It can hold the brake pad against the rotor disc and cause premature failure and if it gets hot enough from friction, start a fire.
Yes . Over time brake fluid can leak out and cause a failure.
Contaminated brake fluid.Rusted, rotted brake lines.
The most common cause is failure of the Master Cylinder. Leaking wheel cylinders & calibers is another cause. Of course worn brake pads or shoes can cause defective brakes. Lastly would be a broken brake line hose.
If the front brake caliper is sticking, the disc may be uneven. Brakes that are left to scrape on the disc for a long time before they are changed will damage the disc enough to cause sticking or slipping.
disc brake components
The rotor is the disc in the disc brake system.
If the front brake caliper is sticking, the disc may be uneven. Brakes that are left to scrape on the disc for a long time before they are changed will damage the disc enough to cause sticking or slipping.
With rear drum brake:-The brake drum may be out of round or may have a rust spot in it. -The brake drum may be cracked.With rear disc brake:-The brake disc may have extreme lateral runout or be mounted improperly. -The brake disc may be cracked. This would be dangerous-Combination of soft brake pads and a directional finish on the disc surface. A directional finish may go away with use and take the noise with it.Regardless of brake type:A brake disc or drum mounted to a bent hub flange or bent axle shaft can cause this noise.
worn thin
In case of cost..drum brake is better than disc brake.
Your brake pads may need replacing, the disc or drum may be warped or cracked, the caliper may need replacing, especially if there is metal on metal friction. Floating caliper (single piston) designs are subject to failure due to sticking which can occur due to dirt or corrosion if the vehicle is not operated regularly. This can cause the pad attached to the caliper to rub on the disc when the brake is released. This can reduce fuel effiency and cause excessive wear on the affected pad. Additional heat generated by the constantly rubbing pad can lead to warping of the disc also.