With the introduction of numerous application-specific and performance-enhanced brake pad materials into the jobber inventory, recommending a brake pad to fit a customer’s pocketbook has become a somewhat thorny issue for today’s counterman. After all, does today’s soccer mom really need the high-dollar ceramic pads to shuttle her kids to sports contests or, for that very reason, does she need more safety than an average brake pad can provide?
Due to the introduction of ventilated alloy wheels and advanced friction materials, engineers have been able to reduce the rotating mass of most brake assemblies. Obviously, using a ventilated wheel to increase the airflow around the brake assembly will help keep it cool. Next, using an advanced friction materials also allows the brake to operate at higher temperatures. Last, anti-lock brake technology tends to distribute wheel-to-wheel braking stresses more evenly during emergency stops. The results are lightweight disc brakes that work very well under most conditions. Unfortunately, problems develop when a brake assembly may be designed too small for specific situations, such as emergency vehicle or police service. In these instances, the major complaints will be poor braking and service life. In some cases, these issues can be addressed with improved aftermarket pads and rotors. In other cases, the vehicle will become one of those that require caution when recommending friction materials and replacement brake rotors.
Although the industry does have manufacturing standards for friction material in the form of the ‘edge codes’ found on brake pads, it’s important to understand that friction manufacturers may use different materials and formulations to meet a particular performance standard. Back in the 70s when disc brakes were first introduced, conventional asbestos friction materials worked very well on the massive vented disc brake rotors in use. When asbestos is used, the rotor itself absorbs and dissipates the heat generated during braking. When semi-metallic materials were later introduced and installed on some of these applications, many installers found, since semi-metallic material conducts heat better than asbestos materials, the brake pedal felt less responsive because the massive rotors ran too cool for the semi-metallic materials to engage under normal braking. Also, with the advent of metallic linings, the brake caliper itself had to be redesigned to prevent excessive heat from being transmitted through the pad into the brake caliper piston and eventually into the fluid itself. During severe braking, this heat transfer could boil the fluid in the brake caliper which would cause a catastrophic loss of braking force. In most cases, a phenolic or "plastic" caliper piston is used to help insulate the brake fluid from heat transmitted by the semi-metallic pad.
Some pad compositions, such as ceramic, may not work universally well in all applications because of compatibility issues with the brake rotor. To illustrate, we now have a wide array of replacement brake rotors, including "white-box" replicas, coming into the market place, which may not be equal in specification to the OE-equivalent replacement. Many independent repair shops, for example, prefer installing premium-line rotors with ceramic pads because they seem to have the least number of noise and pulsation complaints. In other instances, shops have found that when a ceramic pad is used for severe-duty applications, the pad might require a dimpled or cross-drilled rotor designed to vent gases that form between the pad and rotor during severe braking.
Regardless of composition, the performance of a pad is usually directly proportional to price. Clearly, when prices are reduced, one or more of the qualitative aspects of brake pad design are usually sacrificed. The lesser-priced pad, however, has a definite place in both the mass and price-sensitive markets. Sure, the homemaker doesn’t need the latest in high-performance friction for her daily trip to the supermarket. But on the other hand, it’s equally important not to underestimate the important of performance friction to the retiree who may be towing a fifth-wheel trailer home through mountainous terrain. SERVICE ISSUES
Several schools of thought prevail in the current brake service market. First: Many manufacturers, for example, feel it’s sufficient to clean and lubricate the caliper guides and install new brake pads on the old rotors, providing no pedal pulsation complaints exist. Second: Because the price of new brake rotors has significantly decreased, many shops would rather replace than resurface some rotor applications. Third: Many automakers and friction material manufacturers now recommend on-vehicle resurfacing equipment. Fourth: It’s extremely important to refinish the rotor as smoothly as possible and to remove microscopic iron particles by washing the brake rotor in soap and water.