Brakes are incredible devices. They’re able to bring even a hulking SUV to a stop in a matter of seconds. Vehicle brakes are normally reliable and quiet, and noise can indicate a problem. Serious issues make serious noise, leaving you asking “why are my brakes grinding?” If your brakes are making noticeable noise, here’s what you need to know.
How do brakes work?
Modern brake systems work by applying friction to moving parts, which converts the vehicle’s kinetic energy from movement into thermal energy. The brake pedal is actually a lever that increases pressure inside the brake master cylinder. Since brake fluid is not easily compressed, it flows under pressure to the calipers where a piston presses the brake pads into contact with the brake rotor. This contact creates friction, released as heat, and the vehicle slows to a stop.
Noise usually only happens as the brake pads wear out. Brake manufacturers add a little metal piece to the brake pads near the wear surface. As brake use wears down the brake-pad friction material, the metal wear indicator hits the metal rotor, producing an audible shriek. It’s annoying but it just means that it’s time to change the brake pads, and probably the rotors as well. But when it comes to brakes, grinding is not the same as squealing. Here’s what to look for.
Why are my brakes grinding?
Grinding brakes are often a warning sign of a larger brake-system issue. It could be caused by any of the following problems.
Worn brake pads
The above-mentioned wear indicator makes a squealing noise when your pads are worn out, but what if you ignore it? Aside from irritating everyone around you in traffic, eventually you’ll grind away all of the brake-pad friction material. That leaves only the backing plate which causes a grinding sound. It can also result in noticeably reduced braking performance. It’s as unsafe as it is unpleasant.
Rusty caliper bolts
There’s more to the brake system than just pads and rotors. The caliper has pistons, shims and bolts that all need lubrication. The caliper bolts are also called guide pins because they guide the pad into the proper angle for contact with the rotor. If the guide pins get rusty, they’ll get stuck, and the incorrect angle of the brake pad creates a dragging feel and grinding noise.
If you change your brake pads but leave the rotors in place year after year, you probably have bad rotors. Using the brake system wears out both the brake pads and rotors, slowly removing metal from the disc surface. Get the brakes too hot in their compromised state and the rotors will warp, leading to a scraping, grinding sound.
Debris in the caliper
There’s a small space between the pad and rotor, usually small enough to be measured in fractions of a millimeter. If anything tiny gets stuck in there, such as sand or dirt, it’s going to make a constant grinding noise as it rubs on the rotor surface. If you recently took your vehicle off-road and noticed the brakes grinding, power washing may be enough to remove the debris. If that doesn’t work, the next step is disassembling the caliper for a better look.
Car sits for too long
Rust. It’s the enemy of anything metal, including car parts. Brake rotors are most commonly made of cast iron. Leave your car out in the rain overnight and you’ll see specks of iron oxide on your brake rotors. When you first head out to work, you’ll notice a loud grinding sound, even when not pressing the brake pedal. That’s the minor surface rust getting scrubbed off by the brake pad, and it goes away after using the brakes a few times.
But if your car sits too long without being driven, that’s another story. If the rust penetrates below the rotors’ surface, no amount of driving will correct it. You’ll need new rotors.
Poor quality pads
Maybe you tried to save a few bucks by buying the economy brake pads instead of the usual standard replacement parts. Unfortunately, cheap pads are constructed of cheap materials, including excess metals, which create more noise. When that metal gets rusty, look out for even more noise. Next time, shop around and get the best brake pads that fit your budget.
Bad wheel bearing
A grinding noise coming from a bad wheel bearing could easily be confused for a brake issue. Here’s one way to narrow it down: If the grinding noise gets louder as you accelerate, then it’s likely a wheel bearing and not a brake issue. If the noise increases as you use the brakes, then the braking system is the more likely culprit.
Glazed brake pads
Brake parts are designed to get hot. But even quality pads can overheat in the right circumstance. If you’re riding the brakes while towing, going down a mountain grade or out on a high-speed track, your brakes can get overheated and glazed. This hard, shiny glaze prevents the pad and rotor from connecting and reduces your ability to stop. It makes a grinding noise too. Rather than try to remove the glazing, the best bet is to swap your overheated brake pads for new ones.
Why are my brakes grinding after new pads and rotors?
This one is frustrating. You notice your brakes grinding, then go through all the time, effort and expense to replace your brake pads and rotors. But on your first drive, your brakes are grinding all the same. If new pads and rotors are what caused the grinding, or don’t resolve the previous grinding issue, one of a few things is likely happening.
First, there is a protective coating on the rotor and pad surfaces that prevents them from rusting on the store shelf. Scrubbing off that coating makes a sound, but it quickly disappears after a couple of drives. Second, if you only replace the pads, they are “bedding in” to the slight groves and tracks left by the previous pads. Again, go drive for a bit and you’ll be fine.
Finally, if your brakes are still grinding with new pads and rotors, you might have misaligned something small like a pad shim. It could be in very slight contact with the rotor, creating a grinding sound as you drive. This will also go away on its own once the component wears down a bit, but that’s not the best way to address it. Remove the wheel to take a closer look, or hand the job off to a professional.
What to do if your brakes are grinding
Grinding usually requires new parts. But if sound is the only problem and your brakes are otherwise performing well, you may not need to spend money just yet.
If the pads are brand-new, give them a couple of drives to quiet down. If you recently drove through deep sand or mud, go to a self-serve car wash and blast some water at the brakes to attempt a cleanout. Figure out the last time you had the brake pads and rotors changed. If it’s been several years and even more miles, you’re probably due for a new set.
Note that you must replace left and right sides at the same time, although it is possible to swap out just the front or rear pads as needed. If you notice any decrease in stopping power, get your brakes checked out and repaired immediately.
Frequently Asked Questions
Is it safe to drive with grinding brakes?
If you don’t know what's causing it, assume the worst. If your braking performance hasn't changed, it's probably safe to drive either home or to a shop to take a closer look. While it could be something minor, it’s best to get this checked out by a professional as soon as possible.
How often should you replace brake pads?
For any routine replacement parts, always refer to your owner’s manual, or your local service center. In general, brake pads should last between 25,000 and 65,000 miles.
How long does it take to get new brake pads?
Replacing brake pads is a fairly simple task, and usually takes a pro mechanic 30 minutes to an hour. The DIY route takes a little longer if you’ve never done it before; expect an hour, minimum.