The information in this article came from a technical symposium attended by trainers from General Motors, Ford & Chrysler, also Firestone, Goodyear, Big O Tire, Car-X, Merlin, Midas, Monro, Sears, Tuffy, Pep Boys, ProCare and others. The event, was sponsored by Pro-Cut International, a manufacturer of on-car brake lathes. The purpose of this event was to allow aftermarket tech trainers to quiz OEM brake engineers about their recommend brake service procedures, new brake designs and any problems they are experiencing in their shops. Keep in mind that the responses given by the OEM engineers reflect their opinions towards new car dealer warranty service procedures and fixes, not necessary repairs that work for the aftermarket. Also keep in mind that the responses given by the individual engineers are not necessarily the "official" policy of the vehicle manufacturer they represent. In some cases, they expressed their own personal opinions rather than an "approved" service policy (no lawyers were present). It's also interesting to note that the engineers from Ford, General Motors and Chrysler expressed opposite views on several important issues, including procedures for correcting brake pulsation problems caused by rotor lateral runout (GM approves the use of tapered alignment shims behind the rotors, but Ford and Chrysler do not.), the use of a lubricant or anti-corrosion treatment between the brake rotor and hub (Ford said yes, GM said never), and the use of brake pads that contain ceramic fibers (Ford and GM use them but Chrysler does not). Here are my notes from the seminar: General Motors Brake Service Recommendations Presented by Russ Dobson – GM Service Operations, Warren Tech Center BRAKE PULSATION & RUNOUT PROBLEMS Brake pulsation has been a high warranty issue for GM. GM added four new categories to service manual procedures to cover brake rotor replacement (went from 1 page to 16). Is also paying increased labor rate to cover time needed to make measurements and corrections (a few extra tenths of an hour labor). New manual section covers basics of measuring and correcting Lateral Runout (LRO) Correction. NOTE Very important to clean any rust/dirt/corrosion from hub anytime rotor is removed from hub. Cleaning is critical! Must measure assembled lateral runout to see if correction is needed. Must be less than .002 in. If more than .002 runout, may not create a brake pulsation right away but it will appear within few thousand chilometri. If a customer has a brake pulsation, you know you have variation so rotors will have to be resurfaced or replaced. GM says measuring rotor thickness variation is very hard to do accurately in the shop, so why waste time trying to measure it? GM spec for maximum allowable thickness variation in rotors is 0.025 mm (0.001 in.). In the real world, the only things you can measure accurately are rotor thickness and flatness. You can't measure rotor thickness with a high degree of accuracy unless you measure about every couple inches all the way around the rotor. If the rotor pulsates, it has thickness variation and is bad. To measure lateral runout, mount rotor on hub, install special conical washers (J45101-100) on lugs, then install and torque lug nuts to specs. This simulates wheel load on the rotor. Then you can accurately measure runout. Maximum runout will vary according to the vehicle, but on Chevy Malibu should only be 0.04 mm (0.0015 in.) max. Major cause of rotor runout is rust & corrosion between hub and rotor, and improper lug nut torque loading. That's why it is so important to inspect and clean mounting area between hub and rotor. GM has had major runout problems with Malibu ("Warranty problems though the roof"). The car uses small, composite rotors. GM has had difficulty building hub/rotor to .0015 in. or less tolerance at plant. GM has switched to softer pads (number 1417 on pad edge), and tried to tighten hub build tolerances. They are also using a "correction plate" (shim) between the rotor and hub to correct excessive lateral runout in factory and in the field. To correct a rotor runout problem, first try indexing rotor position on hub to reduce total runout. If that doesn't work, can install thin tapered shim (correction plates) between rotor and hub — or turn rotor with on-car lathe. Correction plates: GM says don't reuse old plates, and don't stack plates (one only!). If you install a new rotor, remove and discard the old shim. A new shims should not be needed unless the hub has runout problem or the rotor has been incorrectly machined. After marking high spot on rotor, install shim with notch opposite high spot. GM admits using correction plates does change wheel alignment slightly. GM approves correction plates for cars only (not trucks), and only for problem cars (like the Malibu). Lug nut torque is very important. GM guy says leaving only a single lug nut loose or undertorqued may create as much as .003 in. of lateral runout in the rotor! On-car lathe: GM says turning rotors on the car takes about the same time as measuring/correcting rotor runout with shim procedure. GM does recommend on-car resurfacing to correct runout, but is an expensive technique because of equipment cost. Dealers can decide for themselves whether or not to buy an on-car lathe (not a required tool). GM says it is not necessary to resurface rotors every time pads are replaced. Do not reface new rotors. Latest GM warranty bulletin says .002 in. is maximum lateral runout for rotors. Never use grease or lubricant on lugs, nuts or between mounting surfaces. Dry and clean only. For 2003 model year, GM has changed to a new wheel design with a "flat" hub surface that mounts flush against the rotor and hub. Most GM OEM wheels have a slightly conical mounting surface that helps clamp the rotor against the hub (spring back effect) — but on the Malibu this increases rotor distortion due to design of rotors and hub. By changing to a flat wheel, rotor distortion is reduced — but it also requires very accurate torquing of lug nuts. Technicians must use a torque wrench or torx sticks. ROTOR FINISH SPECIFICATIONS? GM says RA finish on rotors should be 40 RA after turning and sanding. GM says to use sanding block and 150 grit aluminum oxide sandpaper. Sanding enhances surface finish and initial brake performance. Smoother is always better. ROTOR RUSTING? GM rotor rusting is currently a BIG problem. GM removed chromium from rotor alloy to reduce cost — but this has increased rotor rusting in field. GM looking at nitrate coated rotors and gray iron rotor to improve rust resistance. GM has also looked at ceramic rotors but they are way too expensive now. ROTOR REPLACEMENT? GM says it has not completely evaluated effects of replacing composite rotors with solid rotors. Current advice is to replace same with same. CLAMPING BRAKE HOSES? GM says NEVER! Risk of damaging hose too great. ROTOR RESURFACING EQPT. GM recommends using a positive rake bit in lathe because it requires less pressure, enhances flatness and surface finish. Old Ammco 4000 lathe had negative rake. GM did not approve it until Ammco gave them a positive rake. GM also says to use OE bits. Some round bits may not give as good a finish. ROTOR SERVICE SPECS GM moving toward one minimum rotor thickness spec. Not happened yet, but heading in this direction. GM currently has three different specs. Is too confusing now. Minimum machine to thickness spec should include enough thickness to allow for a certain service life after resurfacing. Question is, how much? Discard spec is thickness at which rotor is unsafe and must be replaced. To reduce rotor runout, GM improving plate assembly procedures to tighten tolerances. Goal is .002 in. or less. GM is starting to attach rotors to hubs with fasteners instead of just slipping them on hub. Fasteners hold rotor in plate when wheel is removed and reduce risk of anything getting between rotor and hub. OEM BRAKE TRENDS? Going to larger rotors and pads (needed to meet new FMVSS 135 braking standards). GM won't repeat Malibu "mistake." CHANGING BRAKE FLUID? GM says fluid changes are unnecessary – except for some offshore models that do have a specified change interval. For 2004, new GTO Monaro (Holden) from Australia will have a fluid change recommendation. GM is, however, currently reviewing the FASCAR drip strip method of checking brake fluid. ROTOR NOISE TREATMENTS? GM says is okay and has a product of their own for this purpose. Rotor fin configuration? Some aftermarket rotors use different fin pattern than OEM? Is this okay or not? May affect cooling and heat management. May also affect rotor noise dampening characteristics. Chrysler Brake Service Recommendations Presented by Bill Fedelem, Jerry Balogh & Mike Wiacek FUTURE OF ELECTRONIC BRAKE CONTROL Will see "giant leaps" in new brake technology. Bosch, TRW (Kelsey-Hayes) and Continental Teves developing lot of new hardware. ABS currently available on most Chrysler products. Traction control available on all cars, coming to trucks & SUVs now. Next is stability control (ESP is DaimlerChrysler acronym). Is standard on all Mercedes now. ESP makes a real improvement in vehicle handling and stability for safer driving. Drivers appreciate it more than ABS. Electro-Hydraulic Braking (EHB) will be available in 2003 on some luxury cars. Will replace vacuum booster. Will have accumulator for backup to apply brakes if electronics fail. Booster and master cylinder replaced with pedal simulator and failsafe hydraulic manifold. Electronic brake controls replaced by EHB unit. Will likely require special OEM dealer tools and training to service and fix. By end of decade may see full brake-by-wire systems with electronic calipers. CHRYSLER WHEEL SPEED SENSORS Old tech: variable reluctant magnetic wheel speed sensors New tech: Hall effect "active" speed sensors with integrated circuit. Diagnosis is more complicated. Hard to bench test good or bad. Diagnostics are built…

Fonte: AA1Car.com