Brake Repair: How to Diagnose, Fix, or Replace Your Car's Brakes Step-By-Step. Cartwright
show the factory formulation in bold print and options such as severe-duty or ceramic in lighter print. For the average driver, it is probably best to stay as close to the factory formulation as possible because the original equipment manufacturer (OEM) engineers likely spent a lot of time and money to decide that they were the best! Pads are sold in axle sets, so one box does both the left and right sides.
Some pads have chamfered edges and slots that are intended to reduce noise from vibration or to channel away gases and wear particles. Replacement pads may differ in appearance from originals. If they are from a trusted manufacturer, they might perform better than the OEM design, but be sure they fit properly and are listed for your vehicle in their catalog.
Even though the original OEM is held to strict government Federal Motor Vehicle Safety Standards (FMVSS 135) regarding original equipment brake performance, the aftermarket does not have many restrictions on brake pad material or design. It is best to stay with a name brand and not to shop for brake pads based on price alone.
Rotors
Most brake rotors are a one-piece design made of cast iron or a composite design using a steel plate with a cast-iron friction surface. Performance applications, such as late-model Corvettes, use carbon-ceramic rotors, which are not metal. They are expensive but handle heat extremely well and weigh about 11 pounds less than a comparable cast-iron rotor. This reduces unsprung weight, improving handling and ride and reducing overall vehicle weight, which improves performance and reduces emissions.
Many performance vehicles come from the factory with carbon-ceramic rotors. The main advantages are superior braking and weight reduction for handling, performance, and fuel economy. Less unsprung weight means better handling. Less overall weight (approximately 50 pounds) means improved performance, better fuel mileage, and lower emissions.
Often the front rotors are a vented design with cooling fins between the two friction surfaces. If your vehicle is equipped with rear disc brakes, the rotor can also be a one-piece plate without cooling fins because they don’t have to deal with the heat that the front brakes do.
Some performance vehicles are equipped with drilled and/or slotted rotors from the factory. This is to assist with channeling gases and wear material away from the contact surfaces between the rotor and pad and improve brake performance.
Aftermarket components to add these features to your existing vehicle are available. Purchase from a reputable source to be sure that you are getting an actual improvement in brake performance. Performance systems may include larger diameter rotors and upgraded calipers and can be quite expensive.
Use Caution with Brake Fluid
Some technicians prefer to wear disposable gloves when working around brakes and brake fluid.
You may not have the same “feel” at your fingertips when handling small parts such as copper washers, but disposable gloves are relatively thin so that they can work. They are usually available in boxes of 100 for less than $10. Caution: Brake fluid is extremely damaging to paint, so be extremely careful when you are working with it. ■
Vehicles may be equipped with drilled and slotted rotors to reduce heat and for channeling wear particles away from the rotor surface. Aftermarket brake upgrade kits with these features are also available for many applications.
Some may look good through the wheel but actually cause the brakes to run hotter due to a reduction in rotor mass. They could just be the factory type of rotor with holes drilled in them.
Inspection and Diagnosis
Disc brakes can become worn without displaying warning signs. There will be no change in pedal height or feel and the vehicle continues to stop until the friction surface is completely worn away. Some vehicles have audible wear sensors attached to the brake pads that make contact with the rotor surface, causing a high-pitched squeal when the pads are almost worn out. This is usually heard when the brakes are not applied.
It is sometimes difficult to view the condition of the pads and rotors without removing the wheel. This is especially true of the backside of the rotor and inboard pads. Some applications have a full backing plate on the inboard side of the rotor to protect it from contamination, which greatly restricts visibility.
You may be able to get a partial view of the outboard pad and rotor surface through the wheel, but a thorough inspection requires wheel removal to get a good look at the entire system because a backing plate hides the inboard pad and rotor surface from view.
Most brake pads have a metal wear sensor (arrow) that is designed to scrape against the rotor when the pads are almost worn out. Its purpose is to alert the driver that brake service may be required soon.
If the sensor is ignored, the metal backing plate or rivets make contact with the rotor face when the friction material wears away and causes severe damage to the rotor surface. If the metal-to-metal condition continues, the area where the pads contact the rotor can become completely worn away and the caliper piston can come out of the rotor, causing hydraulic failure and complete loss of braking on that circuit.
Some high-end vehicles have electronic sensors that cause a warning lamp on the instrument panel to appear when the pads are nearing the end of their life. This design generally uses a brush-like material to ground a circuit through the rotor.
Ignoring the warning signs can lead to more expensive repairs. This rotor was severely damaged because the friction material on the pad was completely worn away and metal-to-metal contact was the result. Much noise resulted but was apparently ignored.
This is an example of a brake pad that was worn past the friction surface and into the steel backing plate. Most of the time, the rotor is damaged to the point of requiring replacement.
Most luxury and German vehicles have electronic wear sensors. This type of sensor completes a circuit to ground when the pads are nearing the end of their life. A warning lamp on the instrument panel is illuminated so that the owner knows that brake service will be required soon.
Another telltale sign of brake pad wear is low brake fluid level in the master cylinder reservoir. If the fluid level is extremely low, a brake indicator lamp may illuminate on the instrument panel.
Low fluid level in the master cylinder is caused by a hydraulic system leak or disc brake pad wear. As the pads wear and their thickness diminishes, fluid must take up the void behind the caliper pistons, which leads to less fluid in the master cylinder. This master cylinder has a sensor (arrow) that turns on a dash light when the fluid level is low.
The Test Drive
The first step in assessing a disc brake system is a thorough test drive. Listen for noises and watch for pulling to the left or right when the brakes are applied. Observe the brake pedal height and feel of the pedal when stopping. See if the force required to stop the vehicle is abnormal. If the pedal moves up and down (pulsates), the rotors may need attention. If the pedal is unusually low, the drum brake system may need adjustment or repair. There could also be an issue with the ABS system.
On disc brakes, a low pedal does not result