How do breaks squeak if/when they need to be replaced, but do not squeak when working normally.

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My breaks on my car started squeaking and I know that means I need to replace them. I’m just wondering how the mechanical system works.

In: Engineering

Most brake pads have a little piece of metal that rubs on the rotor to make the squealing noise while you still have a small amount of pad left. If your pads don’t have this, it’s the metal backing off the pad rubbing on the rotor.
If you live somewhere that sands the roads, you can get sand, or debris, between the odds and rotors that make the same noise.

There’s a little piece of metal that sticks up next to the pad called a chirper, and when the pad gets short enough for the chirper to touch the rotor it makes the squeaking.

If the brakes are continuously squeaking, the brake pads themselves might be completely worn out and do not have any remaining friction material. This causes the steel rotor to make contact with steel pad thus causing the squeaking sounds.

There’s something built into the break pad so that once you’ve worn through the good part of the pad it starts making noise… kind of like how on receipt paper in registers, you’ll see blue line when it gets near the end of the roll.

The material they make brakes out of today is specifically made not to squeak. They put a lot of money into research to make sure of that.

They also add a little metal clip that will make that squeak when your brakes are almost worn away. Without that, the first squeak would mean that you were clear through your brake pads, and you’d have trouble stopping. The clip should give you enough warning so you get them replaced before they can cause problems.