posted 12-08-2009 09:36 PM                  

How many miles before you need to replace the rear rotors?

posted 12-08-2009 10:17 PM                  

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posted 12-08-2009 11:42 PM                  

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posted 12-09-2009 08:08 AM                  

quote:

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Originally posted by Howard:
Why can't they be turned?

How many miles before you need to replace the rear rotors?

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One of my rear rotors got damaged and I had it turned down by a friend who is a master machinist... next to the " do not turn down " stamp that is right on the rotor they have the minimum spec for thickness stamped on the rotor itself. After turning down it still was thicker than the min spec. The Aluminum/cermic composite material that the rotor is manufactured from is so abrasive it ruined 2 carbide bits, so my buddy used a diamond bit to get it finished.. Brakes work perfect now... I would suggest that the rear pads be replaced every 30,000 miles to avoid rotor damage. The stock pads did not have a squeal bar on them so when the pad is gone you get no warning.

posted 12-09-2009 06:40 PM                  

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posted 12-09-2009 07:19 PM                  

quote:

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Originally posted by xtreme prowler:
They also stamped a minimum thickness on them for a reason, even after being trimmed down they still exceed the stamped dimension.. that is good enough for me... its all what the owner is comfortable with..

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Same thing with mine and I had to agree with the guy that did the work that if he destroyed the rotor he would not be liable.

posted 12-11-2009 09:55 PM                  

Proper torque on lug nuts is very important for three reasons. One is to keep the lug nuts from loosening up and the wheel coming loose, another is to prevent distortion of the brake rotor behind the wheel, and a third is to prevent broken studs. A torque wrench should be used for final tightening of the lug nuts, and the nuts should always be torqued to the recommended specifications.

CAUTION: Torque specifications for lug nuts are always for CLEANand DRY studs and lug nuts. That means no oil, no grease, no anti-seize and no lubricants of any kind. Any of these products will reduce the friction between the threads. This may seem like a good thing to prevent rust and frozen lug nuts, but the reduction in friction means a much higher percentage of the applied torque (up to 25% or more) will go toward loading the lug nuts. The end result may be brake rotor distortion or broken studs!

posted 12-11-2009 09:57 PM                  

The new Safety Standard that Affinia seeks from NHTSA would require all rotors sold in the United States to meet minimum performance standards for structural strength and crack-resistance under rigorous laboratory testing. No such mandatory standard exists in the U.S. today, although rotors are a critical component of a vehicle's most important safety feature, its brake system.

The proposed rule would also for the first time require rotors to be stamped with identifying markings, including a "DOT" (U.S. Department of Transportation) symbol representing the manufacturer's certification that the part meets the new standard.

Until recently, manufacturers of replacement brake parts consistently designed and built their products to match the design specifications and to meet or exceed the performance and durability of the Original Equipment parts that they were meant to replace. Meeting or exceeding OE specifications thus came to be understood by consumers and auto technicians alike as the de facto standard for replacement brake parts.

Unfortunately, within the last year and a half, a number of companies have been importing and distributing aftermarket brake rotors that are lighter, thinner and cheaper than their OE counterparts. Affinia says it also has identified numerous instances in which importers or distributors of lightweight rotors have falsely asserted in advertising or on their Internet sites that the rotors meet OE specifications and performance levels. The end users of these rotors ( retail do-it-yourself customers and technicians who work in vehicle repair shops) have no way of knowing that such assertions are not accurate. Thus, they often will select a replacement rotor based on price, on the assumption that all replacement rotors provide an adequate level of performance, durability and safety.

Affinia says it believes that the only appropriate remedy for this significant public-safety risk is a federal standard that all rotors must meet. Over the years, the automotive industries of North America and Europe have developed separate, but roughly comparable, laboratory testing procedures and criteria for rating the strength and crack-resistance of brake rotors. Affinia would in general prefer adoption of the stricter European criteria, but believes that even adoption of the domestic standards would be welcome because, as the company said in its petition to NHTSA, they "would assure that the worst offenders among lightweight rotors could no longer be sold in this country."

A link to the petition can be found at the Affinia Web site: www.affiniagroup.com.

posted 12-11-2009 09:58 PM                  

For more information about the dangers of thin rotors, visit BadBrakes.net.

posted 12-11-2009 10:03 PM                  

COMPOSITE ROTORS SAVE WEIGHT

This type of rotor derived its name from the fact that it combined a stamped steel center hat with a cast iron rotor. Thus, it was a composite of two different materials. The new design proved to be about 20 percent lighter than a conventional one-piece cast rotor and saved up to a couple of pounds per rotor.

The composite design also allowed the rotor disc on some applications to be cast out of a special "dampened" gray cast iron for added noise suppression (dampened cost iron is not structurally suited for use in a one-piece cast rotor).

Some of these rotors also featured redesigned cooling fins for better heat management. Some were also directional for use on either the left or right side of the vehicle. Directional rotors are not interchangeable side-to-side because reversing the direction of rotation changes the cooling characteristics of the rotor.

COMPOSITE BRAKE ROTOR APPLICATIONS

Some of the earliest applications for composite rotors were the 1982 Lincoln Continental, 1984 Ford Mustang SVO, 1987 Ford Thunderbird Turbo Coupe, and 1988 Ford Taurus and General Motors front-wheel drive "W" body cars (Buick Regal, Oldsmobile Cutlass Supreme and Pontiac Grand Prix). Since then, the number of vehicle applications has continued to grow.

SERVICE PRECAUTIONS
As the vehicles with composite rotors accumulated mileage and came out of warranty, the aftermarket discovered that composite rotors required some special service procedures. Because the stamped steel center hat is not as thick nor or rigid as that in a one-piece casting, the center hat on a composite rotor must be fully supported with special adapters or oversized bell caps when the rotor is resurfaced on a brake lathe. The other alternative is to bolt the rotor to the hub (with the lug nuts reversed to provide better support and to prevent deforming the center hat) and to then resurface the rotor with an on-car lathe.

If a composite rotor is not supported properly, it can wobble and flex creating runout and surface finish problems. Both sides of the center hat must also be clean and rust-free for the rotor to turn true.

ROTOR RECALLS

Some of the early composite rotors experienced corrosion problems and were recalled for replacement. Ford switched some of its models back to conventional one-piece cast rotors for awhile, and issued a service bulletin (#91-8-9) saying it was okay to replace composite rotors on the 1986 to 91 Taurus and 1988-91 Continental with one-piece cast rotors (P/N F10Y-1125-8). The corrosion problem is mostly history now because the OEMs now apply a protective coating to the stamped steel center of the rotor to inhibit rust. Aftermarket composite rotors typically use stainless steel for the center section to prevent rust, and the circumference of the center section is also dovetailed (notched) for increased strength where it mates with the rotor.

Vibration problems were also blamed on the design of the composite rotor. But the underlaying cause more often than not turned out to be improperly torqued lug nuts. Any rotor can warp if the loading on the lug nuts is not even. That is why an impact wrench should never be used to tighten lug nuts, unless it is used with a torque-limiting socket. Otherwise, a properly calibrated torque wrench should be used to tighten the lug nuts in a star or cross-pattern sequence.

REPLACE ROTOR
When worn or damaged composite rotors need to be replaced, be careful not to intermix rotor types side-to-side. Rotors should always be the same type on both sides. Replacing a composite rotor on only one side with a cast rotor may create a brake pull. So do not replace a composite rotor on one side of a vehicle with a cast rotor unless the rotors on both sides are being replaced.

Cast replacement rotors for vehicles that were originally equipped with composite rotors are available from various aftermarket suppliers. But other aftermarket suppliers recommend against substituting one type of rotor for another because the cross-section of the center hat on a cast rotor is significantly thicker than the stamped steel center hat on a composite rotor.

The difference may range from 1/8 to 1/4 inch or more depending on the application. This may not sound like much, but it does reposition the wheel slightly further out on the hub. This adds positive steering offset and alters the scrub radius of the steering geometry. The amount of change is not great, but neither is the amount of scrub radius that is designed into many vehicles. Scrub radius affects steering feel, steering effort and steering feedback. It also plays a role in the way braking and engine torque affect steering.

The change created by replacing a composite rotor with a one-piece cast rotor may be enough to alter the scrub radius from negative (which is the case on many front-wheel drive cars) to zero or positive offset. This, in turn, may create a noticeable difference in the way the steering feels and reacts, especially on cars with rack & pinion steering that are especially sensitive to steering feedback.

There is also a concern that substituting a thicker cast rotor reduces the overall length of the lug studs, which reduces the number of threads available for the lug nuts to retain the wheels (especially on thicker alloy wheels).

Suppliers who subscribe to the "replace same with same" philosophy say you are apt to encounter far fewer problems when you install replacement parts that are the same design and function as the original. Those who do not subscribe to this philosophy say there is often room for improvement over the OEM design.

posted 12-11-2009 10:07 PM                  

Anybody who works on brakes knows what brake rotors do. They provide a friction surface for the disc brake pads to rub against when the brakes are applied. The friction created by the pads rubbing against the rotor generates heat and brings the vehicle to a stop.

The underlying scientific principle here is that friction converts motion into heat, a LOT of heat! The amount of heat that is generated depends on the speed and weight of the vehicle, and how hard the brakes are applied.

A large, heavy vehicle, like a Chevy Suburban, will obviously generate more heat when braking than a Toyota Echo if both vehicles brake from the same speed. But the little Toyota may produce more heat than the big Suburban if the braking speeds are different, say 60 mph for the Toyota and 20 mph for the Suburban. Speed multiplies the effect of weight and creates momentum (also called "inertia" or "kinetic energy").

HOW IT ALL STARTED
Over three hundred years ago, a guy sitting under an apple tree in England made a startling observation that was to change history. As the story goes, an apple fell out of the tree and bonked him on the head. This got him to thinking about the nature of gravity and motion. Since he was no ordinary bumpkin, he soon formulated some basic rules about the way objects behave when in motion.

One of the "laws of motion" he came up with says that any object in motion stays in motion unless acted upon by an outside force. Though this seems pretty obvious to us today, at the time it was a scientific breakthrough because nobody up to that point in history had figured out a way to express the concept mathematically. He soon developed formulas that could accurately predict the exact amount of force needed to accelerate an object of a given size (mass) to a given speed, or conversely how much force it would take to stop an object of a given mass traveling at a given speed. His name was Isaac Newton.

Newtons laws of motion and the formulas he developed became the foundation of modern physics and engineering. The guy even invented a new branch of mathematics called calculus so automotive engineers would someday have the tools to analyze and evaluate braking performance.

BRAKE HORSEPOWER & HEAT
OK, we have explained how brakes produce friction, and friction produces heat, and this is what brings a vehicle to a stop. But we have not explained how much heat is actually produced.

Think of heat as a form of energy or power. A more familiar term is "horsepower." We all know what horsepower is, right? It is the stuff that spins the crankshaft when fuel is burned inside an engine. Combustion produces heat, and heat pushes the pistons that make the crankshaft go around. One horsepower is equal to 33,000 pounds-feet of torque per minute, or 550 pounds-feet per second.

We measure an engines horsepower output by hooking it up to a dyno and seeing how much force it can exert against the resistance created by the dyno. In effect, the dyno acts like a giant brake, so the engines power output is sometimes called its "brake" horsepower output.

By the same token, we can also measure how much horsepower a vehicles brakes must absorb when bringing the vehicle to a stop from a given speed. This is also called "brake" horsepower, but in this case it refers to the brake system, not the engine.

The brake systems on vehicles must be capable of absorbing a lot more horsepower than the engine typically produces because the heat (power) that is generated when braking occurs over a short period of time. Thus, a small car might only need 100 horsepower from the engine to accelerate from zero to a speed of 60 mph. If the driver slams on the brakes and comes to a screeching halt, the brakes have to absorb all the momentum in a much shorter period of time. This multiples the amount of horsepower that must be absorbed, as much as six times depending on the stopping distance. So a panic stop from 60 mph might require the brakes to absorb the equivalent of up to 600 horsepower!

Do not worry about the math because it depends on the speed and mass of the vehicle and the stopping distance. The important point is the brakes often have to absorb a great deal of heat in a very short period of time.

How much heat, you ask? Using more math, units of horsepower can be converted into units of heat energy called BTUs (British Thermal Units). One BTU is the amount of heat it takes to raise one pound of water one degree Fahrenheit.

If you multiply horsepower by the proper conversion factor, you discover that one horsepower generates 42.4 BTUs of heat per minute. If stopping a 4,000 lb. vehicle from 60 mph in roughly 150 feet requires 600 horsepower of force, it is the equivalent of 25,440 BTUs of heat, which is enough heat to raise 15 gallons of water from zero degrees to boiling! No wonder the brakes get so hot.

One thing all brake manufacturers monitor very closely when testing and evaluating pads and rotors is the temperature of the brakes. Every time the brakes are applied, the pads and rotors generate heat that must be absorbed and dissipated. A quick stop from 60 mph can easily push the rotor temperature up 150 or more degrees. Several hard stops in quick succession can push brake temperatures into the 600, 700 or even 800 degree range. Remember, the heavier the vehicle, the more heat it creates when it brakes.

Riding the brakes down a steep mountain road or repeated hard brake applications can produce so much heat the brakes begin to fade.

BRAKE FADE
When brake temperatures get too high, the pads and rotors are no longer able to absorb any more heat and lose their ability to create any additional friction. As the driver presses harder and harder on the brake pedal, he feels less and less response from his overheated brakes. Eventually, he loses his brakes altogether.

All brakes will fade beyond a certain temperature. Semi-metallic linings can usually take more heat than nonasbestos organic or low-met linings. Vented rotors can dissipate heat more rapidly than nonvented solid rotors. Thus, high performance cars and heavier vehicles often have vented rotors and semi-metallic front brake pads to handle high brake temperatures. But if the brakes get hot enough, even the best ones will fade.

DISC BRAKE ROTOR
Now that we have covered some of the physics of braking and the effects of friction and heat on the brake system, lets look at the rotors role in all of this. As we said earlier, the rotor's job is to provide a friction surface, and to absorb and dissipate heat.

Big rotors can obviously handle more heat than small rotors. But many cars today have downsized rotors to reduce weight. Consequently, the brakes run hotter and require better rotor cooling to keep brake temperatures within safe limits.

Anybody who works on brakes for a living knows that rotors can cause a lot of brake problems. Uneven rotor wear (which may be due to excessive rotor runout or rotor distortion) often produces variations in thickness that can be felt as pedal pulsations when the brakes are applied. The condition usually worsens as the rotors continue to wear, eventually requiring the rotors to be resurfaced or replaced.

Rotors can also develop hard spots that contribute to pedal pulsations and variations in thickness. Hard spots may be the result of poor quality castings or from excessive heat that causes changes in the metallurgy of the rotors. A sticky caliper or dragging brake may make the rotor run hot and increase the risk of hard spots forming. Hard spots can often be seen as discolored patches on the face of the rotor. Resurfacing the rotor is only a temporary fix because the hard spot usually extends well below the surface and usually returns as a pedal pulsation within a few thousand miles. That is why most brake experts replace rotors that have developed hard spots.

Cracks are another concern with rotors. Cracks can form as a result of poor metallurgy in the rotor (too hard and too brittle because the rotor was allowed to cool too quickly during the casting process), and from excessive heat. Some minor surface cracking is tolerable and can often be removed by resurfacing, but large cracks or deep cracks weaken the rotor and increase the risk of catastrophic failure. So cracked rotors should always be replaced.

ROTOR METALLURGY
The metallurgical properties of a rotor determines its strength, noise, wear and braking characteristics. The casting process must be carefully controlled to produce a high quality rotor. You cannot just dump molten iron into a mold and hope for the best. The rate at which the iron cools in the mold must be closely monitored to achieve the correct tensile strength, hardness and microstructure.

When iron cools, the carbon atoms that are mixed in with it form small flakes of graphite which help dampen and quiet noise. If the iron cools too quickly, the particles of graphite do not have as much time to form and are much smaller in size, which makes for a noisy rotor.

The rate of cooling also affects the hardness of a rotor. If a rotor is too hard, it will increase pad wear and noise. Hard rotors are also more likely to crack from thermal stress. If a rotor is too soft, it will wear too quickly and may wear unevenly increasing the risk of pedal pulsation and runout problems.

The composition of the iron must also be closely controlled during the casting process to keep out impurities that may form "inclusions" and hard spots. One rotor manufacturer says they sample the molten iron every 15 seconds to make sure the composition is correct. The molten metal is also poured through ceramic filters that trap contaminants. Even the sand that is used to make the molds is specially treated to control moisture content. This helps keep the sand in place and prevents core shifts that can affect porosity, dimensional accuracy and balance.

The grade of cast iron that is used in a rotor may even be changed to suit a particular application. One aftermarket rotor manufacturer uses a special grade of "dampened iron" to make replacement rotors for 1997-2002 Chevrolet Malibu and its sister vehicles (Olds Alero, Olds Cutlass and Pontiac Grand Am). In this case, the original OEM rotors turned out to be too noisy so General Motors switched to a dampened grade of iron to cure the problem.

ROTOR COOLING RIBS
Vehicle manufacturers use a wide variety of different cooling rib configurations in their rotors. They do this to optimize cooling for different vehicle applications. So even though the brakes may appear to be identical on two different models, one may require increased cooling because the vehicle is heavier, has a more powerful engine, has less airflow around the brakes, etc.

Some aftermarket rotor manufacturers use the same rib design and configuration as the OEM rotors, while others do not. Some change the rib design to simplify the casting process or to reduce the number of different rotor SKUs in their product lines.

The OEMs currently use almost 70 different rib configurations in their rotors. Some ribs are straight, some are curved and some are even segmented. Some rotors are directional and some are not. Some rotors have evenly spaced ribs while others do not. Some ribs radiate outward from the center and others go every which way.

One reason why they use so many different rib patterns is to maximize cooling and to reduce harmonics that contribute to brake squeal. Changing the rib design changes the airflow, cooling and noise characteristics of the rotor, which may make things better or worse depending on the application. That is why some aftermarket rotor manufacturers use the same basic design as the original, while others stick with more traditional venting.

One brake manufacturer showed us a cutaway of an offshore "economy" rotor for a particular vehicle that had 32 ribs. The OEM rotor, by comparison, had 37 ribs and provided up to eight percent better cooling than the economy rotor when tested in the laboratory. And because the OEM rib design ran cooler, pad life was 28 percent longer than the economy rotor.

Another aftermarket brake manufacturer showed us test results that proved their rib design improves cooling and makes their rotor three times quieter than a competitive rotor. The recorded sound levels showed noise as high as 85 decibels screaming out of the Brand X economy rotor compared to only 40 to 50 decibels from their own "premium" quality rotor.

ROTOR HEAT DAM
A heat dam is often machined into the area between the friction surface and hat on most rotors. The dam is a thinner section of metal that reduces heat transfer from the rotor surface to the hat. This protects the wheel hub and bearings from the heat and also allows the rotor to flex when it gets hot to reduce the risk of warping and cracking.

If a rotor manufacturer cuts corners and eliminates the heat dam, heat can travel more easily to the hub and wheel bearings and increase the risk of bearing failure. The rotor may also be more prone to cracking under high heat conditions.

ROTOR SURFACE FINISH
We will finish up with a few comments about surface finish. Smoother is always better because it affects the coefficient of friction, noise, pad seating, pad break-in and wear. As a rule, most new OEM and quality aftermarket rotors have a finish somewhere between 30 and 60 inches RA (roughness average) with many falling in the 40 to 50 RA range. It is unlikely you are going to improve this any by "cleaning up the rotors" on a bench lathe prior to installing them. In fact, you may make the finish worse if you cut the rotors too quickly or use bits that are dull.

New rotors should always be installed "as is", and indexed on the vehicle with a dial indicator to minimize runout. As a general rule, there should be no more than .003 inches of rotor runout on most cars and trucks, but some cars cannot tolerate any more than .0015 inches of runout. Few technicians take the time to do this, but if they did they had probably see fewer comebacks because of pedal pulsation complaints.

posted 12-11-2009 10:27 PM                  

Brake problems usually indicate the need for certain repairs or replacement parts, so here is a quick review of some common fixes:

LOW BRAKE FLUID Usually indicates a leak in the brake system which poses a serious safety hazard. The calipers, wheel cylinders, brake hoses and lines, and master cylinder all need to be inspected. If a leak is found, the defective component must be replaced or rebuilt. The vehicle should not be driven until the repairs can be made because a leak may lead to brake failure.

LOW BRAKE PEDAL Can result if shoe adjusters on drum brakes stick and fail to compensate for normal lining wear. Adjusting them may restore a full pedal, but unless the adjusters are cleaned or replaced the problem will return as the linings wear. Other causes include worn brake linings or a fluid leak.

SPONGY OR SOFT BRAKE PEDAL Means there is air in the brake system either as a result of improper bleeding, fluid loss or a very low fluid level. The cure is to bleed the brakes using the sequence recommended for the specific vehicle. Another possible cause is a rubber brake hose that is "ballooning" when the brakes are applied.

EXCESSIVE BRAKE PEDAL TRAVEL Possible causes include worn brake linings, misadjusted drum brakes, and air in the brake lines. Potentially dangerous because the system may run out of pedal before the vehicle can be safely stopped.

PEDAL SINKS TO FLOOR A dangerous condition caused by a worn master cylinder or a leak in the hydraulic system will not allow the brakes to hold pressure.

BRAKE PEDAL PULSATION Indicates a warped brake rotor that needs to be resurfaced or replaced. The faces of a rotor must be parallel (within .0005 inch on most cars) and flat (no more than .003 inches of runout as a general rule on most cars and trucks, but some cars cannot tolerate any more than .0015 inches of runout). Excessive runout can be corrected by resurfacing the rotors in place with an on-car brake lathe, or by installed special tapered shims between the rotors and hub to correct the runout. A source for these tapered shims is Brake Align. Do not forget the wheel bearings (if serviceable) -- they all need to be cleaned, inspected and repacked with grease. New grease seals will also be needed.

SCRAPING NOISE FROM BRAKES Usually indicates metal-to-metal contact and the need for a long overdue brake job. Drum and rotor resurfacing will likely be needed in addition to new linings and brake hardware.

BRAKE SQUEAL Can be caused by vibrations between the disc pads and caliper, which can be cured by resurfacing the rotors, applying a nondirectional finish to the rotors after resurfacing, installing new pads and pad shims, or applying brake grease or noise compound to the backs of the pads.

BRAKE CHATTER Can be caused by warped rotors or rotors that have been improperly finished.

GRABBY BRAKES Oil, grease or brake fluid on the linings will cause them to grab. The cure is to identify and eliminate the source of contamination, then replace the linings. Badly scored drums or rotors can also grab. Resurfacing may be needed.

DRAGGING BRAKES May create a steering pull and/or increased fuel consumption. Caused by weak or broken retracting springs on drum brakes, a jammed or corroded caliper piston, a floating caliper with badly corroded mounting pins or bushings (uneven pad wear between the inner and outer pads is a clue here), overextended drum brake self-adjusters or a sticky or frozen emergency brake cable.

BRAKES PULL TO ONE SIDE Caused by contaminated linings, misadjusted brakes, a bad wheel cylinder or caliper, dragging brakes on one side or loose wheel bearings. Can also be caused by a mismatch of friction materials side-to-side on the front brakes or differences in rotor thickness, type or condition.

HARD BRAKE PEDAL Lack of power assist may be due to low engine vacuum, a leaky vacuum hose or a defective booster. Sometimes a faulty check valve will allow vacuum to bleed out of the booster causing a hard pedal when the brakes are applied. This condition can be diagnosed by starting the engine (to build vacuum), shutting it off, waiting four or five minutes, then trying the brakes to see if there is power assist. No assist means a new check valve is needed.

A quick way to check the vacuum booster is to pump the brake pedal several times with the engine off to bleed off any vacuum that may still be in the unit. Then hold your foot on the pedal and start the engine. If the booster is working, the amount of effort required to hold the pedal should drop and the pedal itself may depress slightly. If nothing happens and the vacuum connections to the booster unit are okay, a new booster is needed (the vacuum hose should be replaced, too).

On vehicles equipped with "Hydroboost" power brakes, a hard pedal can be caused by a loose power steering pump belt, a low fluid level, leaks in the power hoses, or leaks or faulty valves in the hydroboost unit itself (the latter call for rebuilding or replacing the booster).

posted 12-11-2009 10:36 PM                  

Nothing looks worse than a relatively clean $50,000 car with black, grimy wheels. European luxury sedans are notorious for having dirty front wheels because of the black dust that's generated by their disc brake pads. The dust sticks to the alloy wheels giving them an unsightly appearance.

Europeans use different friction materials than their domestic counterparts because they want their brakes to be quiet, as well as hard working. The trade-off is often increased dusting because of the black ingredients that are in the pads.

Domestic vehicle manufacturers also want good performance and quiet operation, but many use ceramic-based friction materials that produce less visible dust. The dust is still there, but it's harder to see because the compounds are usually a lighter color. And dust from many ceramic-based friction materials is less "clingy" and doesn't form a heavy coating on alloy wheels. Consequently, the wheels stay cleaner longer.

The purpose of this article is not to compare the relative merits of one type of friction compound to another, but to make our readers aware of the fact that there are alternatives to the OEM high-dust black pads that are used on many European vehicles, as well as some domestic cars and trucks. A growing number of aftermarket brake suppliers now have "low-dusting" formulas that improve wheel cosmetics, as well as brake performance.

Eliminating Brake Dust

There's no way to eliminate brake dust entirely because all friction linings are designed to wear. If the pads didn't wear, they'd soon chew up the rotors - and pads are a lot cheaper to replace than rotors.

Relatively soft nonasbestos organic (NAO) friction materials typically wear more than harder semi-metallic compounds. It's hard to generalize about the wear characteristics of ceramic-based compounds because there are so many. Wear varies depending on the formula the friction supplier chooses for a particular application. Different vehicles require different coefficients of friction, so formulas are often "application engineered" to deliver the best combination of stopping power, wear resistance, pedal feel and noise control. Most premium-quality ceramic-based linings will provide long life and wear less than an equivalent set of NAO pads on the same application.

So, the next time you see ugly brake dust sticking to your wheels, you should think about replacing your brake pads with low-dusting ceramic-based pads.

Brake Dust Shields

Another way to reduce brake dust buildup on wheels is to install "dust shields" between the wheel and hub. Shields deflect dust away from the wheel so it can't stick and form an ugly coating. Shields are relatively inexpensive and easy to install. But some people have raised concerns about these products blocking or restricting air flow to the brakes.

Brakes do generate a lot of heat, and the more aggressive the vehicle is driven, the more cooling the brakes need to prevent brake fade. When too much heat builds up in the pads and rotors, it reduces friction and increases the pedal pressure required to stop the vehicle. In extreme situations (as when driving down a steep mountain and riding the brakes mile after mile), the brakes may get so hot they fail altogether.

We've never heard of this happening under normal use on a vehicle that has been equipped with dust shields, but it may be a legitimate concern in a "severe-duty" situation. So if you are considering dust shields, buy ones that have vents. The vents allow some airflow, but keep most of the dust away from the wheels.

Removing Brake Dust

What's the best way to remove brake dust from dirty wheels? Hot soapy water or a cleaner that is specifically formulated for wheels, plus a soft bristle or foam brush and plenty of scrubbing will usually do a good job of removing the dust. Harsh cleaning chemicals or abrasive compounds, such as scouring powder, should never be used on alloy wheels. Nor should you ever use a brush with wire bristles or extremely hard plastic bristles. Scratching through the clear coat finish will open a direct route for corrosion to attack the aluminum.

There are aerosol wheel cleaning products that are safe for aluminum wheels, and many claim to require little or no scrubbing. Just spray it on and rinse or wipe it off. It's as easy as that.

To keep clean wheels clean, the buildup of brake dust can be reduced by applying a coating of wax or polymer-based protectant, or a spray-on wheel treatment. The coating will reduce the tendency of brake dust to stick to the wheels while enhancing the wheel's appearance.

posted 12-11-2009 10:40 PM                  

.

Ceramic brake pads are popular with many motorists today because they restore like-new brake performance, are quiet, long lasting, low dusting and provide safe sure stops. They handle heat much better than most nonasbestos organic (NAO) friction materials, and are quieter and kinder to rotors than most semi-metallic friction materials.

Ceramic brake pads first appeared in the early 90�s. Some vehicle manufacturers began using ceramic-based disc brake pads in place of conventional semi-metallic pads to address customer complaints about brake noise, dust and wear. Many of these ceramic pads were supplied by Akebono. Following the OEM lead, Raybestos Brakes, and other major aftermarket brake suppliers introduced their own ceramic-based friction materials. The aftermarket ceramic pads are designed to replace OEM ceramic disc brake pads and to upgrade brake performance on vehicles that were not originally equipped with ceramic-based pads.

HOW CERAMIC PADS DIFFER FROM ORDINARY PADS
One of the main differences between ceramic-enhanced friction materials and semi-metallic brake linings is that ceramic pads contain no steel wool or fibers. Steel provides strength and conducts heat away from rotors, but it also makes pads noisy. Steel also acts like an abrasive and causes rotor wear. Substituting ceramic materials and copper fibers for steel allows ceramic pads to handle the high brake temperatures with less heat fade, to recovery quickly, to experience less wear on both the pads and rotors, and to virtually eliminate noise. Annoying brake squeal is eliminated because the ceramic-enhanced compound dampens noise and moves vibrations to a frequency beyond our range of hearing.

Other features that help make ceramic pads extra quiet include chamfers, slots and insulator shims. These features are also found on other types of pads, but may not be used on all applications.

Chamfers are angled or beveled edges on the leading and trailing ends of the pad that reduce "tip-in" noise when the brakes are first applied. Chamfers also reduce the surface area of the brakes slightly, which increases the clamping force applied by the pads against the rotors. This further helps to dampen sound-producing vibrations.

Slots are grooves cut vertically, diagonally, or horizontally in the pads to reduce noise by changing the frequency of vibration from an audible level to a higher, inaudible frequency beyond the range of the human ear. Slots also help reduce brake fade by providing a passage for gases and dust to escape at high brake temperatures.

Insulator shims provide a dampening layer to absorb and dissipate vibrations before they can cause noise.

CERAMIC PADS REDUCE BRAKE DUST
Another features of ceramic pads is less visible brake dust on the wheels. All brake pads produce dust as they wear. But the ingredients in ceramic pads typically produce a light colored dust that is much less noticeable, and it does not stick to wheels like ordinary brake dust. Consequently, alloy wheels stay cleaner longer.

LONGER PAD LIFE
Ceramic pads also extend brake life compared to most conventional lining materials. Akebono and Raybestos both say their durability testing has shown significantly longer life with no sacrifice in noise control, rotor life or braking performance when ceramic pads are used compared to other friction materials.

CERAMIC PAD APPLICATIONS
Ceramic pads can be installed on any vehicle that is originally-equipped with OEM ceramic pads, or on vehicles that are equipped with Nonasbestos Organic (NAO) linings. Ceramic pads are NOT recommended to replace semi-metallic pads, especially on larger, heavier vehicles. On trucks and large SUVs, semi-metallic linings are typically needed to handle higher loads and braking temperatures.