
Pressurized brake fluid is sent through the lines from the master cylinder. In the caliper, the fluid actuates a piston, which effectively closes the caliper. This pinches the brake rotor between the inner and outer brake pads.
The harder you press the brake pedal, the harder the caliper pinches/squeezes the rotor. In a car equipped with antilock brakes, the ABS system keeps them from locking up by pulsating the brakes dozens of time per second.
The squeezing action of the caliper and pads against the rotor creates friction and heat. Friction is a necessary component here–it’s what slows and stops your car. Heat is unavoidable, but excessive temperatures can actually cause damage. This is where bluing can occur. If one of your rotors has turned blue, it’s important to have the problem diagnosed, as it’s an indication that something’s wrong. Over time, it could even lead to cracking of the rotor and damage to the pads, as well as compromising your safety on the road.
Common reasons for this to happen:
- Locked Caliper: One very common reason for rotors to turn blue is that the caliper is locked and the brake pads remain in almost constant contact with the metal. This might be slight enough that you don’t notice any drag during normal operation, but it will be enough to generate significant heat and wear.
- Corroded Slide Pins: Your car’s calipers slide back and forth on metal pins. These pins need to be well lubricated, clean and free of debris. If they become corroded, the caliper will not slide in and out properly and can remain too close to the rotor rather than moving back to the start position.
- Pinched/Deteriorating Brake Line: Your brakes work on hydraulic pressure. If there’s damage to one of the brake lines (an internal damage to the liner that limits the amount of fluid flowing in and out), it can cause your caliper to stay at least slightly engaged at all times. This generates heat and blues your rotor.
- Driver Error: If you’re a “two-footed” driver or regularly ride your brakes because you do a lot of stop and go driving or live in an area with lots of hills, you could be the inadvertent cause of the problem. Constantly engaging your brakes causes the same buildup of heat as having a locked caliper, but you’ll notice bluing on two or four rotors, rather than just one.
How important is this service?
Having brake rotors that turn blue can become an expensive problem, and it can also reduce your safety on the road. Extreme heat can cause your rotors to warp and even crack, and your brake pads will deteriorate rapidly, leaving you with less stopping power. If the problem affects both front brakes, you may also notice brake fade. It is recommended that you have the vehicle inspected and the problem corrected at the earliest.