Brake squeaks and squeals most commonly occur from heat and vibration. The caliper, pad and rotor assembly are secured to the vehicle, but the weight of the vehicle and the demand of the braking power create stress on the moving parts in the braking system. The friction material of the pad or shoe contacts the smooth surface of the rotor or drum which creates heat. There are many other variables that can cause front or rear brake noise.
Disc Brake Squeaks
Disc brakes operate by calipers that hug two pads on both sides of the vertically positioned disc. The disc rotates with the velocity of the wheel when driving. To slow the vehicle down, hydraulic pressure expands a piston inside the caliper upon demand, which squeezes the pads against the rotor. Friction material of the pad is usually constructed of metal and brass flakes. This composition can often be the culprit of front brake noise.
Front brakes accommodate 75 to 80 percent of the braking capacity for vehicles. They work harder than rear brakes, and that creates a more hostile environment for the braking system.
Lubricants intended for allowing free movement to the components in the front braking systems can erode away from exposure or regular wear and tear.
Common disc brake squeaks are most usually caused by cracked or worn pads, compromised rotor/disc surface, dry or corroded slides, brake pad drag or slipped shims. Wear sensors applied to the backing plate of the pads will also pronounce a squeal or squeak. These sensors inform the driver that the pads are low and in need of attention. Although a simple metal tab on most applications, these sensors can vary in scenarios when they sing. On some vehicles, the tabs will scrape along the surface of the rotor, making noise until the brakes are applied, and then go away until the brakes are released. Other applications make noise when the brakes are applied only.
Lubricating all moving components, replacing rattle clips, making sure Teflon coated shims are in place and the pads are seated in their mounts properly will usually eliminate noisy disc brakes.
Drum Brake Squeaks
Drum brakes work inside a closed environment, unlike disc brakes. In most cases, the drums entrap brake dust formed when the friction material slowly wears away from the shoes. The dust accumulates and then gets trapped between the surface of the shoes and the drums. Removing the drums and cleaning out the brake dust helps--until the dust builds up again.
Applying lubricant under the shoe tabs that contact the backing plate of the drum brakes will also prevent squeaks. The backing plate is made of thin metal and the tabs of the shoes are made of hardened steel. These two surfaces rub together when the shoes reposition under demand.
Worn springs or other hardware can comprise the rear drum brake systems and contribute to rear brake noise.
Seeping or leaking rear wheel cylinders or blown axle seals can contaminate the rear drum brakes. Although a full shoe and hardware replacement is needed in addition to replacing the cylinder and/or seal, this scenario is more rare. The lubrication from the brake fluid or axle fluid helps prevent noise. However, this makes the other wheels work harder when braking, and can cause premature wear and duress.