Brake System Basics
 

Brake parts account for a substantial portion of most parts store sales today, and should continue to do so in the future. Why? Because many parts in the brake system are high-wear items that have to be replaced every few years. When you add up all of the things that can go wrong with brakes, it's a wonder there aren't more brake-related accidents. Fortunately, most people realize how important good brakes are for safe driving and usually have the brakes repaired when a problem occurs.
Disc brake pads and drum brake shoes are typically replaced several times during a vehicle's life. Most vehicles still have disc brakes in the front and drums in the rear, but a growing number have disc brakes both front and rear. Either way, the front brakes work harder than the rears. Consequently, the front linings are usually replaced two or three times as often as the rear linings.
Brake pads and shoes are sold in matched axle sets (both fronts or both rears) and should be installed in matched sets on the vehicle. Many vehicles are very sensitive to the type of friction material in the linings so you should recommend a premium grade of replacement linings that are the same basic type (or better) of friction material as the OE linings to maintain the same feel, wear and stopping power.
There's a wide range of friction materials used in brake linings today including semi-metallic, ceramic, low-metallic and nonasbestos organic. What's more, many of the friction materials are "application engineered" for specific vehicle applications. When choosing linings, consider how a vehicle is driven and follow the brake supplier's guidelines as to what type of linings would be best for the application.
Ceramic-based friction materials have become popular in recent years because of their stable braking characteristics, low-dust qualities and rotor-friendly nature. Ceramics are also quieter than semi-met and longer lived than most nonasbestos organic friction materials. If a vehicle was originally equipped with ceramic pads, the replacement pads should also be ceramic. Vehicles originally equipped with semi-metallic pads can also be upgraded to ceramic pads in many instances, especially if noise and/or rotor wear have been a problem. Severe-duty users should stick with semi-metallic pads because of their ability to withstand extreme braking temperatures.
Rotors and drums may need to be resurfaced or replaced when the brakes are relined. Some minor grooving of the friction surface is normal, but if the surface is deeply grooved or heavily worn, resurfacing or replacement will be required.
Excessive runout, uneven wear and warpage are others problems that can afflict rotors. Variations in thickness can cause the brake pedal to pulsate, which may also be felt in the steering wheel. Resurfacing the rotors will make them flat again, but hard spots tend to come back after a few thousand miles. The best cure, therefore, is to replace the rotors.
Rotors and drums have wear limits for safety reasons. These parts must have a certain minimum thickness to maintain their integrity and to cool the brakes properly. If the metal is too thin, the rotor or drum may fail. Rotor thickness must be measured with a micrometer before a rotor is resurfaced or reused. The inside diameter of drums must be measured with a drum gauge. If the diameter exceeds specs, the drum must be replaced. Drums or rotors that are cracked or damaged must also be replaced.
Calipers apply the brakes in a disc brake system, while wheel cylinders perform the same job in drum brakes. Both use pistons and hydraulic pressure to apply the brakes. The main problems here are fluid leaks due to seal wear or damage, and piston sticking due to corrosion.
Many experts recommend rebuilding or replacing calipers and wheel cylinders when the brakes are relined in high-mileage vehicles - even if the original parts are not leaking or sticking. Why? To reduce the risk of a comeback. Calipers and wheel cylinders are the lowest point in the hydraulic system and tend to collect moisture and sediment. As a result, internal corrosion often leaves pistons and bores pitted and rough.
Calipers are sold as bare units (new or remanufactured) or as "loaded" assemblies with new pads, shims and hardware. Loaded calipers provide everything your customer needs in one box and with one part number, which makes for easier installation.