What you need to know before you get a brake job
Because your brakes play such a vital role in safety, some shops use fear to take advantage of their customers and sell unneeded brake parts and service. I’ve compiled this series on brake service to get you up to speed on how your car’s brakes work and how to know when they need to be serviced. I’ll also describe which parts wear out and need replacement and which parts can be reused. Then I’ll discuss the differences in brake materials and why talking to the shop about the brands they use is so important. I’ll also discuss brake job costs and disclose the most common brake job rips off to avoid.
NOTE: This is the first part of an extensive series on brakes. It can be a complicated topic so I’ve added breakdown on every component in the braking system. You can read the summaries or really dig in by reading the in-depth articles in the links at the bottom of this article.
How long do brakes last?
There’s no simple answer to this question because brake wear is directly related to how you drive and how you brake. For example, if you drive long distances at highway speeds and with few stops, your brakes can last up to 80,000 miles. But if you haul heavy loads, drive in stop and go traffic, live in a mountainous area or brake heavily, they can wear out in as little as 20,000 miles. However, there is a general rule of thumb: If you’re a typical driver with a combination of city and highway driving you’ll probably need front brake service around 40,000 miles.
Front brakes always wear faster than rear brakes
Your front brakes perform 80% of all braking, so they’ll wear out faster than your rear brakes (assuming the rear brakes or in good operating condition). That doesn’t mean rear brakes aren’t important. Just the opposite, they play an important role in maintaining vehicle stability during braking. Think about how brakes function on a bicycle. If you’re traveling at a high speed on a bike and encounter an obstacle and apply only the front brake, the braking force and your inertia tends to shift your weight over the front axle. As your weight shifts off the rear wheel, the bike frame and rear wheel lifts and potentially rotates around the axis of the front wheel, causing you to fly over the front of your bike. The same thing happens in a car. To prevent rear wheel lift, car makers incorporate a mechanical or electronic proportioning valve or equalizer valve that adjusts rear braking force to reduce weight shift and rear wheel lift and prolong brake life.
A proportioning valve provides more braking power to rear wheels
Mechanical proportioning valves are sometimes mounted at the rear of the vehicle. The valve is bolted to the body and a sensing rod is attached to the rear suspension. The left and right brake lines enter the proportioning valve from the master cylinder and exiting brake lines run to the left and right rear brakes. During hard braking the rear body begins to lift up and away from the rear suspension. The sensing rod detects the lift and moves the proportioning valve to reduce braking pressure to the rear wheels to prevent rear wheel lockup, which counteracts the lift. The harder you apply the brakes, the less the proportioning valves applies the rear brakes. In newer cars, the proportioning job is performed by the anti-lock braking system (ABS).
Anatomy of a brake system
When you apply the brakes, the brake pedal moves a piston in the master cylinder to force brake fluid down to the brake caliper. The brake fluid force pushes the caliper piston out, which forces the brake pads (friction material) against the brake rotor. The squeezing force against the rotor is what slows the wheel.
The master cylinder consists of a fluid reservoir, a piston that moves forward based on the driver’s application of the brake pedal, and fluid exit ports that direct high pressure brake fluid to calipers and wheel cylinder at each wheel. All modern master cylinders are designed to operate in a redundant mode if there’s a failure of a brake line. This is referred to as a “split system” design, where the left front and right rear brakes are supplied by one section of the master cylinder and the right front and left rear are supplied by another section. By splitting the system into two sections, your car can still brake evenly in the event of a brake line rupture.
The brake caliper receives high pressure brake fluid from the master cylinder. The high pressure fluid fills the bore at the back of the caliper piston and forces the piston to move outward where it pushes the brake pads against the brake rotor to stop your vehicle.
To learn more about how brake calipers work, read this post.
Brake caliper slides, also known as anti-rattle clips or abutment hardware
Brake pads move slightly with each brake application. To prevent vibration noise, car makers install stainless steel anti-rattle clips in the areas where brake pads move. Over time and with extreme heat, these clips can rust, causing the brake pad to bind. In addition, the high heat caused by braking can cause the clips to lose their tension, resulting in vibration and noise.
Brake caliper slide pins
A floating caliper moves along two steel pins with each brake application. The pins are coated with a high temperature grease and protected against water intrusion by rubber boots. Over time, the boots deteriorate and water enters the slide pins, causing them to corrode which eventually causes the caliper to seize and stop operating.
Brake pads are officially known as friction material. They’re built using many different formulas but they have one thing in common; their job is to convert rotational motion into stopping power. Conventional braking systems accomplish this by converting rotational motion into heat. The oldest friction materials were made with asbestos to resist the high heat. But asbestos is now outlawed and friction manufacturers now use one of four different types of materials
Nonasbestos organic (NAO): Don’t be misled by this title. The term “organic” doesn’t actually mean they’re better for your health. It just means they’re made from organic materials like glass, rubber, and carbon. The friction material is held together with fibers, filler material and high-temperature resins. NAO brake pads are the softest style, so they create less wear on brake rotors and make less noise during braking. However, due to their softness, they wear faster and create more brake dust that make your wheels look dirty. NAO pads used to be standard on smaller lighter cars, but they can’t handle the higher braking requirements of heavier vehicles. Car makers are phasing out NAO pads in place of ceramic style brake pads.
Low-metallic NAO: This is a variation of the NAO friction material where a small amount (10% to 30%) of metal fibers are added to assist with heat transfer away from the rotor face. The added metal produces slightly more noise, dust, and rotor wear than traditional NAO brake pads.
Semi-metallic: Semi-metallic brake pads provide the most stopping power of all the friction materials. They’re made from inorganic fillers with 30% to 65% metal fibers including chopped steel, iron powder, copper or graphite. The metal fillers are designed to radiate heat away from the rotor face and move it back towards the back plate where it can be dissipated by air movement. This heat transfer away from the rotor face is what makes semi-metallic pads so effective in providing maximum braking power. Semi-metallic brake pads are the hardest of all the materials, so they last the longest. But, the hardness combined with the high metal content results in more braking noise, faster rotor wear, and high brake dust levels. Also, semi-metallic brake pads work best when they’re hot, so they’re preferred for heavy vehicle that are used in stop and go traffic. But they don’t work as well when cold.
Ceramic: Ceramic brake pads are installed at the factory by more than 60% of all new car makers. They offer significant improvements over the older styles. Specifically, they reduce noise, dust and rotor wear. They’re made from ceramic fibers, bonding resins and small amounts of metal. Shops often recommend ceramic brake pads as an upgrade to NAO. Low-metallic NAO, and semi-metallic and as long as the brake pads are made by a reputable manufacturers, that can be a sensible recommendation as long as you consider your braking usage. For example, if you own an SUV or truck that was originally equipped with semi-metallic pads, you should NOT change to ceramic pads. They will provide less braking power than semi-metallic pads.
The brake rotor (disc) is the device used to stop wheel rotation. The brake caliper squeezes the brake pads against the surface of the rotor, causing it to slow and stop. The rotor is usually made from cast iron, although some composite rotors are made with stamped steel and cast iron. Rotors used on the front of the vehicle usually contain venting fins that pump air between the two friction surfaces to cool the rotor when it rotates.
Aside from wear, rust is a brake system’s biggest enemy
If you’re a highway driver and don’t wear your brakes pads, you’re not out of the woods on brake service. The brake pads and caliper slides must move in order for the system to apply and release the brake pads. If the steel backing plates on the brake pads corrode, that rust can prevent the pads from releasing, causing brake overheating, rapid pad and rotor wear, and even brake failure. The same applies to brake caliper slide pins and weatherproof boots.
Now that you have an overview of your car’s braking system click on each of these sub-topics to learn more about your brakes and how to get the best brake service.
©, 2016 Rick Muscoplat
Posted on by Rick Muscoplat