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Automotive Q & A

Brakes

Question: How does a brake system inspection work?

Answer: Brake system inspection is an absolute must to ensure safe driving conditions. During a brake inspection the entire brake system is checked; this includes the following: the brake pedal, brake fluid, brake lines and hoses, and the brake assemblies (whether they are disc brakes or drum brakes). Parking brakes should also be checked at this time. Checking how your brake system is working starts with your brake pedal. There are three things to check when it comes to your brake pedal. The brake pedal’s height should be checked along with measuring free play and the brake pedal reserve distance. All of these measurements should be compared with the vehicle manufacturer’s specifications. The brake pedal height is the measurement of the brake pedal to the floor when the brake pedal is at rest. Free play means that when you step on the pedal the brakes aren’t applied right away. The free play is measured by the pedal movement from rest until the brakes are actually applied. Pedal free play is actually required, but it is important the free play measurement is in accordance with the specifications of the manufacturer. Lastly is brake pedal reserve distance. This is the distance from the pedal to the floor when the brakes are applied. So, if your pedal’s height is off or if there is excessive free play, there may be problems with your pedal bushings and return springs. If the reserve distance is incorrect, there may be problems with the cylinder pushrod. Next, your brake fluid should be checked. Brake fluid provides the necessary force to activate your brake shoes and compress the brake pads or brake shoes. Brake fluid is kept in the master cylinder and experts say it should be changed every year or two to ensure your brakes will work properly. Along with checking the brake fluid, the hoses and lines should be checked. If the master cylinder is low, there may be a leak somewhere in the lines. The lines and hoses can be visually checked for cracks, and the actual brake assembly can be checked for moisture. You can also place cardboard under your vehicle and step on your brakes several times. Then check the cardboard for any leaks. Finally, the brake assemblies are checked. To inspect the brakes, your front and rear wheels are removed to get a better view of the brake assemblies. There are two different types of brake assemblies: disc brakes and drum brakes. Let’s discuss inspecting disc brakes first. There are three things that must be inspected on disc brakes: the brake pads, brake rotor, and the caliper. The brake pads are located on each side of the rotor and are actually pushed against the rotor to stop the wheel and stop your vehicle. The pads create the necessary friction to stop the vehicle. The pads are checked for excessive wear to make sure there isn’t metal rubbing on metal. The brake rotor is the iron disc that is connected to the tire’s hub. Rotors must be inspected for excessive wear. Brake pads and rotors have matching wear patterns, and if a brake pad needs to be replaced, the rotor will have to be machined smooth. A rotor can be machined smooth only so many times before it is worn too much. Each rotor must have a certain width, which is inscribed on the rotor, and if the rotor is too worn, it must be replaced. The rotor should also be inspected for any heat cracks or other damage. The last part of a disc brake is the caliper. The caliper is a device located over the top of the rotor and contains both brake pads. There are two types of calipers: floating calipers and fixed calipers. A floating caliper can compress itself and contains only one piston. When the brakes are applied, brake fluid will force the piston into the brake pad, which will press against the rotor. Then the other side of the caliper will press the other brake pad against the rotor to stop the wheel and vehicle. A fixed caliper doesn’t move; so, it contains two pistons located on each side of the rotor. When the brakes are applied, brake fluid forces both pistons into each brake pad which press against each side of the rotor to stop the wheel and vehicle. Calipers must be inspected to check for leaks. The second type of brake assembly is the drum brake. Drum brakes are usually located on rear wheels because of the need for a parking brake. Parking brakes are added much easier to a drum brake than to a disc brake. Drum brakes contain several different parts: brake shoes, which are like brake pads; a backing plate, which basically holds everything together and is attached to the axle; brake drum, which is like the brake rotor; wheel or brake cylinder, which contains the pistons; return springs; and a self-adjusting system that will adjust the position of the brake pad when the brake isn’t applied. When the brakes are applied, brake fluid forces the pistons to push against the brake shoes, which press against the drum, which will stop the wheel and vehicle. Then, when the brake is released, the return springs send the brake shoes back to their original position. Brake shoes are located very close to the drum so that when you step on your brake pedal, the brakes are immediately applied. Over time, the surface of the brake shoes wears and the position of the shoes must be adjusted so it doesn’t have to travel a farther distance to come into contact with the drum. If the drum brakes didn’t have a self-adjusting system, you would have to press down farther and harder on your brake pedal before the brakes would be applied. When a drum brake is inspected, there are many more parts that need to be checked than in a disc brake. The brake shoes need to be checked for excessive wear so they don’t damage the drum. The brake drums, like the rotor, need to be checked for excessive wear or cracks. They also have to be machined smooth when a brake shoe is replaced and can only be machined down so far; then they must be replaced. Wheel or brake cylinders need to be inspected for any signs of leaking. The return springs need to be checked because if they are too worn and don’t return the brake shoes back to their original position, away from the drum, the brake shoes can experience rapid and excessive wear. Finally, the self-adjusting system must be inspected to make sure it is clean and properly lubricated. Parking brakes should also be inspected at this time. A parking brake, or emergency brake, must be inspected to make sure that the cables and levers are working properly. Parking brakes work separately from your regular hydraulic brakes. They are a necessity to keep your vehicle from rolling down a hill when it is parked. It must also be working properly if your regular hydraulic brakes ever fail.

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