| About the Braking System |
| What are the basic function of an automotive braking system? |
| By pushing on the brake pedal hydraulic fluid is forced from the master cylinder through the brake lines down to the pistons in the calipers or wheel cylinders forcing them to expand putting pressure on the pads or shoes. On disc setups the caliper piston squeezes the brake pads against the rotor, on drum setups the wheel cylinder piston pushes the brake shoe against the drum causing the wheel to stop. This is just a part of what is happening. The Braking system is basically an instrument that changes energy. When moving your car has kinetic energy by applying the brake the kinetic energy is converted into thermal (heat) energy via friction created by the pads rubbing against the rotors. The cooling of the brakes dissipates the heat and the vehicle slows down. |
| What dose a typical automotive brake system consists of? |
| • Brake Pedal
• Power Booster
• Hydraulic Master Cylinder
• Brake Fluid
• ABS System (optional)
• Proportioning Valve
• Brake Hoses and Line
• Brake Rotors
• Drum Brakes.
• Calipers
• Wheel Cylinders
• Brake pads
• Wheel and Tiers |
| What is the Power Brake Booster? |
| The Power Brake Booster amplifies the pressure applied to the brake pedal so that less foot pressure is needed to apply the brakes. There are different types Power Brake Booster the most popular are the vacuum and the hydraulic type. A Vacuum Power Brake Buster works by using engine vacuum. Engine vacuum is hosed to the Brake Buster via a one way check valve. A diaphragm inside the busters provides the power assist when pressure is applied to the brake pedal. A Hydraulic Power Brake Buster works by using hydraulic pressure generated by the power steering pump and stored in an accumulator located behind the Master Cylinder. The accumulator amplifies the foot pressure applied on to the brake pedal. |
| What is a Brake Master Cylinder? |
| What is a Brake Master Cylinder? The master cylinder is a hydraulic pump powered by your foot which converts non hydraulic pressure to hydraulic pressure to move components at the other end of the braking system. The pressure created by your foot is transferred by the master to the pistons in the caliper or wheel cylinder. The Brake Master Cylinder is located in the engine compartment usually on driver side and also contains the brake fluid reservoir mounted on top. For safety the master cylinder is typically separated in two circuits, it has two pistons in one cylinder each supplying one circuit of the brake system. If one piston fails the other circuit will still work allowing the vehicle to stop. |
| What is Brake Fluid? |
| Brake fluid is formulated to withstand high temperatures without boiling and cold temperatures without thickening. Brake fluid is also designed to absorb moisture so that it won’t collect causing rust or freeze in cold weather. All brake fluids must meet standers set by the Department of Transportation.
Specific qualities of Brake Fluid · Dose not freeze or thicken at cold temperatures.· Must not compress.· Must flow through small holes.· Must not corrode brake system components.· Lubricate moving parts.· Dose not decompose or form gum or sludge,
DOT 3 Spec - Dry BP 401 - Wet BP 284 - BP after 6 months 343
DOT 4 Spec - Dry 446 - Wet BP 311 - BP after 6 months 379
DOT 5 Spec - Dry 500 - Wet BP 346 - BP after 6 months 423
Castrol LMA - Dry 450 - Wet BP 311 - BP after 6 months 381
ATE SL - Dry 500 - Wet BP 329 - BP after 6 months 415
Valvoline High Perf Synpower - Dry 503 - Wet BP 343 - BP after 6 months 423
Motul DOT 5.1 - Dry 509 - Wet BP 365 - BP after 6 months 437
Gunk DOT 4 Brake Fluid - Dry 510 - Wet BP 311 - BP after 6 months 411
ATE Type 200/ATE Super Blue - Dry 536 - Wet BP 392 - BP after 6 months 464 |
| What is the Proportioning valve or Equalizer Valve? |
| The Proportioning valve are designed to adjust the pressure between the front and rear brakes. Usually mounted on the fire wall bellow the master cylinder. The valve directs less pressure to the rear brakes to preventing premature lockup under heavy braking. |
| What are the Brake Hoses and Brake Lines? |
| The brake lines and hoses transfer brake fluid pressure from the master cylinder to the calipers or wheels cylinder. Brake lines are usually made of bent steel tubing wile standard brake hoses are made of reinforced rubber. Also available in the aftermarket are Stainless Steel Braided Performance Brake Hoses, these houses reducing expansion which improve braking and provide a firmer pedal feel. |
| About Brake Rotors |
| What is a Disc Brake Rotor? |
| The Brake Rotors is a meager component of the braking system. The Rotor is a device used for slowing or stopping the rotation of a wheel while it is in motion. Disc Brake Rotors are found on many different types of vehicles, from bicycles to airplanes and are made of many different materials. The most commonly used in road cars and trucks are made of cast iron. Cast iron is used because it absorbs and dissipated heat well, resists ware and is inexpensive compared to other metals.
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| What are the different types of Brake Rotors? |
Solid Disc Brake Rotor:
This type of rotor does not have any cooling fins in between the rotor faces. Solid rotors are usually use in the rear or on smaller lighter vehicles. Vented Disc Brake Rotors:
Vented Brake Rotors have cooling fins or vanes between the rotor faces for better cooling. The vented rotor works like a centrifugal pump by moving air from the center of hub outward. The air moving through the vanes cools the rotor. There are many types of vane configuration, strait vanes, curved vane and some have segmented vanes. The different type cooling vanes configurations are used to maximize cooling and reduce harmonics that can contribute to break squeal
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| What is Brake Rotor wear? |
| Disc Brake Rotor rotors are a wearing component of the braking system and must be checked periodically for wear and tear. All rotors are stamped with a minimum thickness measurement this measurement is used by a technician to determent when a rotor needs to be changed. Once the rotor wares below the minimal thickness it ability to absorb and dissipated heat is reduced and must be changed. |
| What are the operating temperatures of a Brake Rotor? |
| The Brake Rotor must hold and dissipate heat during the conversion of kinetic energy to heat energy. The temperature of the braking surface can increase by up to 200 degrees on one stop from 55 MPH. A few hard stops or riding the brakes down a steep hill and temperatures can get up over 800 degrees. The heavier the vehicle the more heat it will produce during braking and need to use heavier and larger rotors.
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| What are Disc Brake Rotor Made of? |
| Cast iron is the most commonly used material to manufacture rotors, because it absorbs and dissipated heat well, resists ware and is inexpensive compared to other metals. The metallurgy of the cast iron is very important because it determine the strength, wear, noise and the braking characteristics of the rotor. When produce a quality Rotor the casting process must be carefully controlled or the iron may not form the proper microstructure. A rotor that is too soft may ware prematurely or a rotor that is to hard may crack. |
| Brake Rotor Problems |
| What is Disc Brake Rotor Runout? |
| It is very important to check runout when doing a brake job, especially when installing new rotors.
Brake Rotor Runout is the measurement to determining whether the rotor axis is parallel to the spindle axes. If the runout is too high it will result in a high and low point on the rotor contacting the brake pads causing pulsation in the brake pedal under braking. The runout can also occur if the rotor is unevenly warn and is thicker and thinner in different locations on the brake contact surface called Disc Thickness Variation (DTV). |
| What is the Runout tolerance? |
| Runout tolerances can vary for different vehicle. Some vehicles are more sensitive to runout than others. Usually lighter vehicles with lighter suspension are more sensitive and require smaller runout. Also a warn brake, suspension and steering components will also amplified the vibration form the rotor runout. To measure runout a dial indicator is needed. The dial is placed on the face of the rotor, the rotors is turned slowly while reading the dial. If the runout exceeds factory specification it will need to be correcting to avoid vibrations.
When installing new rotors in many cases runout can be corrected by removing the rotor and repositioning it on the hub, make sure that the rotor and hub mounting surfaces are clean, clean, clean. If repositioning the rotor dose not reduces the runout, it can be corrected by placing shims in between the rotor and the hub. Shims of different thicknesses are available to correct the runout. |
| When can Runout occur? |
| Runout can occur due to:
• On even brake friction build up.
• Improperly torque wheel lugs.
• Bad resurfacing.
• Rust build up in between the rotor and hub.
• Rotor Warping.
• Warn wheel bearing.
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| What is Rotor Warping and Pulsation? |
| The words warped rotors are the most commonly used to describe Brake pulsation and vibration problems. But this is incorrect rotors don’t actually warp. Brake vibrations and pulsation are caused by Brake Torque Variation (BTV) and Disc Thickness Variation (DTV) individually or in combination. Brake Torque Variation (BTV) is a variation of torque across face of the rotors braking surface. This variation cassis the brake pad to slip and catch as the rotor rotates. BTV is usually cased by uneven deposits of brake pad material on the rotor surface or by hard spots usually do to the metallurgy of the brake rotors. The torque variation will case vehicle to vibrate or judder and may or may not be felt in the brake pedal.Disc Thickness Variation (DTV) is the defense in thickness at multiple spots around the rotor braking surface. This variation in thickness increases runout and causes the rotor to push the Caliper Piston in and out. This movement crates vibrations and pulsation that are transferred trough the brake pedal and the chassis. |
| Brake Pad Problems |
| What is Brake fade? |
| A reduction or loss in braking force due to loss of friction between the disc pad and the rotor. Fade is caused by heat build-up through repeated or prolonged brake application
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| What is Outgassing? |
| At high temperature the resins in the bake pad vaporize forming a barrier between the pad and rotor. This barrier cusses the brakes to fade. When outgassing occurs there is still a firm brake pedal but the amount of friction being generated is reduced. |
| What is Creep Groan? |
| A noise that occurs at very low vehicle speed (under 2 mph) when applying or holding the brake ON. Creep groan is caused by brake lining "stick-slip". It usually experienced on vehicles with automatic transmissions. |
| What is Brake Judder? |
| A Vibration during braking at low speeds which is caused by Disc Thickness Variation. Brake judder vibrations and are transferred trough the brake pedal and the chassis. |
| What is high speed Brake Judder? |
| A Vibration during high speed braking. It is caused by Brake Torque Variation, hot spots and on even brake material transfer on the rotor. High Speed Brake Judder vibrations are transferred trough the chassis. |
| What is Brake Howl? |
| Brake Noise generated in the range of 500 to 1,000 Hz and caused by stick slip. |
| What is Rotor scoring? |
| Grooves on the friction surface of the brake rotor, usually caused by the brake pads. |
| What is Low Frequency Brake Squeal? |
| Noise generated in the range of 800 to 5,000 Hz and caused by the positive mechanical feedback excitations from the brake linings.
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| What is high frequency Brake Squeal? |
| Noise generated in the range of 5,000 to 18,000 Hz and caused by the positive mechanical feedback excitations from the brake linings |
| What is Stick-slip? |
| Stick-Slip is caused by a non-linear change in the coefficient of friction. When the coefficient of friction increases, the two surfaces will stick. As the rotational force increases or the coefficient of friction decreases, a sudden release or slip will occur between the two surfaces. |
| What is a transfer layer? |
| The transfer of friction material to the brake drum or rotor. The thickness increases with temperature and the number of braking cycles; thickness is also directly related to the amount of stick-slip. |
| About Brake Pads |
| What are Disc Brake Pads? |
| The brake pads are made components of the brake system. They consist of a steel backing plate and a molder, bonded or riveted friction material puck. A typical brake set usually contains 4 pucks 2 inner and 2 outer for one front or rear axle. There are many different types of friction materials depending on the use of the vehicle. |
| What is the function of the Brake Pads? |
| Disc Brake Pads convert kinetic energy to heat energy. Under braking there is a small amount of friction material transferred from the pads to the rotors this helps the rotor and pads stick providing the friction to bring the vehicle to a stop. This material transfer is why you need to break in the pads and rotors. If the pads are not properly broken in they can leave an un even deposit of brake material on the rotors surface resulting in a high runout, Disc Thickness Variation and other problems.
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| What are the different types of Brake Pad? |
| There are many types of pads and pad formulations. These formulations have different characteristics and can vary from soft compounds used for road driving to very hard and aggressive compounds used for racing. The materials and the hardness also contribute to different operating temperatures pads. This is why you should not install racing pads on a road car. Racing pads are harder and work at higher temperatures than pads for road car. The vehicle will not be able to generate enough heat to bring the pads to operating temperatures. Not only will the car not stop properly but the harder friction compound will prematurely |
| Non Asbestos Organic Brake Pads: |
| Organic Disc Brake Pads are made of natural materials and contain less than 10% steel fiber. They also can contain fibers made of rubber, carbon, Kevlar and glass combined with high heat resins. These pads are usually softer and quieter than other brake frictions but they also ware quicker and do not hold up well to higher temperatures. Organic pads work fine on smaller vehicles that do not generate a lot of heat when braking. The stop well at cold temperature but will start to fade under heavy braking conditions. |
| Semi Metallic Brake Pads: |
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Semi Metallic brake pads are found on most vehicles today ranging from small light cars to Heavy Duty Trucks and off road vehicles. They are the most common type of pads because they are usually reasonable price, work well at high temperature, resist fading and provide excellent overall braking performance.
Semi Metallic pads contain 30% to 60% of metallic fibers such as iron, steel and copper they also contain graphite and resin. The metallic fibers help heat transfer and provide better braking performance. They work well at high temperature and resist fading
Semi Metallic Disc brake pads are usually harder and depending on the formulation can make more noise, dust, wear more on the rotors and don’t stop well in cold weather. But not all semi metallic pads are equal. There are many formulations that will outperform some ceramic pads in all aspects such as stopping, fading, noise and dust.
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| Ceramic Brake Pads: |
| Ceramic pads contain ceramic fibers, nonferrous filler materials, bonding agents and may also contain small amounts of metal fibers. They offer excellent braking, noise and ware characteristics. Most ceramic pads work well in a wide range but some other materials work just as well or better.
The name Ceramic pads covers a wide range of friction materials, there are many different types of ceramic pads in the market. Ceramic Pad formulations range from very high content of ceramic fibers (usually for race applications) to formulations that contain a very minimal amount. In some cassis company add some small amounts of Ceramic fibers to their formulation just so that they can name them Ceramic Pads and charge a higher price. Typically good Ceramic pads are higher priced because the materials and manufacturing process is much more expensive than other brake frictions materials. Don’t be fold there are many cheap ceramic pads on the market (usually Made in China) that are noise and don’t last very long before they start to fall apart. |
| What are the difrent types of Brake Pad Construction? |
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| Riveted Brake Pads: |
| Riveted Brake Pad were the most common up until the 90’s. The friction material is molded into pucks and is then riveted on to the backing plate using copper or aluminum rivets. |
| Bonded: |
| Bonding pads are also premolded into pucks and are then attached by using high straight high temperature adhesives.
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| Flash Molded |
| The flash mold process is now very common. The process also uses pre molded friction pucks and then attached to the backing plate by using high heat and pressure. This process uses excessive amounts of resins to help friction material to flow evenly. The extra resin used in this process can cause many problems such as brake fade, noise and excessive material transfer. |
| Positive Mold |
| The "Positive Mold" process is the best way to manufacture quality disc brake pads. It's the process used by all OE manufacturers.
During the "Positive Mold" press curing, the pre-mixed low resin ingredients are placed directly inside the cavity of the cure tooling. Full pressure is exerted on each part by a punch. This guarantees full density is reached on every part. The friction material composition is not compromised by the process and can be tailored for the exact characteristics needed on the vehicle.
This low resin process provides a brake pad with great shear strength and low fade. If you are looking to installing new pads make sure that they are installing pads of the Positive Mold Low Resin type.
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| What is the Brake Pad Coefficient of friction? |
| The Coefficient of Frictions is a measurement used to determine the amount of friction created by moving one object across the other. The Coefficient of Frictions is depended of both surfaces, if the ruffed the surface the higher the coefficient. The value range from 0 to 1.0 Mandated by the US DOT all street legal brake pads sold in the US must contain a 2 letter edge code that specifies the Coefficient of Frictions of the brake pads. The First letter is the grading Coefficient of Frictions of is at 250 degrees Fahrenheit and the second letter is the grading at 600 degrees Fahrenheit. |