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What’s Stopping You? Take Our Deep Dive into Brake System Materials to Find Out

By: · March 29, 2017

-Brakes are the hardest-working but most underappreciated components in any car’s chassis. Their operating temperatures top those of most engine parts, and their working environment includes occasional pothole and puddle dips. Brakes are often your last line of defense prior to a collision.--To show our appreciation for brakes and to better understand how they ward off fender benders and ditch encounters, we visited Brembo USA, located only a few miles from our Ann Arbor, Michigan, headquarters,  for an expert show-and-tell lesson. Brembo is the world’s best known and most respected source of high-performance braking equipment for both original-equipment and aftermarket applications. Our Corvettes, Porsches, and Mercedes-AMGs would be lost without them.--The following photo essay focuses on the materials Brembo uses in its car, truck, and motorcycle calipers and discs. (The terms rotor and disc are used interchangeably for this technology.) Pay attention;  there may be a quiz.-Starting near the top of the technological scale, this carbon-ceramic rotor from the rear of  an Alfa Romeo Giulia Quadrifoglio is an amalgam of several high-performance materials. The main rotor begins as a mix of carbon fibers and phenolic resins baked in a precision mold. After the resin is burned away, the remaining carbon matrix is infiltrated with liquid silicon yielding a tough, heat-resistant, and light brake disc. Following various machining operations including cross-drilling with ultrasonic boring tools, oxidation protection is sprayed onto all surfaces.--The bell at the center of the rotor is stamped or machined from a billet chunk of aluminum, then attached to the rotor with stainless-steel fasteners that allow controlled relative movement between the two parts to accommodate heat-induced expansion. The entire manufacturing process for the finished carbon-ceramic rotor takes a full week versus less than a day for a cast-iron rotor—one reason why carbon-ceramic rotors are often such a pricey option.-This U.S.-made single-piece rotor is a gray iron casting. To encourage airflow and heat rejection, there are radial vents and numerous internal “pillar posts” to support the outer friction plates. A carefully machined center bore accurately locates this rotor on the vehicle’s wheel hub. Supplementing the wheel mounting holes are five additional holes to reduce the rotor’s weight and to allow alternative mounting locations. After all surfaces are machined, a notch is cut in the rotor’s periphery to fine-tune its balance.-Cross-drilling and machining curved slots in a cast-iron rotor serve multiple purposes. In addition to the racier appearance, the holes and slots vent gases released by the brake pads and clear the moisture present during driving on wet roads. The slots perform what’s called a “micro shave” of the pad surface to assure that fresh friction material is always in contact with the rotor. Of course, this accelerates pad wear, one reason why most carmakers think twice about providing slotted surfaces. A zinc-based outer coating minimizes corrosion while the new vehicle is in transit to the customer.-This combination of a solid cast-iron disc and a steel center section saves weight (versus a single-piece cast-iron design) and cost (versus the two-piece design that follows). The two parts are joined together with a combination of crimping and radial locking that requires no fasteners. Mercedes-Benz uses this design on commercial vehicles for which aggressive braking from high speeds is a rarity.-This made-in-America rotor is installed on Chrysler and Dodge vehicles equipped with the Hellcat supercharged V-8. The two-piece design includes a huge cast-iron outer component with a stamped-aluminum center section. The two are joined with stainless-steel six-point star bolt fasteners, nuts, and locating bushings. Surface slotting and pillar post internal construction improve airflow and heat rejection.-Collaboratively developed by Brembo and Ford, this two-piece iron-and-aluminum rotor came from one of the Ford GT racers that finished at the top of the GTLM Pro class last year at the 24 Hours of Le Mans, where the carbon-ceramic brakes fitted to the roadgoing GT are forbidden. Curved internal vanes are used without any cross-drilling. These rotors show extensive cracking in the cast-iron surface, but that doesn’t mean failure is imminent because all the fissures are shallow. In fact, this design was engineered to last a full 24 hours with no service beyond pad replacement. The center section is machined from an aluminum billet.  During a pit stop, the colored paint marks provide a visual indication of the maximum temperature this rotor has experienced.-More exotic and lighter carbon-carbon brake rotors, allowed for LMP1 and LMP2 cars at Le Mans, are also favored in MotoGP (top-line motorcycle road racing) and in Formula 1. Here, the manufacturing process runs three to five months. Long or short carbon fibers are first molded in a preform tool with a resin binder. After infiltration with methane gas, each rotor is cooked at high temperature for a long period (the length of which was not revealed for proprietary reasons). This yields carbon fiber held in a carbon matrix—hence the name “carbon-carbon.” A special paint is applied to resist oxidation. The caliper used with this rotor is a four-piston design machined from a billet of aluminum.-Motorcycles intended for street riding use stainless steel instead of the cast-iron and carbon-ceramic rotors common in the four-wheeled world. One reason is because these brakes are proudly displayed for the entire world to admire, and corroded cast iron fails from an aesthetic standpoint. In addition, the thermal capacity needed to stop a two-wheeler is far lower than what’s experienced in cars, and a cross-drilled stainless-steel disc is quite sufficient for repeated stops from high speeds. The disc shown here, from a Ducati Panigale sport bike, is attached to the front wheel through a stamped-aluminum center hat. Six crimped fasteners and shims provide the desired amount of radial movement to accommodate thermal expansion, thereby reducing noise and vibration. The four-opposed-piston caliper for this application is rigidly mounted to the bike’s fork.-NASCAR short-track racers use Brembo braking equipment to quicken their lap times. This monoblock (single piece) front caliper is machined from an aluminum billet and contains three pistons per side. The arrow indicator helps achieve the proper orientation because these calipers differ side to side. The open windows and ribs in this component dissipate heat. The pads used with this caliper are made of ceramic material bonded to a high-carbon-steel backing plate.-This eight-piston cast-aluminum caliper is designed for use on trucks and large SUVs such as the Mercedes-Benz G-class. Here, the pads consist of a proprietary blend of steel and copper material attached to a steel backing plate. Asbestos, deemed a health hazard, was once commonly used but has been banned from brake friction materials for two decades.-Floating calipers, common in low-performance vehicles, are for the most part beneath Brembo’s dignity, because they don’t provide the stiffness, pedal feel, and thermal stability essential in sports-oriented cars and trucks. Of course, for every rule there’s an exception, exemplified by the Ferrari LaFerrari rear assembly illustrated here. An electrically actuated floating-type parking brake made mostly of cast iron attaches directly to a four-piston aluminum monoblock caliper. Doubling up on function saves weight and eases assembly.-Proving that brakes have earned full boutique status, Brembo introduced a new high-style caliper at the 2016 SEMA show. The six-piston, two-piece design shown here is held together with five bolts and will be sold through GM’s service parts organization for large Chevrolet truck models. While it isn’t intended for off-road racing or performance use, this caliper’s aluminum construction does save a few pounds. Following anodizing, the caliper is painted red for a long-lasting and attractive appearance.-The aluminum monoblock caliper shown here is used on the front wheels of Ford GTs intended for road use. The six opposed-piston bores are machined using sophisticated CNC cutters designed to work within the tight internal confines. The center rib enhances this caliper’s stiffness, and radial mounting holes facilitate a stiff, light attachment to the front suspension knuckle. To simplify manufacturing (a bit), brake fluid flows from the inside to the outside of this caliper via an external steel line.-Thanks for your rapt attention on this fast lap through the Brembo catalog. Your quiz challenge: Name the most common use of steel in braking components. ---(Answer: Motorcycle discs where stainless steel is used to avoid unsightly corrosion.)


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