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More Than Just Brakes!Posted 11/6/2002By Keith Reinhardt
Today's automotive brake system is made up of a combination of perpetually evolving mechanical, hydraulic and electronic components. Given that everything involving the service and repair of the automotive brake system is safety orientated, shop owners, service technicians and educators alike must maintain a constant awareness of current repair trends and safety issues. The following topics seek to identify some of the most recent repair trends and safety issues relating to automotive brake service. Application-Specific Brake Linings To help brake repair facilities meet safety and liability requirements, most brake friction manufacturers are now offering an "application-specific" or "application-engineered" replacement lining. Application-specific linings assure the brake pad installer that even if the lining is fabricated from a material different than original equipment (ceramic-based versus semimetallic) the friction characteristics are equivalent. Therefore, proper pedal feel, braking performance and brake balance is preserved. Today, brake balance is more important than ever since approximately 90 percent of all new vehicles are equipped with an anti-lock brake system (ABS). If aftermarket brake linings are installed that do not closely match the design specifications of the original equipment manufacturer (OEM) brake linings, the front-to-rear brake balance may be altered, changing the threshold of brake lockup. This may cause a detrimental effect on the operation of the ABS system when panic stopping or braking hard on slick road surfaces. Interestingly, according to The Wall Street Journal (March 6, 2002) the Bush administration has suggested it might require vehicle manufacturers to install ABS on all new vehicles. Ceramic Brake Lining Material Although first introduced as far back as 1985 on some new vehicles, mass aftermarket applications for ceramic-based disc brake pads are just now becoming widely available. Approximately 33 percent of all new vehicles, domestic and foreign combined, now have ceramic-based disc brake pads. The newest generation of ceramic brake lining compounds contain no chopped steel fibers or steel wool as found in earlier semimetallic linings, but instead substitute ceramic compounds and copper fibers. These changes provide modern ceramic-based lining materials the capability of handling today's high brake temperatures with less heat fade, faster recovery time, and less wear on both the pads and rotors. Of even more value to brake repair facilities is the ability of ceramic lining compounds to significantly reduce annoying brake noise or squeal, which is the No. 1 consumer complaint relating to brake service. Ceramic compounds dampen noise and move brake pad vibrations to a frequency outside of our human hearing range, 20 Hz through 20,000 Hz. As with earlier disc brake pad designs, some ceramic pad applications may also incorporate other noise-reducing features such as chamfers, slots and insulator shims. One leading aftermarket manufacturer has gone as far as naming its line of ceramic brake pads "Quiet Stop." Another positive characteristic associated with ceramic brake lining materials is the absence of visible brake dust, a feature that any vehicle owner with stylish wheels will appreciate. All brake materials, ceramic included, will produce some brake dust. Earlier semimetallic and organic brake compounds left a brownish black dust on wheels. In comparison, ceramic compounds produce a light-colored dust that is much less noticeable and does not attach itself to wheels. Although an increase in product cost will more than likely be associated with ceramic-based brake linings, their benefits may be worthwhile for consumers. Based on their own durability tests, lining manufacturers say these compounds will outlast most other premium pad materials by a considerable margin. However, aftermarket brake pads with ceramic materials should only be used on those applications where the OEM specified a similar formula. Rotor Service and On-Car Brake Lathes Although not always accepted in today's brake repair facilities, most vehicle manufacturers do not require that disc brake rotors be refinished as part of routine brake service. Ford Motor Co. states in Bulletin No. 99-19-04 that rotors should only be "resurfaced if diagnosis has revealed vibration in steering wheel, seat or pedal while braking. Heavily scored rotors, similar to that caused by linings worn down to the backing plate, should also be turned." General Motors Corp. likewise states in Bulletin No. 00-05-22-002A that brake rotors should only be turned when one of the following rotor surface conditions exist:
Should rotors need service, most original equipment manufacturers (OEMs) highly recommend the use of "on-car" brake rotor turning as a method of eliminating stackup of lateral runout, which is a potential source of brake pulsation. (Lateral stackup is the product of rust/contamination trapped between the hub and rotor mounting surface and rotor or hub high and low spots not properly positioned during assembly.) On-car brake lathes mount either directly to the hub of the car's wheel (see Figure 1), or require the brake caliper to be removed and mounted in its location. At this time, the hub-mount type of on-car brake lathe has been approved by all three domestic automakers and at least one foreign automaker. On-car brake lathes have been gaining in popularity and by today's standards are considered an essential piece of equipment for the modern full service brake repair facility. With these lathes, the so-called "trapped" rotors, which are not easily removed from vehicles, can be quickly and easily serviced. In addition, with an on-car lathe, removable rotors and rotors not requiring wheel bearing service can be refinished faster and with less chance of lateral runout problems. For those facilities without on-car lathes, GM has recently approved a new technology for the correction of lateral runout on new or refinished rotors. This new method is called "Brake Align" (refer to GM Bulletin No. 01-05-23-001). It allows lateral runout to be reduced to .050 mm (0.002 inches) or less by installing a specially selected, tapered correction plate between the rotor and hub. Before the Brake Align correction system is facilitated, the existing rotor must first be machined on a well-maintained bench brake lathe to guarantee smooth, flat and parallel surfaces. It is still not necessary to machine new rotors when using this system. Fluid Service and Brake Bleeding
A somewhat new brake bleeding method finding some popularity among brake repair facilities, especially for those tough-to-bleed brake systems, is called reverse fluid injection (RFI). This bleeding technique involves forcing low pressure (approximately 10 psi.) brake fluid into the bleeder screw up to the master cylinder (see Figure 2). Some technicians have expressed concerns about the possibility of forcing contaminated fluid and debris back upstream into ABS and other brake system components with this method. These concerns are put to ease when you consider that the RFI method should only be performed after the system has been flushed, and that a very low pressure is placed on the fluid during the process, preventing debris from being dislodged and forced upstream. Brake Facility Safety Issues
If a brake drum cannot be easily removed to allow brake cleaning, then it should be carefully pulled back far enough to allow thorough wetting of the brake parts to prevent friction material from becoming airborne during removal. For this particular job, the spray/solvent can method might not be an acceptable procedure since it may not offer the ability to thoroughly wet all brake parts. As professionals, we must keep abreast of new service procedures and products to provide accurate and safe brake service for our clients. As brake systems evolve, so must our service techniques.
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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Almost all vehicle manufacturers and aftermarket brake parts suppliers state that new rotors should not be resurfaced before installation.
Although OEMs are not citing brake fluid as a regularly serviced item, most service technicians recognize that it is not a lifetime fluid due to its hygroscopic nature. Some studies have illustrated that brake fluid typically absorbs approximately 1 percent or more moisture per year of service life. This moisture in the brake fluid subsequently lowers the fluid's boiling point, possibly leading to pedal fade under hard braking conditions. Additionally, brake fluid's heat and chemical activity erode its ability to prevent corrosion. This can lead to abrasive wear within the brake system's components, especially small, sensitive ABS fluid control devices. For these reasons, brake fluid service should be considered essential. Many experts and aftermarket brake parts suppliers recommend flushing and replacing brake fluid every two years or anytime the brakes are being serviced.
Although modifications in brake friction materials have occurred over the last several years, today's technicians are still servicing asbestos brake linings. As always, service to these brake linings can pose a safety hazard if not properly addressed. The U.S. Department of Labor, through the Occupational Safety and Health Administration (OSHA), has identified specific compliance methods for brake repair facilities. Only repair facilities that perform five or more brake jobs per week are required to adopt these procedures to meet OSHA regulations. OSHA lists three "preferred methods" for brake cleaning: the low pressure/recycle method also known as the wet brush method (see Figure 3), the enclosure/high efficiency particulate air filter (HEPA) vacuum method, and the spray/solvent can method.
