When you are buying a legal drug, you are not just paying the cost to manufacture, package and market the pill.
By Andrew Markel
Buying a quality brake pad is like buying medicine. When you are buying a legal drug, you are not just paying the cost to manufacture, package and market the pill. The bulk of what you are paying for is research and development. The same is true for brake pads.
Aftermarket brake pads require a great deal of testing and engineering because they are made for a specific vehicle. A quality brake pad manufacturer will spend a lot of time and money developing a brake pad application for your vehicle. This includes simulated and on-the-vehicle testing. These types of testing are time and equipment intensive.
As a technician, it can be difficult to judge a brake pad before you put it on the vehicle. But, doing your homework and looking for certain visual cues can help you make the right choice.
Ceramic material’s structural properties are very stable under high temperatures, much like Corning cookware. But this is where the comparison ends. Ceramic materials that go into a brake pad are very small strands that are engineered to be a certain length and width. There are three advantages of ceramic pads in certain applications. First, since the ceramic materials offer stable performance under a wide range of temperatures, they can offer quiet performance. Second, ceramic brake pads manage heat in the caliper better on some vehicles than some non-ceramic applications. Third, ceramic brake dust does not show up on or stick to wheels like some other brake pad formulations. This could be an important factor if you have an expensive set of custom wheels.
Semi-Metallic pads use metal fibers to give structure and provide friction. The metals used are typically high-quality steel, copper and other exotic metals.
So what is the other part of the semi-metallic mix? It is a variety of materials like glues, lubricants and structural fibers. The manufacturer will blend the components together to give the best performance for that application.
If all of the material jargon is too much to deal with, you can look for a line that touts itself as vehicle or application specific. These lines can help you leave the material selection up to the manufacturer.
What makes one friction material quieter or better than another? It is a two-part answer. First, if a friction material is better at keeping a constant coefficient of friction across broad temperature ranges and environmental conditions, it probably is a quiet pad. A “consistent” friction material causes less vibrational excitation variation at the friction coupling by having consistent brake torque at environmental extremes of humidity and temperature (-40 F to 500 F).
Second, some friction materials leave or transfer a layer of friction material (transfer film or “seasoning”) on the rotor’s surface that some friction material companies claim can smooth out the rotor surface, thereby causing less excitation and noise at the friction coupling. Also, this transfer layer may not be as sensitive to heat-induced brake torque variation.
The backing plate creates a foundation for the friction material that must be stiff and stable. If a backing plate is flexing, the friction material is not in full contact with the rotor. This can cause longer stops, a softer brake pedal, and it increases the potential for unwanted noise.
Look at the thickness of the backing plate and the edges. A poorly stamped backing plate will have rough edges. Also, look at the areas where the pad contacts the caliper. These areas should be as smooth as possible.
The attachment method of friction to the backing plate does matter. For some fleet and safety-critical applications like school buses, the manufacturer or insurance company may specify a brake pad that uses a mechanical attachment to secure the friction material to the backing plate. Mechanical attachment involves some type of protrusion from the backing plate to hold the friction material. Some backing plates have tiny hooks machined into the surface to hold the material.
Another aspect to look at is the shape of the friction material on the brake pad. OEMs tune the shape of the brake pad to the overall system. This includes elements like overall length and width, and design elements like chamfers and slots. These physical dimensions and design elements can reduce excitation and shift natural vibrational frequencies. Some aftermarket brake pad manufacturers will tune the shape of their pads to suit older vehicles and the characteristics of their friction material blend.
Look at the shim material on the back of the pad. If possible, remove the shim and drop it gently on a hard surface. If the shim makes a nice “thunk,” it is made of a good material. If the pad makes a rattling sound, like a dropped wrench, chances are it will not make a good sound insulator.