Brake Tech: What is a Complete Brake Job?

Transcription

1 Page 1 of 7 Print Close Window Brake Tech: What is a Complete Brake Job? Larry Carley 1/1/2008 Most motorists know brake linings don t last forever. Brake pads and shoes use friction to stop a vehicle, so every time the brakes are applied the linings experience wear. After so many stops, the linings wear out. The rate at which the linings wear out depends on the frequency of use, how hard the brakes are being applied, the temperature of the linings and the wear characteristics of the friction material itself. Larger, heavier trucks and SUVs typically wear out their brakes faster than smaller, lighter cars. Stop-and-go city driving obviously wears the linings down faster than highway driving. So does aggressive driving. Consequently, a set of brake linings on one vehicle might only last 25,000 to 30,000 miles when on a different vehicle they might go 50,000 or 60,000 miles. As a rule, most brake pads and shoes should be replaced when the thickness of the friction material is worn down to minimum specifications (typically less than 1/8th inch of lining thickness) or when the surface of the pads or shoes is worn down flush with the tops of the rivet heads (riveted linings). Some brake pads have built-in wear indicators that generate a metallic scraping noise when the pads are worn out and need to be replaced.

2 Page 2 of 7 SELLING THE BRAKE JOB OK, the linings are worn and need to be replaced. Now what? Do you sell your customer a quickie hang and turn brake job (just replace the pads and turn the rotors), or do you sell them a complete brake job? Brake linings and other parts that are obviously worn out, broken or leaking should always be replaced. But what about parts that are marginal or appear to be OK? Should drum brake hardware always be replaced, or can it be reused? Should calipers or wheel cylinders always be rebuilt or replaced if they are not leaking, or should you leave them alone? What about replacing the master cylinder in a high mileage vehicle? Should you always flush the brake system and refill it with fresh fluid? Some people might think you re trying to rip them off if you recommend replacing parts that are still working, but are near the end of their service life. This is a hot button issue with consumer advocates and government regulators because they may see it as an attempt to sell unnecessary parts and services. Nobody wants to pay for parts or services they may not need, so in some states (California) there are strict regulations covering the replacement of brake components. The rules say when you can and cannot replace various brake system components based on wear or condition. A less draconian approach has been taken by the Motorist Assurance Program (MAP) to help technicians, service advisors and shop owners do a better job of selling brake repairs. MAP s voluntary repair guidelines cover the brake inspection process and tell you when brake repairs are truly necessary, or when brake repairs can be recommended to improve braking performance or to restore the brakes to like-new condition. Many times the person doing the brake inspection has to make a judgment call as to whether or not something should be replaced which means their decision is often a judgment call. For years, industry accepted practice was the criteria by which many technicians based their decisions. The trouble with this approach is that everybody has their own ideas about when certain brake parts should be replaced and why. Take brake linings, for example. Should the linings be replaced only when they are at or below minimum thickness (as defined by the vehicle manufacturer) or is it OK to replace them if they are still above minimum thickness, but are getting thin? This is a call that many technicians have to make when doing a brake job. Though it might not be absolutely necessary to replace the rear linings right now, doing so could save the customer the cost and inconvenience of having to replace them later. The best answer in this situation would be to discuss the situation with the customer and let them make the final call. WEAR ISSUES One of the major issues with selling customers a complete brake job is that the components in the brake system do not wear at the same rate. The front brakes typically

3 Page 3 of 7 wear two to three times faster than the rear brakes. Consequently, it may not be necessary to replace the rear linings until the second or third set of front pads have been replaced. Time, mileage and the operating environment are all factors that affect the service life of parts in the brake system. Brake fluid is hygroscopic and absorbs moisture over time. As moisture accumulates in the fluid, it increases the risk of internal corrosion inside the calipers, wheel cylinders, steel brake lines, master cylinder and ABS solenoid valves. Because of this, it s not unusual to find corrosion-related failures in these components in high mileage vehicles that are operated in wet climates. Recommending a fluid flush for preventive maintenance would therefore be a valid suggestion. And if the fluid is more than three or four years old, changing it when the linings are replaced or other brake work is performed would be a good idea. Many technicians recommend rebuilding or replacing calipers and wheel cylinders as part of a complete brake job and with good reason. Over time, rubber seals on caliper and wheel cylinder pistons harden and lose elasticity. This may cause the seal to leak. Corrosion inside the piston bore can also accelerate seal wear. Pushing the caliper pistons back in their bores also causes the seals to rub against an area on the piston that may have become corroded and rough, which can accelerate seal wear, too. So even if the caliper or wheel cylinder is not leaking when you replace the linings, eventually it will leak. Since there s no way to know how long it will be before the brakes are serviced again, many technicians think that rebuilding or replacing these parts to restore the system to like-new condition reduces the risk of brake-related problems down the road and they are right. The point here is components in the brake system wear at different rates which cannot be predicted by time or mileage alone. That s why a thorough inspection of the entire brake system is so important any time brake work is needed, or any time the brakes are experiencing a problem (noise, pulling, dragging, soft pedal, etc.). A complete brake job, therefore, is (1) inspecting the entire brake system to determine the condition of all its major components so (2) you can recommend any repairs that are necessary to restore the brakes to proper operating condition for safe driving. THE COMPLETE JOB The brakes are the most important safety system on a vehicle, so a complete brake job should cover every aspect of the system. It should start with a thorough visual inspection of the entire brake system. This includes measuring lining thickness front and rear (which will require pulling BOTH rear drums), the condition of the lines, hoses, calipers and wheel cylinders, the appearance and condition of the brake fluid, checking pedal feel and travel, and the brake and ABS warning lights (lights should come on then go out when the ignition is turned on). Only after the inspection has been completed should any repair recommendations be made. The ABS system is often overlooked when doing brake work on late model cars. If the ABS warning light is on, there is a fault that needs to be investigated. This will require plugging a scan tool into the vehicle s diagnostic connector to read out the diagnostic trouble code(s). If the light is out (and is not burned out), it s usually safe to assume the ABS system is functioning properly unless the vehicle has been experiencing any unusual brake problems or the ABS system has been kicking in unnecessarily when

4 Page 4 of 7 braking normally on dry pavement. There may be an issue that will require additional diagnosis. A test drive is an excellent way to evaluate overall brake performance. But unfortunately many techs don t have the time to test drive every vehicle they work on. Because of this, problems may be overlooked that may cause a comeback later. WHEN REPAIRS ARE MADE Once the entire brake system has been inspected, a recommendation to the vehicle s owner can be made as to what parts needs to be replaced. In most instances, a complete brake job will include the following: New linings front and rear. Resurfacing both rotors and drums (or replacing them if worn, cracked or hard spots are found). Replacing drum hardware and caliper bushings/pins/sleeves. Rebuilding or replacing calipers and wheel cylinders (depending on mileage and condition). Maybe replacing some brake hoses and/or the master cylinder (if leaks or problems are found). Test the brake fluid and, if necessary, flush the brake fluid and bleed all the lines. Inspecting wheel bearings (repacking on older vehicles). Lubricating all critical areas such as caliper slides and shoe pads with high temperature brake lubricant. Checking & adjusting the parking brake. Checking the ABS system for any fault codes, or replacing any faulty ABS components as needed (wheel speed sensors, hydraulic modulator, accumulator, pump or relay). THE PARTS LIST When brake linings are replaced, always follow your friction supplier s guidelines. As a rule, linings should be replaced with ones made of the same basic type of material as the original linings (or better). The best advice here is to recommend premium grade linings as opposed to standard or economy grade linings. Premium linings will usually give your customer the best performance, longevity and overall value. If you are installing a loaded caliper assembly on one side of a vehicle only, make sure the pads have the same approximate friction characteristics as the ones on the opposite side. If a different grade of friction material is used, it can increase the potential for a brake pull.

5 Page 5 of 7 Unless the rotors and drums are in near perfect condition (no scoring, minimal runout, etc.), resurfacing should be considered a must to restore an optimum friction surface. Rotors should be resurfaced to OEM specifications. If rotors are worn to minimum thickness, or can t be resurfaced without exceeding the minimum or discard specs, they must be replaced. Rotors should also be replaced if they are cracked, have hard spots or are severely corroded. If you are refinishing the rotors, it is a good idea to apply a non-directional finish to the rotor. The engineering behind a nondirectional finish is that the scratches on the surface go in various directions, so there is less change of pad vibration and noise. The nondirectional finish doesn t last forever (maybe a few hundred to a few thousand miles of driving depending on brake usage), but it lasts long enough for the new pads to seat and to keep the customer from noticing any noise from the newly installed pads. Nondirectional rotor finishes can be applied a number of ways. A nondirectional finish can be applied with an abrasive disk in a drill or a special rotor refinishing brush. These abrasive tools knocks off the sharp peaks on the surface of the rotor. Some of these tools are manufactured by companies that produce surface finishing tools for engine builders. The disc rotor should be mounted on a brake lathe and rotated between 125 and 210 RPM. The hone tool should be chucked securely in a variable-speed electric drill motor or low speed air drill. The hone tool should rotate RPM. Bring the tool into contact with the rotating rotor at a slight angle and work in towards the center and out to the edge of the rotor face. Light, uniform pressure is used. When the tool is used dry, it should be worked for 15 to 20 seconds at a time. Do not overheat by dwelling for longer periods of time seconds clockwise and 5-10 seconds counterclockwise should produce the desired finish. And don t forget to wash off the rotors when you re done. New rotors, either OEM or aftermarket, are supposed to be finished to specifications and ready to install out of the box. There should be no reason to give them a clean up cut. If they do, you need to find a different rotor supplier. A recent Babcox survey found that 35% of our readers are still machining brand new rotors before they install the rotors on their customer s vehicles. Every rotor manufacturer we have ever spoken to says this practice is NOT necessary, and is counterproductive because (1) it shortens rotor life, (2) may leave a rougher finish on the rotors than the factory finish and (3) may cut runout into the rotors. Drums If a drum is cracked, has hard spots, is bell-mouthed, or the inside diameter exceeds maximum specs or a drum can t be resurfaced without exceeding the limit, it must be replaced. Also, both drums should have about the same amount of wear. If the difference in wear is greater than about.040

6 Page 6 of 7 inches, both drums (or rotors) should be replaced even if only one is at or near the discard limit. As for drum hardware (self-adjusters, return springs, shoe springs, etc.) and disc hardware (caliper slide pins, bolts, bushings, sleeves, etc.), anything that is obviously worn, damaged or badly corroded should always be replaced. If a return spring or shoe spring is stretched or discolored, it has probably suffered heat damage and must be replaced. But many brake experts say it s a good idea to replace springs anyway when doing a complete brake job regardless of the spring s appearance to assure like-new brake performance and to minimize the chance of a comeback. The cost of new springs and other hardware is only a small portion of a complete brake job. Yet it can save you many dollars in lost labor revenue if you end up having to do the job over because you reused old hardware and it failed. The MAP guidelines say it is not necessary to rebuild or replace calipers or wheel cylinders unless they are leaking, cracked or damaged. But as we said earlier, many experts believe replacing or rebuilding these components on high mileage vehicles is well worth the extra cost to minimize the risk of future problems. As for brake fluid, every brake job (complete or not) should include testing the brake fluid. Surveys have found that half of all cars and light trucks that are 10 or more years old have never had their brake fluid changed! You can t really judge the condition of the brake fluid by its appearance. Brake fluid may darken as it becomes contaminated with moisture, but some fluid does not. The most accurate way to check the condition of the fluid is to use an electronic tester that boils a small sample of fluid, or to use chemical test strips that react to the corrosion inhibitors and trace copper in the fluid. Tests have shown that after only a year of service, the brake fluid in the average vehicle can contain as much as 2% water. After 18 months, the level of contamination can reach 3%, and continue to climb to as much as 8% or more as time goes on. As for the ABS system, no parts should have to be replaced unless something isn t working properly. Wheel speed sensors can sometimes give bad readings if their magnetic tip becomes contaminated with metallic debris from the brakes. A simple cleaning may be all that s needed to eliminate the problem. A major ABS problem such as a failed modulator or control module, on the other hand, will be a major expense to replace. A complete brake job, therefore, should be one that completely eliminates any preexisting problems and restores the brakes to like-new condition. There s no substitute for a complete job. If it isn t perfect, it isn t complete. Where Does the Small Independent Shop Fit...? Is MAP relevant to independent shop owners and automotive technicians?

7 Page 7 of 7 That s an increasingly common question from those who look over MAP s member list and see the names of large chains. MAP is an inclusive organization. It seeks the involvement of all firms in the automotive parts and repair industry, regardless of size. MAP is also representative of a trend affecting a variety of industries and professions responding to problems through constructive collective action. Some people in the business might be offended at the notion that anyone would think they re not trustworthy. Maybe that other shop down the street, or a couple of the big chains that have had problems. But not me! My customers know me. And more importantly, I know my customers and what s best for them. This refrain often rings hollow. Perfection eludes even the best companies and organizations. Without uniform guidelines and some basic standards, how will anyone consumer, shop owner, technician, retail manager, government regulator know what criteria to use in evaluating levels of performance? If each company makes up its own standards, the consumer gets widely different treatment and advice, not to mention confused. When more and more consumers get more and more upset about what they see as an overall lack of uniformly reliable treatment by any variety of repair shops, what do they do? They complain. Loudly. And government agencies charged with the responsibility of consumer protection step in and impose a one-size-fits-all regulation. MAP s Uniform Inspection and Communication Standards do reflect the reality repair shops, both large and small, have to face because they have been developed by the car manufacturers and automotive repair companies themselves. Now, right here is where the small shop owner or technician might raise a hand and shout Whoa! Those were developed by the Big Guys but what about me? Actually, the big guys were only part of the group. Small shops, represented by members of FAQT, state ASA chapters, independent dealers/franchisees, and technical trainers from parts and equipment suppliers (the same ones that supply both the large and the small firms), took part in the uniform inspection guidelines development sessions. Regulators in many states are expanding their horizons. While publicity and corporate deep pockets motivate them to go after the larger firms, the regulations that result (including the trend toward licensing and minimum training standards) affect all shops operating in the area. Add to that the notion that strict adherence to MAP s Standards of Service would have saved many of these firms the embarrassment (and a few dollars!), one can see that participation in the Motorist Assurance Program benefits everyone no matter how big or little they might be. Brake and Front End Copyright 2010 Brake and Front End All Rights Reserved.