Most people are familiar with the telltale screech of a failing brake pad. In fact, this sound actually has very little to do with the pad itself. The familiar screeching noise produced by brake pads that are about to shuffle off this mortal coil is actually an intentional design feature. Once pads have worn down sufficiently far, a small piece of metal rubs against the rotor and produces that noise to tell you that it's time to do some maintenance.
Unfortunately, not all brake failures are kind enough to announce themselves so clearly. Instead, keep an eye out for these obvious symptoms that something has gone wrong in your vehicle's braking system.
A metallic grinding when you press on your brake pedal is a sure sign of trouble, although it can indicate any of a number of failures. If you've been ignoring squealing brake pads and that squeal has now been replaced by a worrying grind, however, then it likely means that your pads have been completely worn down and that your rotors are being damaged. Grinding when braking can also be the result of rotors that simply need to be replaced or foreign objects that have become lodged into your brakes.
Excessive Brake Dust on One Wheel
If you notice that one of your wheels is constantly dirtier than the others, then it's time to suspect a problem with your caliper. A stuck caliper will cause the pads on that wheel to constantly grind against the rotor, producing a significant amount of heat and brake dust. Additional symptoms of this problem include the car pulling in one direction, a grinding noise at low speed, and reduced braking power. A stuck caliper can potentially be a symptom of a bad brake line or other problem with the hydraulic system.
The (Wrong) Pedal to the Metal
Does your brake pedal feel soft or drop to the floor when you push it? If this happens, then it most likely means that there is an issue with the hydraulic system and you are losing brake fluid. This is an incredibly dangerous situation, so it is important to avoid driving your car until the leak can be fixed and repaired. These leaks often occur at the flexible brake lines near the calipers and so are usually fairly cheap and easy fixes. Rusted out brake hard lines can be a more expensive culprit.
A Pedal That Won't Get Down
On the opposite side of the spectrum, a brake pedal that is extremely difficult to push indicates an entirely different problem. Modern vehicles are equipped with brake boosters which make it easier to manipulate your car's hydraulic brake system using the pedal. If your brake pedal has suddenly gotten stiff and doesn't seem to know how to loosen up anymore, then most likely you have a brake booster problem. In some cases, this can also be the result of a vacuum leak. Assuming you can still apply enough force to stop the car, then this a somewhat less serious issue than the others on this list.
Regardless of which symptoms you are experiencing, however, brake problems should never be ignored. If you notice any change in your car's braking behavior, be sure to have it inspected by services such as Dualtone.