Noisy brakes are probably one of the most common concerns that I’ve heard throughout my career. Customers complain, “My brakes squeak.” “My brakes grind.” “My brakes go (grinding noise here) when I try and stop.” And when people make that noise, it’s my absolute favorite.
For this issue’s article, we are going to be putting all new brakes on my Miata, but rather than just slapping a bunch of new parts on it, we’re going to go over how to do a proper brake inspection, some common causes for brake noise and some steps that may get overlooked.
As a professional technician, you know that when you push your foot on the brake pedal, you are pushing a piston. This piston pushes fluid through the brake hydraulic system. That force acts against the back of the caliper piston, causing the caliper to squeeze the brake pads into the brake rotor. This creates friction, the friction will slow down our wheel and then, of course, slow down our car.
There are times where a tiny bit of extra brake noise is totally normal. First thing in the morning when you hit those brakes, you’re actually cleaning a little bit of surface oxidation off the rotor. This is totally normal and can happen even with brand new brakes. The brakes on my Miata, however, are not totally normal, and this layer of oxidation needs to be addressed. See Photo 1.
Brake noise is typically broken down into three different categories, squealing, grinding and a clunk. While squealing can be a sign of a couple of different issues, the most common one is actually an indicator that the brakes may simply be worn out. Many brake pads have a small metal tab attached that functions as a wear indicator. When your brakes wear to a certain point, this tab, which I lovingly call a squealer, will actually make a little bit of contact with the rotor to alert the driver, the mechanic or sometimes everyone else nearby that the brakes are worn out and it’s time to replace them.
We can also have incorrect pad-to-rotor contact. The rust on this brake rotor is actually preventing the pad’s friction material to make good solid contact. When we push the brakes, rather than the pad contacting the rotor, it’s partially contacting rust. We can also get some squealing noise from things like overheating our brakes, the brake pad sticking to the rotor after we let off the brakes, damage to the shim, the backing plate or any of the hardware can cause our brake pad to stick onto the rotor. I’ve even seen brake pads installed backwards. It usually starts as a squeal and then they end up causing a grinding noise.
When it comes to grinding, this is typically much worse than a simple squeal and is often caused by metal-to-metal contact. The two most common faults are totally worn-out brakes and some kind of outside influence, most typically a rock that’s caught between the rotor and the backing plate. While this can scuff up the rotor a little bit, it’s typically not enough to warrant replacement. Sometimes it’s really easy to find the rock and get it loose, other times I’ve had to completely take apart the assembly in order to get it out.
When it comes to clunking, when we’re either pressinge or letting off of our brake, we’re going to inspect the brake assembly, but we need to also pay attention to other things that are in that corner of the vehicle. A pad not sitting in the brake caliper bracket properly, a piece of guide hardware that’s maybe damaged or fallen out, or the incorrect pad can all cause the brake pad to shift inside that caliper bracket. But we need to make sure we’re looking at the suspension and wheel bearings as well. A worn-out control arm bushing can cause the whole wheel assembly to shift, and that can make a very similar noise to a brake clunking noise.
No matter which one of these noise concerns we’re experiencing, we’ll do a visual inspection and a test drive. This first visual inspection is typically done with the wheels on, depending on what kind of wheel you have. If you don’t have big open spaces in your wheel, unfortunately, you’re going to have to take the wheel off to do the inspection. If that’s the case, I’d start with the test drive.
Here’s what I look for when I do my initial visual inspection. First, I’m going to look at the rotor to see how much rust is built up on the surface where the pad rides. As you can see on the Miata, there’s a lot of rust on there and that’s going to lead to poor brake performance. See Photo 2. I’m looking for obvious signs of metal-to-metal contact. This may show itself as a bright ring somewhere in the rotor. That may be due to a foreign object in the brake, or it may just be due to our brake pads being severely worn out.
I’m also looking to see how much friction material is left on the pads. It’s usually very easy to see the outboard pad and how much friction material is left. The inboard pad is a little bit trickier and you’re probably going to need a mirror in order to see the friction material. See Photo 3. On many caliper designs, the inside pad is what hits the rotor first. And so, a lot of times, that inner pad will wear a bit faster than the outer pad.
I’m also looking for anything loose or missing. This could be a little hard to tell. On this car for example, if the top guide was there and the bottom one wasn’t, that’s usually a sign that something fell out or wasn’t installed when the brakes were replaced. When looking at the rotor, we want to look at how much contact surface the pad is making to the rotor. If you can get behind the wheel, look at the caliper and the brake lines. We’re looking for things on the brake line like any bulging or cracking of the line. We’re looking for brake fluid leaks or obviously loose hardware on the caliper.
For the rear, slide underneath the car with a flashlight and take a look at the parking brake cables, make sure that the outside sheeting is not all bunched up. We can usually test the parking brake pretty easily just by using it and seeing if it holds the car. Now, if you have drum brakes, you’re going to be pretty limited on what you can actually inspect without taking it apart.
On our brake inspection test drive, I’m checking for three things. I’m listening for noise, I’m feeling for vibration and I’m feeling for whether the vehicle pulls either when I press the brake or when I let off the brake. I do this with three levels of brake application — light brake (think 10% or so of pressing the brake pedal), moderate brake pedal pressure (40-60% or just normal braking) and then full-on, all the brakes you can get. Of course, before you do that one, make sure you’re being safe.
Certain noises and vibrations can present themselves at different pedal pressure. When we’re doing these three levels of braking, we want to make sure we’re listening. Is it coming from the front? Is it coming from the rear? A lot of times the front brakes are going to make more noise or have more of an issue under heavy braking. When it comes to vibration, we’re going to do the same thing. When we press the brakes and feel the steering wheel vibrating, that typically means that we have an issue with the front rotors.
Oftentimes we refer to that as having a warped rotor, but that’s not technically accurate. The more accurate way to call it is excessive lateral runout. All this really means is we have high spots and low spots in the rotor causing that vibration. With the rest of the car or you’ll really feel it in the seat, it’s usually the rear rotors that are the issue. It’s important to remember too, that there are other things that can cause a vibration. Tires, an axle, incorrect torque on a wheel, even a bad wheel bearing can cause some of these similar kinds of things. I swear, the newer cars get, the weirder wheel bearing failure is.
When it comes to pulling, we need to pay special attention. If we hit the brakes and the car juts to the side, we have a problem. If when we let off the brake, the car does the same thing, we have a problem. We have maybe a pad that’s not connecting to the rotor at all, or a pad that’s sticking, causing the car to pull. We want to make sure we make note of all these things so that when we do our inspection with the car up in the air, we’re paying extra close attention to that kind of stuff.
Finally, on the test drive, as you drive more and do more aggressive braking, if the noise starts to go away, it might just be something as simple as brake dust buildup. Once those brakes cool down, if you clean them off, your noise is taken care of.
On our in-depth inspection before we take our wheels off, I like to rotate them by hand and listen for any noise. This may help us isolate which corner of the vehicle is having the problem.
Once I remove the wheel, I’ll inspect the surface where it mates to the rotor as well as inspect the rotor where it mates to the wheel. Surface rust or debris can be a source of a vibration. With the wheel off, do a quick visual inspection. Make sure you don’t have any foreign materials like rocks or any metal-to-metal contact like the backing plate hitting the rotor, which is another common cause of brake noise.
Next, remove the caliper and inspect it. Then inspect the caliper piston for rust and damage. Also inspect the boot around the piston. Make sure there aren’t any rips and that brake fluid isn’t leaking from the seal behind it. Inspect the housing of the caliper to make sure there’s no damage or there aren’t any brake fluid leaks. Also inspect the slide pins for any scoring or wear. Make sure they’re not bent. A straightedge is an amazing tool for that job. Take a look at the dust boots for the slide pins. It should take a fair amount of force to get them to pop off either the slide pin or the caliper. If you find anything that you’re not 100% confident in, replace it. There is no need to try to salvage parts that may not be worth it.
Next, let’s remove the pads. Look for uneven pad wear. A little bit of difference in pad wear is not that big of a deal, but if, on the top section of the pad, we had 8 mm of pad and the bottom we had 2 mm of pad, that would be an issue. If the outward pad is pretty even at 8 mm and the inboard pad is metal to metal, we may have a caliber or caliper carrier bracket issue.
Check the backing plate’s condition. My backing plate slid down to the bottom of the pad. This could be a source of noise. This could also cause the brake pad not to fully seat in the rotor. It also looks like the guide hardware was actually hitting the backing plate or the shim plate on the brake pad. Those could cause our brake pad to hang and cause some uneven wear.
Inspect the pad where it rides on the guide hardware. This is where I noticed that the backing plate was actually shoved into the hardware. It’s recommended that these parts be replaced. Next, let’s inspect the brake caliper carrier. These typically have a lot of brake dust buildup on them. So, when we go back together, cleaning is going to be vital. Look for rust buildup or any damage to the metal. Check the condition of the hardware to be sure that it was installed properly. Also check the surface where the pad rides. This pad rides on clips on the caliper carrier bracket. So, the inspection of the hardware is very important. Not all cars have these shims or this hardware with them. They ride directly on the caliper bracket. Make sure that there isn’t any metal damage. What I’ve seen happen is the metal actually gets pushed up where the pad rides and it can prevent the pad from fully seating into the brake rotor. Also look at where the brake caliper bracket mounts. Make sure there’s no rust or damage and the threads in the hub are good.
Now we have full view and we can do a good inspection on our rotor. We’re looking for any glazing and overheating. Overheating kind of looks cool because it will turn the rotor blue. We’re also looking for rust. When we remove the rotor, we want to do these same checks on the backside. Be sure there was no metal-to-metal contact and inspect for rust on that side.
Inspect where the rotor mounts to the wheel hub. These two surfaces really do need to be cleaned. While I’m not going to clean this old rotor, we are going to clean this wheel hub surface. If you are chasing a brake vibration or you wanted to determine whether your vibration was caused by the rotor having excessive lateral runout or perhaps a wheel bearing issue, we can break out the dial indicator and measure the rotor runout. See Photo 4. This’ll measure high spots and low spots in the brake rotor and can help us identify the source of a vibration. Sometimes doing it just on the rotor is enough. If you’re trying to chase a wheel bearing, you may need to take the rotor off and measure that runout on the bearing.
Commonly Overlooked Steps
As we go back together with our new brakes, let’s talk about some of the commonly overlooked steps on brake jobs. The first one is cleaning everything. A clean brake job is a happy brake job. Make sure to clean the wheel hub where the rotor mounts and the caliper. If there was anti-squeal on the brake caliper, either on the piston or the other side, make sure you clean that.
Next clean the caliper carrier. We need a good clean surface for our hardware to reinstall on. I love media blasting these, but a wire wheel or wire brush works well too. Even though these rotors are brand new, we need to clean them. A lot of times, rotors come with a coating on them to prevent them from rusting while they’re in the packaging. A little bit of brake clean on a rag works really well or soap and water work good too.
Another thing that’s often overlooked is replacing the hardware. Installing new pads and new rotors but using the same old guide clips is a bad choice. They can become worn or deformed over time. This also applies to any bolts that you might remove that are one-time use only. And any of those bolts that you take off, you want to make sure that you torque them down properly. Also, make sure that if any of this hardware requires either threadlocker, lubricant or anti-seize that you’re putting it on in the right place. This is where referring to the repair manual is a wonderful idea.
None of our hardware required any threadlocker, but it did require lubricant on the caliper piston where it hits the brake pad, on the opposite side of the caliper where it hits the brake pad and a small amount where the pad rides on our clips. You don’t need to coat the entire back of the brake pad; a little bit goes a long way. And, of course, when we put our slide pins back in, we want to make sure that we clean and lubricate those as well.
Another thing I see overlooked often is brake fluid service. Brake fluid is a vital part of maintenance on your brakes. Brake fluid is hygroscopic, which means that it attracts and holds water. This is a good thing because then we don’t just have straight water settling and rusting our brake lines. But that moisture does build up in the fluid over time and can impact how the brake fluid perform. Most manufacturers recommend every two years.
The step I see skipped the most is bedding in your brake pads. To get the most out of your new brakes, you’ve got to make sure you bed them in properly. This is sort of like a break-in period for your new brakes. Depending on what kind of brakes you install in the car will depend on what this process looks like. Be sure to refer to the brake pad manufacturer for their exact bed-in procedure. It typically involves a gradual buildup of heat in the pad and in the rotor. Do a couple of low speed stops, let them cool for a second, moderate speed stops and then higher speed stops. This puts a very thin layer on the rotor called a transfer film. We want to have that layer nice and even for the best possible brake performance.
Failure to bed in your brakes can lead to noise and vibration. There’s nothing worse than spending all this time and energy putting new brakes on just to have brake noise right away afterward. It’s important to note too that some brake pads can actually take up to 400 miles or so to fully develop that film. And, of course, if you’re doing this on the street, be extra careful.
Now, there’s one final thing I have to say, because it wouldn’t be a brake article without talking about this, and that is always, always, always pump the brake. I’m at the point now where anytime I get into a car, no matter what, I pump the brake pedal. Thankfully, this is a pretty rarely overlooked thing, but I have seen no less than three times in a professional shop where the brakes weren’t pumped to fully seat the caliper and pad into the rotor and it caused issues. Twice I saw toolboxes smashed. Thankfully, no one was hurt. However, once I did see someone get hurt. Luckily they were OK, but for real, this is something you want to make sure that you do every time.