Maintaining cars requires regular maintenance, and part of that maintenance is getting new brakes occasionally. If you’ve recently put on new brakes, you might have noticed an unpleasant smell – and maybe even glimpsed some smoke.
Do new brakes smell and smoke? It is perfectly normal for new brakes to smell and smoke. The smell and smoke are actually so common it has a name: polymerization. This is basically a curing process that is breaking in your new brakes. The smoke and smell are a result of the gases formed during the curing process.
Now that you know it’s not a big deal if your new brakes smell and smoke, let’s take a deeper look at exactly what causes brakes to smell and smoke.
Is it Normal to Smell Burning After Changing Brakes?
A burning smell after changing brakes can be a bit worrisome if you don’t realize it’s part of the normal process of breaking-in new brakes. Whether you put the brakes on or a mechanic did, you’re likely to smell some burning and/or see some smoke. As mentioned above, it’s called polymerization.
What is Polymerization?
Polymerization is a rather big word with a fairly basic definition. It’s a curing process that happens the first few times you use the brakes. It happens when the brake pads move against the rotors. This causes friction, which generates a lot of heat. When the brake pads touch the rotors, the curing happens.
This curing causes gases to form, which generates the smell and smoke you’re probably seeing out your rearview mirror. You might be wondering why the manufacturers don’t just cure the brakes before installation to avoid the smell and smoke.
Actually, some mechanics do start the curing process before the brake pads are sold. In these cases, the manufacturer “scorches” the brake pads.
The brake pads are put under extreme heat and pressure for a brief time to force a layer of friction on the first 1 to 2 mm of the brake. When manufacturers do this, you’ll spend less time breaking in your new pads.
The reason not all manufacturers cure the brakes first is that it’s best for the brake pads to be broken in by the rotors that will be on the intended vehicle. Doing this accomplishes the following:
- Improves pedal feel
- Reduces brakes squealing
- Reduces brake dust
- Lengthens the life of your pads and rotors
This curing is all accomplished through the process of bedding-in or burnishing your brakes. This basically means braking in your brakes. Let’s take a look at this process.
Bedding-in Brakes
As mentioned above, some manufacturers do cure brake pads before installation. In these cases, bedding-in is not required. In most cases, though, you’ll need to bed-in or break in your brakes.
Bedding-in your brakes does the following:
- Cures the friction material on the brakes
- Spreads out an even layer of material from the brake pad onto the rotor (transfer layer)
- Smoothes the surface of the rotor
There are a number of brake pads out there and most require a bedding-in process specific to that manufacturer. You can always find this information in the manufacturer’s materials.
It’s very important to follow the directions as precisely as possible because this ensures the transfer layer is even. If the layer isn’t even, you may see the following problems:
- Vibration in the steering wheel or brake pedal
- Compromised brake performance
- Discomfort while driving
Step-by-Step: How to Bed In Brakes
Bedding-in your brakes requires quite a bit of accelerating and quick decelerating. It’s best to do this early in the morning in an area without a lot of traffic so you can complete the steps as directed. Remember, follow your manufacturer’s directions but here’s a look at what the bedding-in process may look like:
- Accelerate to 60 miles per hour (MPH) and tap the brakes a few times. This brings your brakes up to their normal operating temperature and prepares the pads and rotors for the high heat you’ll generate in the following steps.
- Push the brakes down firmly to decelerate from 60 MPH to 10 MPH. Remember, you’re not stopping completely, but you need to press the brakes fairly firmly but not enough to engage the ABS or wheels lock mechanism.
- Speed back up to 60 MPH once you reach 10 MPH and apply the brakes again back down to 10.
- Repeat this cycle 8-10 times without ever stopping completely. Stopping completely will lead to excessive brake pad material on the rotors and ruin the performance of your brakes.
- After your final cycle, accelerate and drive around for a bit, using your brakes as little as possible, so they cool down.
If you’ve successfully bedded-in your brakes, you should see a light gray film and slight blue tint on your rotor. The film is the brake material transferred onto the rotor. The blue tint is a sign that the rotor reached an appropriate break-in temperature.
If you put on new brake pads but still have old rotors, you may need to complete a second bed-in cycle. It’s important to let the brakes cool down first before completing a second cycle.
Other Causes of Smell and Smoke With New Brakes
There are a few other issues that may cause your new brakes to smell or smoke. Here are a couple of other possibilities:
- New rotors coated with rust inhibitor
- Stuck caliper
- Riding the brakes
Let’s take a look at each of these issues to identify which one could be a cause of your smell and smoke.
New Rotors Coated With Rust Inhibitor
New rotors are generally coated with a rust inhibitor, so if you installed new pads and rotors, this could be the problem. The rust inhibitor burns off the first few times you use the brakes. This can cause smoke, which also might smell.
The easiest way to avoid this issue is to wash your new rotors with soap and water before you install them to remove the coating. You can also just use brake cleaner to remove the coating.
Stuck Caliper
A stuck caliper could be the cause of your brakes smoking. This generally only happens with older brakes but is worth looking at in the rare case it may be the cause.
Let me start by explaining what a caliper does. Assuming your car has disc brakes, your rotors are attached to your car’s wheels. A caliper pushes against the rotor and causes friction, which slows the wheel down.
Dirt or corrosion can cause a caliper to stick. A stuck caliper will cause your brake pad to overheat severely, causing smoke.
A good sign that you have a stuck caliper (besides smoke) is if one side of your brakes is worn far more than the other side. You can also take the wheel off and have someone apply the brake while you watch the brake pad. If the pad doesn’t retract from the rotor, you likely have a stuck caliper.
Riding the Brakes
Whether your brakes are old or new, riding the brakes can cause a burnt smell. Perhaps you were driving down a very steep hill and kept your foot on the brake for much of the time. The friction building during this process will generate a burnt smell.
If this happens, you’ll want to cool your brakes down as quickly as possible because you can damage your brakes if they continue to heat in the same spot on the rotor.
To cool down your brakes, try to drive or coast for at least five minutes without using your brakes. Of course, this isn’t always possible if there’s traffic around so you’ll just have to do your best. Obviously, brakes are one of the most important components of your vehicle. You certainly would not want to go without them, so if none of the above possibilities seem to be the cause of smell and smoke with your new brakes, you need to get them checked out. It’s certainly better to spend a little money and cruise along the road safely.