Undercar: CV Joint Replacement Tips
Adapted from Larry Carley’s article in Brake & Front End.
Being able to match the right set of brake pads to the customer is critical for modern vehicles. So when a vehicle comes in for a brake job, how will you decide what kind of replacement brake linings to install? There are different brands of linings, different grades of friction materials, and different levels of quality. So, how do you pick the one that’s best for your customer?
Well, the best ones are the ones that satisfy your customer’s needs – and don’t come back to bite you. Brake work can be very profitable for a shop or dealership, but not if you have to do the same job over again for free because the customer wasn’t happy with the linings you installed. So, to reduce the risk of comebacks, you need to figure out what it is your customer really needs and which linings best match those expectations.
Every brake job is unique. Someone who drives a big Chevy Suburban and tows a boat or a horse trailer on the weekends is a different kind of brake customer than someone who commutes back and forth to work on the open highway in a Kia Rio. Soccer moms, teenagers, commuters, traveling salesmen and retirees all have different driving patterns and styles. Some rack up a lot of miles in a relatively short period of time, while others drive much less. Some are aggressive and are always on the brakes, while others take it easy and use their brake judiciously.
How a vehicle is used and how it is driven has an enormous impact on brake life. The brakes on vehicles that are driven in heavy stop-and-go commuter traffic get hot and usually experience more wear than those on vehicles which are only used for errands or highway driving. Hilly terrain and winding mountain roads will also make the brakes work harder and run hotter, too.
Brake suppliers use different grades of friction materials in their economy, standard and premium product lines, and the prices vary accordingly.
Economy linings are for bargain-shoppers who want a quick fix and little else. Economy linings should never be installed on a vehicle that has a history of eating pads or is obviously a hard-use application. Economy linings will not provide the same durability as standard- and premium-grade linings, and may not feel, sound or stop the same as the OEM linings. Economy product lines typically use only a few friction formulas, or even a “one-size-fits-all” formula. But in the real world, one-size-fits-all fits some better than others. There are always compromises because of differences in vehicle platforms, braking systems, weight and usage.
Standard linings, by comparison, are for normal-duty users, and provide good value for the money. They may or may not use the same basic type of friction material as the OEM linings, but they generally provide satisfactory performance.
The next step up are premium linings. Premium linings typically use a greater variety of friction formulas for different vehicle applications. This is called “application-engineered” or “application-specific” lining selection. The product engineers who develop and choose the friction materials try to closely match the braking performance, feel and noise qualities of the original equipment linings and the vehicle platforms they come on. Their goal is to “equal or exceed” OEM braking performance. Premium linings cost more because of this, but are also more profitable to install, and experience fewer comebacks because of noise, pedal feel and performance complaints.
Premium-grade replacement linings generally provide better wear than standard-grade linings, and certainly much better wear than economy-grade linings. Premium linings also tend to perform better in terms of stopping distance, fade resistance, pedal feel and noise control. As a rule, premium linings will restore the “like-new” feeling and performance that makes most customers happy.
One very important point to keep in mind about aftermarket friction materials (even application-specific friction) is that they are similar to the friction materials used by the OEMs, but not necessarily the same.
There are literally hundreds of different friction formulas in use on vehicles today ranging from high content ceramics to low-metallics to semi-metallics to non-asbestos organics. The exact recipes are all proprietary secrets shrouded with mystique and obscured with marketing mumbojumbo. There’s no way to know what exactly is in a set of brake linings beyond what the OEM or aftermarket brake supplier tells you on their packaging, product literature or advertising.
The term “ceramic” is a perfect example of a word that can mean almost anything. It’s like ordering pizza. Do you want mushrooms, pepperoni, sausage, extra cheese, thin crust, thick crust, hand-tossed, stuffed or what? Likewise, ceramic friction materials are not the same. There are different types and shapes of ceramic fibers. Which fibers are used and how they are combined with other ingredients determines the noise, wear and braking characteristics of the friction material.
One brake supplier told us that they use more than 20 different ceramic formulas in their ceramic product line alone. Others use only a single ceramic formula. Those who sell single-formula ceramic linings typically suffer from high “Mu Variability” – that’s engineering lingo for a lot of variation in hot and cold friction coefficients. This results in fluctuating stopping power as the brakes heat up. It can also lead to comebacks if your brake customer is unhappy with the way their brakes feel.
According to industry sources, ceramic linings are now used on 75% of 2004 cars and light trucks. But some linings are low-content ceramics, while others are high content ceramics. Some formulas contain up to 30% iron to help dampen noise, while others use little or no iron.
Confused? We’ll you should be. The bottom line here is that you really have no way of knowing what exactly is in the OEM linings, what is in the aftermarket replacement linings, or how closely the linings you choose to install will actually match the braking performance, feel and quietness of the OEM linings. All you can do is follow the friction supplier’s recommendations and hope they’ve done their homework in choosing a material that works well on the application and keeps your customer happy (and safe).
Making it Safe
Brake suppliers use a variety of methods to make sure their products are safe and provide good braking performance. This includes various kinds of laboratory testing, as well as on-vehicle and fleet testing. Years ago, the Brake Manufacturer’s Council (BMC) developed a brake performance test called J1652 for comparing friction materials. This later led to a more advanced test called J2430 which uses a special dyno to simulate brake performance on a vehicle.
The purpose of mentioning these various test procedures is to make you aware of the fact that all of the major name brand brake suppliers are very rigorous in their testing and go to great lengths to make sure their produces are both safe and well-suited to the vehicles they are installed on. That’s not necessarily true of some offshore “no name” brake suppliers. Their test methodology may not be as sophisticated nor as extensive as their better known counterparts. But when you’re competing on price in a very competitive market, you can’t have everything.
To reduce some of the confusion that goes with selecting replacement linings, one brake supplier told us they recently revamped their catalog. They now list all their different linings that fit a particular vehicle application, but boldface the one that their engineers recommend as the best all-round choice. That should make it easier for parts suppliers and installers who may not be familiar with all the company’s product lines to choose the best lining for the application.
Handling the Heat
Most brake suppliers also have a “severe-duty” or “heavy-duty” brake line that’s a step up from their premium product line. Typical applications include fleet vehicles, taxis, police cars, limos, ambulances, vehicles used for heavy towing and hauling, and street performance cars. These are all applications where the brakes run hot and work hard. The linings that work best in these kinds of applications are usually high temperature semi-metallics with a high percentage of steel or iron content.
Sustained high brake temperatures of 400 to 500 F (which can occur when the driver constantly rides the brakes in heavy traffic) are actually harder on brake linings than peak temperatures that may shoot up to 600 to 800 F momentarily, but only remain there for a brief period of time. As we said earlier, brake wear is directly proportional to brake temperature, so the hotter the brakes get (and the longer they remain at elevated temperatures while braking), the faster the linings wear.
Semi-metallic friction materials with a high iron or steel content can handle heat much better than ceramics, low-metallics and non-asbestos organic materials. Semi-metallics will wear less and fade less as brake temperatures rise. But the trade-off to switching to a semi-metallic may be increased noise and rotor harshness. And strangely enough, wear may even be greater with a semi-metallic if the brakes never get hot enough to break-in the pads or to push the pads into their intended temperature range.
Another upgrade possibility here is to also install slotted and drilled rotors. These are a popular appearance add-on with owners of sports compact cars and street performance cars and light trucks, but they can also improve cooling to reduce heat fade and wear. If the rotors have to be replaced anyway because of wear, upgrading to slotted and drilled rotors may help the brakes last longer.
The best indicator of a “heavy-braker” is worn linings at low mileage. If a car or truck with less than 30,000 or 40,000 miles on the odometer (or since the last pad replacement) needs new linings, talk to your customer about their driving habits and how they use their vehicles. Many people who are hard on brakes don’t think they’re doing anything unusual. They see themselves as “normal” drivers who are driving the same as everybody else. Vehicle manufacturers typically place a much higher priority on quiet brakes than brakes that last. They don’t want any problems during the warranty period, which is typically three years or 36,000 miles. After all, brake linings are a wear item and are expected to wear out. So the OEMs may use softer linings that are quiet, but don’t necessarily provide much durability beyond the warranty period (which is another reason why aftermarket brake suppliers don’t match OEM formulas exactly – especially if wear is a problem with the OEM linings).
Seeking the Answers
You can often identify vehicles that eat brakes by their appearance and/or the accessories on them.
Does a vehicle have a trailer hitch? Does the hitch appear to be well-used? Ask the customer what he hauls and how often.
If the vehicle is a pickup truck, does the bed show a lot of wear or abuse that would suggest it is being used to haul a lot of stuff?
Does the vehicle have sporty aftermarket wheels, low profile street performance tires, a big wing on the back and a muffler with a coffee can-sized outlet? The things definitely point to a lead-footed driver who will need a brake upgrade.
If the vehicle is a SUV or minivan, is it full of “kid stuff” (car seats, sporting equipment, strollers, toys, candy wrappers, etc.) that would suggest a lot of short trip errand driving? Premium linings should be recommended here.
Is there a pizza delivery magnetic sign or flag on the vehicle? Or a stack of empty pizza boxes in the back seat? The vehicle probably needs premium linings.
If pad wear is not an issue and your customer is more concerned about noise, feel and all-round braking performance, premium-grade application-specific linings also should be your first choice.
Switching to a low-dusting ceramic lining may also satisfy the customer who drives an expensive luxury vehicle and doesn’t like ugly black brake dust on his alloy wheels.
To sum up, you have a lot of brands and different types of friction materials from which to choose. So don’t just use the same old linings on every job you do. Think about the application, how the vehicle is driven, who your customer is and what type of linings might best satisfy their needs. Then make your recommendation and, if necessary, explain your logic to make the sale. Hopefully, your future brake customers will agree and everybody will be happy.