Domino fade is a characteristic that is common in heavy trucks that often have imbalances between the tractor and trailer's brakes. Light, steady brake applications may not activate all the brakes on a heavy truck. Hard, short brake applications promote more even braking and better distribute heat throughout the brake system. For this reason, it is recommended in the CDL manual that truck drivers use the snub braking technique when operating on steep grades
Domino Fade occurs when some brakes in the system have more brake torque than the others. This imbalance may be the result of poor maintenance, poor load distribution, or light brake applications. The brakes producing more torque will heat up much quicker than they should, which could cause them to fade. If the high torque brakes fail, the other brakes will then receive a disproportionate amount of heat. These now overloaded brakes will also likely fail, hence the domino effect.
Domino fade is a characteristic that is common in heavy trucks that often have imbalances between the tractor and trailer's brakes. Light, steady brake applications may not activate all the brakes on a heavy truck. Hard, short brake applications promote more even braking and better distribute heat throughout the brake system. For this reason, it is recommended in the CDL manual that truck drivers use the snub braking technique when operating on steep grades
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Cars and trucks from Class 1 to Class 6 commonly use a hydraulic brake systems. A hydraulic brake system works by using a non compressible fluid (brake fluid) to transmit the force of a driver pushing on the brake pedal to the brake linings. Air and vaporized fluid are compressible and, if allowed into a hydraulic brake system, the brake pedal will feel spongy and the force transmitted to the lining will be reduced. Just like water, brake fluid can boil and change to a vapor if it gets hot enough. Fluid Fade is the overheating of brake fluid causing it to vaporize. The vaporized fluid will have to be compressed before the system can transmit pedal force to the lining. In most cases, there will be insufficient pedal travel to do both.
The brake fluid used in cars and trucks typically has a boiling point of around 401degrees at sea level. Brake fluid is also hygroscopic, a characteristic which allows it to absorb moisture. Over time, brake fluid will become contaminated with moisture. As this happens, the boiling point of the brake fluid will be lowered, since the boiling point of water at sea level is only 212 degrees. Wet brake fluid has only a 3.5% water content and the wet boiling point of brake fluid drops to 284 degrees. I have tested the boiling point of brake fluid many times and have tested samples that boiled at temperatures as low as 260 degrees. For this reason, brake fluid maintenance recommendations are that it should be flushed about every 4 years. Mechanical Fade is most commonly associated with drum brakes and not disc brakes. In a drum brake, the application of the lining is outward toward the rotating drum's friction surface. As the brake drum heats up, it expands outward. This expansion will increase the drum's diameter, moving it away from the lining application. The expansion of the brake drum causes a need for increased lining travel and increased travel of the application device. If expansion is great enough, it can cause the application device to bottom out and the brakes to fail. A disc brake lining application is at a right angle to the rotating disc and expansion of the disc is outward toward the application rather than away from it. For this reason disc brakes have better fade resistance.
Brake drum expansion is probably the most concerning aspect of brake fade in S-cam braked heavy trucks. In an S-cam brake, the application device is the brake chamber. A typical brake chamber has a maximum pushrod stroke capability of about 2.5 inches. Cold pushrod stroke measurements on a truck with Automatic Brake Adjusters (ABA's) are commonly found to be around 1.75 inches. So, a typical brake chamber will have a reserve stroke of around 0.75 inches. As a brake drum expands away from the brake linings, the cold pushrod stroke will increase. A brake drum temperature of 400 degrees can increase pushrod stroke by as much as 0.5 inches. The force output of a brake chamber is not linear, and a typical brake chamber reaches its knee point where force will begin to drop at about 1.75 inches. If the brake drum becomes hot enough, the brake chamber can bottom out and the brake chamber force output at that point will be 0. Drum brakes are also very susceptible to brake fade because they are self-energizing. In a self-energizing brake, when the lining is applied to the drum, the drum rotation tries to pull the lining and shoe along with it. This self-energizing action increases the force applied to the lining friction surface. When fade reduces friction at the friction surface in a self-energizing brake, a compounded reduction in applied force at the friction surface results in a compounded reduction in braking. The two common types of self-energizing drum brakes used in automotive applications are the Leading-Trailing drum brake and Duo-Servo drum brake. The Leading-Trailing drum brake has a fixed anchor on one side of the shoes. The Duo-Servo drum brake has "floating" anchorage. In a Leading-Trailing brake, only the leading shoe is self-energized. In a Duo-Servo brake, both shoes are self-energized. Therefore, a Duo-Servo drum brake can have a greater reduction in applied force at the friction surface than a Leading-Trailing drum brake and is more susceptible to fade. Friction is the mechanism used to convert kinetic energy into heat in a brake system. Friction is the resistance of motion between two objects that are in contact with each other. If friction at the friction surface is reduced to an unacceptable level, the ability to convert kinetic energy into heat will also be reduced. When a reduction in the friction at the friction surface occurs as the result of heat it is called Friction Fade. When friction fade occurs in a hydraulic brake system, the pedal will still feel hard to the driver, but he will notice a difference in the braking response of the vehicle. For air-braked vehicles, when friction fade occurs, the driver may report the pedal going to the floor.
Brake friction is affected by the temperature at the friction surface. The heat/friction profile is different from lining to lining and can be linear or curvilinear. Either brake lining friction can gradually decline (linear) as heat builds in the brake, or alternatively, lining friction can build-up until it reaches a peak, then quickly begins to decrease (curvilinear). Generally a linear heat friction relationship is more desirable because its fade is gradual and predictable. Brembo is the undisputed global leader in the production of brake discs, calipers and complete braking systems. With its unrivalled expertise, Brembo produces everything from brake discs for the most popular cars in the European, American and Japanese markets to braking systems for the world's most prestigious and exclusive models.
The superlative levels of technology and reliability of Brembo products is founded on an integrated production process which encompasses every stage in the production process, from research and development and testing to casting and machining. On top of this is an ongoing commitment to research and development that sets Brembo apart as a leading name in its industry and allows the group to excel as both a manufacturer of reliable, durable components for the world's most popular and widely sold cars, and as a supplier of state-of-the-art braking systems designed and produced specifically for the most exclusive and desirable models in every class. The drum brake may look complicated, and it can be pretty intimidating when you open one up. Let's break it down and explain what each piece does.Like the disc brake, the drum brake has two brake shoes and a piston. But the drum brake also has anadjuster mechanism, anemergency brake mechanism and lots of springs.
Many drum brakes are self-actuating. Figure 5 shows that as the brake shoes contact the drum, there is a kind of wedging action, which has the effect of pressing the shoes into the drum with more force. The extra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes. But, because of the wedging action, the shoes must be pulled away from the drum when the brakes are released. This is the reason for some of the springs. Other springs help hold the brake shoes in place and return the adjuster arm after it actuates. ![]() One of the more doable jobs in auto repair is that which involves the brakes. The brake rotor provides a friction surface for the brake pads. It is designed to dissipate the heat generated by friction during braking. The ability of a brake rotor to properly disperse heat relates to the size of the brake rotor. The measurement of the thickness of the brake rotor is designed to provide the greatest heat dissipation possible. Machining the brake rotor below those specifications can cause excessive heat build-up during heavy braking. The brake rotor may have cooling fins set in the center to provide ventilation for improved heat dissipation. The surface of the brake rotor is machined to a smooth finish to provide better brake pad to rotor contact and to ensure more even braking. The brake rotor can be easily damaged by metal to metal contact from worn out brake pads. Scoring of the brake rotor surface below minimum thickness levels can quickly occur if the brake pads were worn down to the metal backing plate. Brake rotors can become distorted by improper tightening of the wheel mounting bolts. This can result in warped brake rotors and a pulsating brake pedal. For this reason, wheel mounting bolts should always be tightened to proper torque specifications. When diagnosing and troubleshooting a shaking front end while braking, always consider the possibility of warped brake rotors before engaging in an auto repair brake job. There are three types of disc brake calipers used in passenger cars and light trucks: fixed, sliding, and floating. The fixed caliper is the oldest design of brake caliper in use. They first started appearing on import and domestic performance vehicles in the 1960′s. Most vehicles today use the single piston sliding or floating caliper. Sliding and floating calipers are cheaper to manufacture and more simple in design than the fixed caliper. Basic disc brake caliper operation is accomplished by using hydraulic pressure to actuate the disc brake caliper piston. The caliper can contain up to four pistons, depending on the type used. Each piston is mounted in a bore machined into the caliper. A round, square cut, “O” ring seal is contained in a groove cut into the caliper bore and provides a seal for the caliper piston. A dust seal is placed around the lip of the caliper piston at the brake pad contact area and is secured in a groove on the outside of the caliper bore. A hydraulic seal is maintained through contact of the caliper piston surface with the caliper seal. The caliper seal also provides two other functions in the disc brake caliper. It acts as a brake return spring to maintain correct clearance between the brake pad and the rotor. The caliper seal is able to do this because of its placement in the groove cut in the caliper bore. The seal groove is cut slightly wider than the caliper seal. When the automotive brakes are applied, the piston slides forward in the bore, moving the caliper seal against the edge of the seal groove. This causes the seal to distort in the same direction as the movement of the piston. When the brakes are released, pressure is removed from the piston and the distortion of the caliper piston seal causes it to pull the piston back slightly and create a small amount of clearance between the brake pads and the rotor. This same design allows the piston to move slightly outward as the brake pads wear, when the brakes are applied, due to contact between the seal and the piston surface. When doing an auto repair job involving the brakes, make sure you take note of this very critical design feature. The fixed disc brake caliper uses pistons mounted in the caliper on both sides of the rotor. Hydraulic brake fluid is supplied to both pistons through passages bored inside the caliper. Pressure is applied directly to both brake pads by the reaction of the pistons to hydraulic pressure from the master cylinder. The sliding and floating disc brake calipers generally use one large piston for disc brake pad application. The piston is located on the inboard side of the caliper and directly applies pressure to the inboard brake pad. When the brakes are applied, hydraulic pressure forces the brake piston outward against the inboard pad. That same hydraulic pressure, also forces the caliper assembly in the opposite direction and because the caliper is allowed to float on pins or slide in the mounting bracket, the caliper will provide a clamping action for the outboard brake pad at the same time. This design will use a large piston to multiply the hydraulic force of the automotive master cylinder. The type of brake rotors you need depends greatly on the type of vehicle you drive and the type of driving you do. You’ll find slotted brake rotors, cross drilled rotors and drilled and slotted rotors. And, before you can choose between them, you should understand the basic differences.
Slotted brake rotors feature slots that actually allow the discs to expel built-up brake dust and gases that are generated each time you tap your brakes. So, they don’t just look good, but they’re functional too. And, they work with traditional brake pads or performance brake pads. Drilled brake rotors, on the other hand, do not have grooves, but rather, they have holes drilled through the surface of the rotors. Besides simply looking cool, these holes allow brake dust and gas to vent. Can’t decide between slotted or drilled rotors? Now you don’t have to. A third option exists that combines the best of both worlds—drilled and slotted rotors. These brake rotors feature the stylish slots from the slotted rotors plus the handy holes from the drilled rotors Semi Metallic Brake PadsThese types of brake pads are made from about 30% to 65% metal, and are commonly made out of steel wool, wire, copper or other metal materials. These types of brake pads are considered to be very durable, but also may wear brake rotors faster. Also, semi-metallic brake pads may not function well in very low temperatures.
Non-Asbestos OrganicThis type of brake pad, commonly referred to as NAO, is made from organic materials such as fiber, glass, rubber and even Kevlar. These types of t pads are usually softer and don't create much noise, but they tend to wear faster and create a lot of dust. Low-Metallic NAOThese are made primarily from an organic formula mixture with small amounts of copper or steel added to help with heat transfer and provide better braking. Because of the added metal, there is usually a considerable amount of brake dust and these pads are often noisy. Ceramic Brake PadsCeramic brake pads are composed primarily of ceramic fibers and other filler materials. While ceramic brake pads are usually more expensive than other types of pads, they are cleaner and produce much lower noise levels. Also, they provide for excellent braking and don't cause a lot of wear on the brake rotors.
Brake technology, just like suspension technology and fuel-system technology, has come a long way in recent years. What began in the '60s as a serious attempt to provide adequate braking for performance cars has ended in an industry where brakes range from supremely adequate to downright phenomenal. The introduction of components like carbon fiber, sintered metal and lightweight steel, along with the adoption of ABS, have all contributed to reduced stopping distances and generally safer vehicles (though ABS continues to provide controversy).
One of the first steps taken to improve braking came in the early '70s when manufacturers, on a widespread scale, switched from drum to disc brakes. Since the majority of a vehicle's stopping power is contained in the front wheels, only the front brakes were upgraded to disc during much of this period. Since then, many manufacturers have adopted four-wheel disc brakes on their high-end and performance models as well as their low-line economy cars. Occasionally, however, as in the case of the 1999 Mazda Protege's, a manufacturer will revert from a previous four-wheel disc setup to drum brakes for the rear of the car in order to cut both production costs and purchase price. Why are disc brakes better than drum and how much, if any, loss of braking occurs when using rear drum brakes on a modern car? That's what we're going to find out in this edition of Tech Center. Friction and Heat Before you can appreciate the difference between drum and disc brakes, you have to understand the common principles that both systems use when stopping a car: friction and heat. By applying resistance, or friction, to a turning wheel, a vehicle's brakes cause the wheel to slow down and eventually stop, creating heat as a byproduct. The rate at which a wheel can be slowed depends on several factors including vehicle weight, braking force and total braking surface area. It also depends heavily on how well a brake system converts wheel movement into heat (by way of friction) and, subsequently, how quickly this heat is removed from the brake components. This is where the difference between drum brakes and disc brakes becomes pronounced.
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