Editor's Note: This article was orginally published Feb. 1, 2011. Some of the information may no longer be relevant, so please use it at your discretion.
I think we can all agree that the braking system is the most important safety device on any vehicle. If you still are not convinced, think about it this way: If you have a vehicle in your shop with a blown tail light bulb, bald tires, or even something more serious like a Supplemental Restraint System (SRS) problem, it does little harm if it is not on the road. Now, try to move that same vehicle out of your shop without brakes, and you might wind up going through your bay door, or worse, out into the street.
Look at it from your customer's perspective. For some, squealing brakes are a minor annoyance that can be dealt with until they can get the vehicle in for service. For others, that squeal is a major safety concern that they want fixed immediately and for good!
What are the most common brake complaints that concern your customers today? According to Rob Backode, product manager for Bosch Automotive Aftermarket Brakes, they have found they involve noise, unusual or premature wear, and dusting. In addition, other complaints involve pulsations and stopping performance, suggests Chuck Kennedy, Bendix technical training manager.
Let's take a more detailed look at each complaint individually.
Noise
Brake noise, or squealing, is drivers' most obvious problem. Unwanted, audible brake component movement causes it. Solutions are keeping brake components in place per factory specs and properly preparing surfaces during service.
"Today's brake systems are very sensitive to rust and corrosion and should receive a thorough cleaning in preparation for fresh lubricant, hardware and friction material," Kennedy says. "Residual rust or corrosion left in critical areas can begin to cause brake issues almost immediately."
In addition to normal inspections for binding, corrosion, lack of lubrication and worn or damaged components, calipers must be cleaned and special attention paid to lubricating areas of contact and proper servicing of components that retain the pads so they are clean and free of corrosion.
Great gains in noise reduction also have been made on the manufacturing side. Backode says these advances in friction technology have greatly reduced problems with brake noise.
The introduction of ceramic brake pads in the 1980s paved the way for this. This new friction technology originally was engineered for the popular Asian models. Both GM with its light-duty trucks and Ford with its best-selling Taurus made the switch by the end of the decade, spurred by a perceived lack of build quality when compared to the Asian manufacturers.
Pulsation
Russ Dobson of GM's Warren Tech Center notes that if a customer has a brake pulsation, you know you have variation, so rotors will have to be resurfaced or replaced. In his presentation to the Big 3 Brake Symposium, he related a strategy for dealing with pulsation.
"Measuring rotor thickness variation is very hard to do accurately in the shop, so why waste time trying to measure it?" he asks. "In the real world, the only things you can measure accurately are general rotor thickness and lateral runout."
Measuring rotor thickness variation requires extremely accurate measurement every few inches around the rotor and with limits as low as 0.001 in. In Dobson's words, "If the rotor pulsates, it has thickness variation and is bad."
Standard procedure for measuring lateral runout is to measure it while simulating actual conditions by mounting the rotor to the hub with lug nuts and properly torquing them into place (you are using a torque wrench, right?!), but what if there is corrosion between the rotor and hub? Would this not cause increased runout?
As rust and corrosion grow between the rotor and hub, they can separate the two, pushing the rotor out and creating runout, uneven wear and pedal pulsation. Proper inspection and a clean mounting surface between hub and rotor are key to eliminating pulsation.
So, let's say you have properly cleaned, inspected and measured. What do you do if all else fails and there is still a pulsation? According to Kennedy, "If all the rotor measurements are within specifications, the 'pulsations' the customers feel could be speed related. Checking tire and wheel assemblies on equipment designed to measure and locate loaded radial-force variations could help pinpoint problems not caused by the brake system."
Dust
When braking force is applied, small amounts of material gradually are worn off the brake pads. This material known as "brake dust" usually deposits itself on the braking system and the surrounding wheel.
The proper friction choice can affect dusting. Different brake pad formulations create different amounts of dust, and some formulations, particularly metallic brake pads, are much better at creating dust than others. Ceramic brake pads contain fewer metal particles, and therefore produce less corrosion of surrounding metal parts.
"The number of complaints about brake dust is far, far fewer with more service shops installing ceramic-type brake pads," Backode says.
Kennedy adds that, "addressing worn or corroded parts and proper cleaning and lubrication when performing a service are the best ammunition to eliminate brake dust complaints."
Taking care of a brake dust issue can eliminate other problems and help eliminate customer complaints. Using a combined effort of proper service and proper components should yield the best results. This is important because dust on wheels can be more than just a visual nuisance. If the acidic brake dust is left to accumulate, it can badly damage the finish of most wheels, so it pays to address it from the start.
Wear
Increased power and performance of vehicles in response to customer demand coupled with pressure to reduce weight for emissions and fuel economy has placed even more emphasis on brake performance. A move by manufacturers toward larger rotors, increased service area of pads and overall more aggressive braking systems is a result of the adoption of Federal Motor Vehicle Safety Standard (FMVSS) 135. That standard "requires vehicles equipped with hydraulic and electric service brakes and parking brake systems to ensure safe braking performance under normal conditions and emergency conditions" and creates an environment for increase component wear that must be serviced properly.
Given the extreme conditions under which modern brake systems operate, "premature or irregular wear both result from a failure to fully and properly restore the brake system to its proper operating condition," says Backode.
Proper restoration usually takes more than a quick pad change. Replacing all appropriate hardware, refinishing or replacing rotors as per manufacturer specs and cleaning and lubricating sliding surfaces and pins as appropriate will allow the system to function properly under the most severe loads. But driving patterns also play a part.
"Brakes on one vehicle may last substantially longer if the owner drives it easy or takes more highway trips, but if the same owner overloads the vehicle, makes short, stop-and-go trips, or leaves his foot on the brake pedal, the pads inherently will have more wear and failures from the abuse," Kennedy says.
This is where customer education is key.
Performance
Proper break-in period and technique can greatly affect the performance of new braking components. Yet not all OE manufacturers require break-in. As always, it is best to follow the individual component manufacturer's recommendation.
"A proper burnishing or break-in of the friction material and rotor surface will enhance brake performance, reduce noise and give the best life possible for the pad materials installed by mating the two surfaces together to allow proper heat dissipation and transfer of film from friction material to the rotor surface," Kennedy advises.
Another cause of performance issues is old or inadequate brake fluid. The importance of always using a high quality fluid with a high dry boiling point rating cannot be underestimated. As the brake system operates, heat is generated and transferred into the hydraulic system as it passes through various components. In addition, moisture from the environment enters the system, contaminates the fluid and decreases the boiling point. By flushing fluid at the manufacturer-recommended interval, moisture contamination is removed and the proper boiling temperature is restored.
Current issues
Improvements in engineering and manufacturing techniques as well as materials have eliminated some problems technicians see. Even manufacturer-specific complaints seem to have gone by the wayside.
"Common brake system complaints do not tend to be manufacturer-specific, but rather are usually the result of incomplete service procedures," according to Backode.
There is a delicate compromise between the engineering and design of modern vehicle braking systems. They must make sure a brake system is durable enough to reliably stop the vehicle, light enough to contribute to the overall fuel economy requirements and performs well enough to satisfy customer expectations.
Contradictions in this balance are most evident when you realize that, according to brake manufacturer Akebono, "squealing is sometimes the result of an abrasive friction material on a rotor surface" and "less robust brake systems (lighter) are much more sensitive to excitations (friction forces) that generate noise and vibration."
In the end, Kennedy suggests that "modern vehicles are simply more detail-oriented when it comes to service." Techs must follow prescribed service recommendations precisely without fail. By thoroughly inspecting and servicing braking systems, we can keep the ultimate judge, our customers, motoring down the highway safely and happily.
Jim Marotta is a freelance writer with more than 17 years' experience in the automotive industry. He currently works as a technical writer for ChiltonPro.com.
