HDABOB's Tech Notes:
Do you ever wonder how the brakes work?
Let me explain it to you...
The components of the braking system consist of:
Anti lock system
ABS indicator light
Every car manufactured has either disk or drum brakes, or a combination of both types of brakes installed on the front and rear of a vehicle.
On most cars, front brakes are of the DISK type. What that means is that there is a rotating metal disk attached to the front axle. There is also a pair of fiber BRAKE PADS equipped with wear sensors inside CALIPERS attached to the non-rotating part of the hub. The disk rotates between the two pads. This means that the pads are always in contact with the rotor.
When you step on the BRAKE PEDAL, the BRAKE FLUID from the MASTER CYLINDER is pressurized and magnified by the BRAKE BOOSTER attached to the brake master cylinder. The brake fluid under pressure then goes out to each wheel through PROPORTIONING VALVES, distributing pressure to each wheel depending on weight distribution. The harder you step on the pedal, the more pressure is applied to the brakes, eventually locking the wheels. The brake fluid is a hydraulic fluid designed to withstand extreme pressures and temperatures without boiling or foaming. Brake fluid is essential for proper brake operation. The brake system must contain NO air or moisture. Either substance will degrade the brake system considerably. Air will cause the brake pedal to be spongy. Water causes corrosion and will degrade the ability of the brakes to operate safely.
In stop and go traffic when you are using the brakes a lot, the rotors get very hot...around 300 degrees. When they get that hot they expand from their usual thickness about three to five thousands more. When you stop at a stoplight and hold your foot on the brakes for approximately 3 minutes, the area just under the brake pads is under more pressure, so, it gets much hotter...about 400 degrees. This area expands even more, causing the rotor to "WARP". This area is permanently thicker than the rest of the rotor, thereby causing a sometimes violent vibration only under braking. This problem can only be repaired by replacing the rotors. Turning the rotors will solve the problem only temporarily, because when you turn rotors, metal is taken off until the rotors are parallel, so with less metal on the rotor, it heats up even faster and "WARPS" even worse than before. So, to keep your brake rotors straight and smooth, replace brake pads at the first sound of the sensor device and don't keep your foot on the brake at stoplights. If necessary, use the emergency brake or creep slowly to equalize the heat all around the rotors.
The BRAKE LIGHTS are activated anytime the brake pedal is depressed very slightly. Do not rest your foot on the brake pedal while driving. This turns on the brake lights and wears out the brakes. There is a foot pad for your left foot, use it instead. An easy way to see if your brake lights are working is to blow the horn. The brake lights and the horn are on the same fuse. If the horn doesn't work, it's a good bet that the brake lights are out. If the vehicle indicator on the dash is showing a problem with the brake lights, the problem is probably one of the brake light bulbs has burned out. Remember, there is another brake light in the rear window (and on the wing if installed) on all new cars.
Drum brakes (usually on the rear) consist of a rotating drum with the wheel attached, and two expanding BRAKE SHOES: curved metal pad with fiber around the outer arc, which is attached to the non-rotating part of the hub. When brake pressure is applied, a WHEEL CYLINDER between the brake shoes expands the shoes outward toward the inside of the drum. This creates friction slowing the rotating part of the drum with the wheel attached. Drum brakes are not susceptible to "warping" as on brake rotors because they do a lot less work in the rear of a vehicle than do rotors in front. They don't get as hot.
The brake pedal should always be firm. There is no air allowed in a hydraulic brake system. All air is bled out during servicing.
The EMERGENCY BRAKE expands the brake shoes or compresses the rear brake rotors by means of a mechanical device. It does not depend on brake fluid pressure and activates the rear brakes only. When the emergency brake is pulled up, a light in the dash illuminates. If this light stays on after the emergency brake is released, or comes on when turning a corner or braking, it indicates a low brake fluid condition. The brakes must then be checked for leaks or necessary brake work.
…and that’s how the brakes work!
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HDABOB's Mobile Service 09/15/2007