17/05/2004
When you've just had new brake pads or rotors fitted to your vehicle, it's not uncommon to notice a faint wisp of smoke during the initial period of use. This phenomenon often leads to a common question among drivers: "Do rotor pads smoke?" The short answer is, yes, under specific circumstances, they absolutely can, and it's often a sign that a crucial process known as 'bedding in' is taking place. Understanding why this happens, and when it's a normal part of vehicle maintenance versus a red flag, is vital for every responsible car owner.
The act of bedding in new brake pads and especially new rotors is a critical step in optimising your braking system's performance and longevity. It's during this process that the components are subjected to controlled heat cycles, allowing them to properly mate and prepare for effective everyday use. While the sight of smoke might initially cause concern, it's typically a harmless and expected part of this essential procedure.
Understanding Brake Bedding In: Why It's Crucial
Bedding in, sometimes referred to as 'burnishing,' is the process of gently transferring a thin, even layer of friction material from the brake pad onto the rotor surface. This creates a compatible interface between the two components, optimising their performance and ensuring consistent, reliable braking. Without proper bedding in, your new brakes may exhibit reduced stopping power, increased noise, and premature wear. It's not merely about 'wearing in' the parts; it's about a microscopic bonding process that sets the foundation for your braking system's future efficacy.
During manufacturing, brake pads are typically held together with resins and other binding agents. When these new pads are first used and heated up, these compounds can vaporise or burn off. This is the primary reason for the initial smoke you might observe. The process also helps to degas the pad material and ensure that the entire surface of the pad makes full contact with the rotor. For new rotors, bedding in helps to remove any protective coatings or manufacturing oils and prepares the metal surface for optimal friction material transfer.
The Science Behind the Smoke
The smoke you see during bedding in is usually a combination of several things: the burning off of manufacturing lubricants, volatile organic compounds (VOCs) and resins used in the pad's bonding process, and sometimes even the very fine dust of the friction material itself. As the brakes heat up during the bedding cycles, these substances are released as gas or smoke. It's a temporary phenomenon, and once the bedding-in process is complete, this type of smoke should cease.
The Proper Bedding-In Procedure
The method for bedding in new pads and rotors is quite specific to ensure the best results. As a general guide, and noting that specific instructions can vary slightly between manufacturers (for instance, Bendix General CT pads are designed not to require bedding in), a common and effective procedure involves a series of controlled stops:
Initial Warm-Up: Begin by driving gently for a few miles to bring the brakes up to operating temperature. Avoid any hard braking during this initial phase.
Controlled Stops: Find a safe, straight road with no traffic. Accelerate your car up to approximately 80 km/h (about 50 mph). Then, apply the brakes firmly and consistently, but avoid locking up the wheels, until you come to a near-complete stop, or at least significantly reduce your speed to around 10-15 km/h. Do not come to a complete stop if possible, as this can imprint the pad material unevenly on the hot rotor.
Repeat the Process: Immediately accelerate back up to 80 km/h and repeat the firm braking manoeuvre. You should repeat this process several times – typically between 6 to 10 cycles, depending on the manufacturer's recommendations. Yes, during these repetitions, you will likely notice a bit of smoke emanating from the brake area. This is normal and expected.
Cool-Down Period: After completing your series of stops, drive for a few miles at a moderate speed without heavy braking. This allows the brakes to cool down gradually, preventing warping and ensuring the transferred material fully cures onto the rotor. Avoid coming to a complete stop and holding the brake pedal down while the brakes are still hot, as this can leave a pad impression on the rotor, leading to vibration or judder later on.
Gentle Use: For the next 100-200 miles, try to avoid any extremely hard braking situations. This gives the pads and rotors a chance to fully settle and achieve their optimal performance.
It's crucial to follow these steps carefully. Skipping or improperly performing the bedding-in process can lead to issues like reduced braking performance, noise (squealing or grinding), and premature wear of your new components. Remember, while a bit of smoke is normal during this process, excessive smoke or a strong burning smell that persists beyond the initial bedding in period is usually a sign of a problem.
The Exception: Bendix General CT Pads
It's important to note that not all brake pads require the same bedding-in procedure. As mentioned, some manufacturers, like Bendix with their General CT pads, design their products to be 'ready to go' right out of the box, requiring no special bedding-in. This is typically achieved through advanced friction materials and manufacturing processes that pre-condition the pads. Always check the specific instructions provided by your brake pad manufacturer, as following their guidelines is paramount for safety and performance.
When Is Brake Smoke Normal vs. A Cause for Concern?
Distinguishing between normal bedding-in smoke and problematic smoke is key to maintaining your vehicle's safety.
Normal Brake Smoke:
During Initial Bedding In: As described, light smoke during the first few hard stops with new pads or rotors is normal. It's the binders and resins burning off, and it should subside quickly after the bedding-in process is complete.
After Extremely Hard Braking (e.g., Track Use): While less common for everyday driving, if you subject your brakes to extreme, sustained heat (like during a track day or spirited driving down a long, steep hill), you might see a brief wisp of smoke. This is due to the pads exceeding their normal operating temperature range and is a sign of extreme stress on the system. For regular road use, this shouldn't occur.
Abnormal Brake Smoke (Cause for Concern):
If you observe smoke from your brakes at any other time, especially if it's accompanied by a strong, acrid burning smell, it's a clear indicator of a problem that needs immediate attention. Here are common scenarios and their potential causes:
Continuous Smoking After Bedding In: If your brakes continue to smoke long after the initial bedding-in period, or if they smoke during normal, light braking, something is wrong.
Smoking from Only One Wheel: This is a strong indicator of a localised issue, such as a sticking caliper on that specific wheel. A sticking caliper means the brake pad remains partially engaged, causing constant friction and heat build-up, even when you're not applying the brakes.
Associated with Other Symptoms: If the smoke is combined with a pull to one side when braking, a spongy pedal, grinding noises, a lack of braking power, or excessive heat radiating from a wheel, do not ignore it.
Common Causes of Abnormal Brake Smoke:
Sticking Caliper: This is one of the most frequent causes. A caliper piston or slide pins can seize due to corrosion or lack of lubrication, preventing the brake pads from fully retracting after you release the pedal. This leads to constant friction, excessive heat, and smoke.
Seized Brake Piston: Similar to a sticking caliper, the piston within the caliper can seize, keeping the pads pressed against the rotor.
Worn-Out Brake Pads/Rotors: If your pads are completely worn down, the metal backing plate can grind against the rotor, generating extreme heat and producing smoke. Similarly, severely worn or warped rotors can cause excessive friction.
Contaminated Brake Pads: Oil, grease, or brake fluid leaking onto the brake pads can cause them to smoke and lose effectiveness. These contaminants burn off when heated, creating smoke and a foul odour.
Incorrect Installation: If brake components were installed improperly, such as a caliper not being seated correctly or a pad being installed backwards, it can lead to uneven wear, excessive friction, and smoke.
Overheated Brakes: While less common for everyday driving, prolonged heavy braking, such as descending a very long, steep hill without downshifting, can overheat the brakes to a point where the pads begin to smoke and fade (lose effectiveness). This is dangerous and can lead to brake failure.
Troubleshooting and Safety Precautions
If you encounter abnormal brake smoke, it's crucial to act swiftly and safely:
Pull Over Safely: Find a safe place to pull your vehicle over as soon as possible. Do not continue driving with smoking brakes.
Allow to Cool: Let the brakes cool down naturally. Do not pour water on hot brakes, as this can cause thermal shock and warp the rotors.
Visual Inspection: Once cool, visually inspect the smoking wheel. Look for obvious signs like a stuck caliper, metal-on-metal contact, or fluid leaks around the brake components.
Professional Diagnosis: Unless you are a qualified mechanic and confident in diagnosing and repairing brake issues, it is always best to have your vehicle inspected by a professional. Brake system integrity is paramount for your safety and the safety of others on the road.
Prevention and Maintenance Tips
Regular maintenance is key to preventing brake issues:
Routine Inspections: Have your brakes inspected regularly, ideally with every service. This includes checking pad thickness, rotor condition, caliper function, and brake fluid levels and quality.
Timely Replacement: Replace worn brake pads and rotors before they reach critical limits. Ignoring wear can lead to more severe and costly damage.
Proper Driving Habits: Avoid aggressive driving that involves frequent, hard braking. Use engine braking (downshifting) when descending long hills to reduce strain on your friction brakes.
Brake Fluid: Ensure your brake fluid is at the correct level and is replaced according to your manufacturer's recommendations. Old or contaminated fluid can lead to caliper issues.
Frequently Asked Questions (FAQs)
Q: How long does it take for new brakes to stop smoking?
A: During the initial bedding-in process, smoke might appear for a few controlled stops (typically 6-10 cycles). After this, and a subsequent cool-down period, the smoke should cease entirely. If it persists beyond this, it indicates a problem.
Q: Is a burning smell normal with new brakes?
A: A slight burning smell during the bedding-in process, accompanying the smoke, is usually normal as the resins and binders burn off. However, a strong, acrid, or persistent burning smell outside of bedding in is not normal and requires immediate investigation.
Q: Can I drive if my brakes are smoking?
A: If your brakes are smoking during the bedding-in process, and it's light and temporary, you can continue the procedure as directed. However, if the smoke is heavy, persistent, accompanied by a strong burning smell, or occurs outside of the bedding-in process, you should pull over safely and have the vehicle inspected. Driving with continuously smoking brakes is extremely dangerous and can lead to brake failure.
Q: What's the difference between brake smoke and steam?
A: Smoke is typically grey, blue, or black, often with a distinct acrid or burning smell, indicating material is burning or overheating. Steam, on the other hand, is white and usually odourless, resulting from water evaporating off a hot surface (e.g., driving through a puddle after heavy braking). While steam is generally harmless, smoke is a warning sign.
Q: Do all brake pads require bedding in?
A: Most traditional brake pads benefit significantly from a proper bedding-in procedure. However, as noted with Bendix General CT pads, some modern formulations are designed to be installed and used immediately without a specific bedding-in process. Always check the manufacturer's instructions for your specific brake pads.
Q: What happens if I don't bed in my new brakes?
A: Failing to properly bed in new brakes can lead to reduced braking performance, inconsistent pedal feel, increased noise (squealing or grinding), premature wear, and even brake judder or vibration due to uneven material transfer or glazing of the rotor surface.
In conclusion, while the sight of smoke from your new brake pads or rotors can be unsettling, it's often a completely normal and necessary part of the bedding-in process. This initial smoke signifies that your braking system is preparing itself for optimal performance, establishing the crucial friction layer that will ensure safe and effective stopping for thousands of miles to come. However, it is paramount to differentiate this temporary, expected phenomenon from persistent or excessive smoke, which invariably signals an underlying problem with your brake system. Always err on the side of caution; if you're unsure about the nature of the smoke or if it doesn't subside after the appropriate bedding-in period, seek professional advice immediately. Your safety on the road depends on a healthy, well-functioning braking system, and understanding these nuances is a key part of responsible vehicle ownership.
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