If you have worked on brakes or pushed brakes past their limit, you know how they tend to smell. Some people like the smell, but most do not. Most drivers may not know much about their vehicles, but they know when something does not smell right.
Customers who come back to the shop for a smell-related issue are usually not too happy. For shops, it is a difficult phenomenon to explain. And, to complicate matters, the smell is typically gone by the time they get back to you, if they come back at all. Even though there is nothing wrong with the vehicle mechanically, you still have to set the customer’s concern to rest.
In extreme cases involving fleet vehicles that are used to transport people, the smell might cause the driver to park the vehicle in fear that the smell is a mechanical issue that could impair the safety of the vehicle.
The source of the smell is typically the brake pads. Explaining the source to your customers is very difficult because you are treading on very complicated brake pad chemistry.
The term and concept that you want to avoid using at all costs is “burning off.” This is inaccurate and may cause the customer to become alarmed. Yes, there is heat involved when the bad smell is produced, but it is not oxidation or burning.
What is really happening is polymerization, or “curing.” This is a chemical process where smaller units are combined into larger and more stable units. It can be compared to making an omelet. When heat is applied to the eggs, the omelet is formed. But, in the case of the friction material, the yoke and whites are the resins that hold the pad together.
The heat of braking causes the resins to polymerize and form stronger bonds, which is a good thing. The bad thing about this process is when the resins polymerize, they also create byproducts in the form of gases that do not smell pleasant.
The bottom line is that the smell is not a bad thing in the majority of cases for new pads. What is important is that the pad be heated in a controlled manner.
If the pad is heated too quickly or outside a certain heat range, the friction material could lose strength and the gases given off could cause brake fade. But, if the pad is broken-in correctly, the gases do not pose a problem and brake fade conditions can be minimized in the future.
Preventing the Smell Comeback
Just about every brake pad manufacturer has a specific break-in procedure or they recommend no break-in procedure at all. The break-in procedure beds the pads to the rotor and induces heat that starts polymerization on some pads.
Break-in procedures can vary from 10 to 20 stops from 30 mph, to moderate driving with no heavy braking for the first 500 miles. How can anyone explain the discrepancy?
First of all, all brake pads are different in their formulation and manufacturing methods. One manufacturer may use a molding technique that may use less resin and more heat in the molding process. Another manufacturer may use a special resin that may work great, but has a distinct smell when being polymerized. That’s why it is tough to make generalizations or judge a pad on its recommended break-in procedure.
Just understand that if a manufacturer recommends a break-in procedure, follow it to the letter. Do not just pump the pedal a few times and back it out of the bay and hope that the customer has a sinus problem. Even if the pad specifies a 500-mile moderate braking procedure, take the car for a test-drive.
If you are not comfortable with the smell or have problems with customers complaining about it, it might be time to switch your brake pad brand.