Weber is president of Virginia-based Write Stuff. He is an award-winning freelance automotive and technical writer and photographer with over two decades of journalism experience. He is an ASE-certified Master Automobile Technician, and has worked on automobiles, trucks and small engines. He is a member of the Society of Automotive Engineers (SAE) and numerous other automotive trade associations. He has worked as an auto service technician, a shop manager and a regional manager for an automotive service franchise operation.
When was the last time you had a tetanus shot, asks the doctor when you arrive to have that cut stitched up. You need a booster every 10 years. Every year, 10% to 20% of people who contract tetanus will die. Auto repair is risky business. Make sure your booster is up-to-date.
Occasionally, we could use a booster when it comes to doing routine repairs like brake jobs. Let’s review brake system basics of pads and shoes, rotors and drums, and hydraulics.
Brakes simply turn the kinetic energy of a moving vehicle into heat energy as they stop the vehicle. That heat energy first is transferred to the rotors or drums and then is subsequently dissipated into the air. Fins between the rotor halves or on the outside of drums help with dissipation.
Friction materials have come a long way since the wood or leather block. (See the January/February 2015 issue of Auto Service Professional.)
Today’s brake linings run the gamut from semi-organic to semi-metallic to ceramic to various sophisticated blends.
Motorists want good feel and no noise from their brakes. Long ago, asbestos was the go-to friction material. It provided excellent stopping power, pedal feel and long life while being virtually noiseless.
Today, we have several options.
Non-metallic pads and shoes are typically a combination of synthetic materials that are easy on the rotors and drums, provide good stopping power and pedal feel. The down side is that they wear rather quickly and usually leave lots of dust behind.
Semi-metallic pads and shoes combine the synthetic materials with a measure of powdered or flaked metal. On the plus side, they are long-lasting and resist fade. On the negative side, they cause increased wear of the rotors and drums and require more force to stop the vehicle.
Ceramic brakes were a mixture of porcelain and clay with copper flakes mixed in. However, copper is being phased out due to water pollution issues. On the plus side, ceramics are quiet, offer good stopping, and fade and wear resistance. They also transfer much of their material to the rotors. The down side is that the friction material may appear to be a rotor problem if it is not transferred evenly due to rotor run-out. Before trashing the rotor, try your on-car brake lathe.
When in doubt, use the type of pads and shoes that originally came with the vehicle. That does not mean that you’re forced to use OE brand friction material, only that the same type of pad is installed (semi-met, ceramic, etc.).
When replacing disc brake pads, do not push the pistons back into the caliper bores without first opening the bleeder valves. Unless they are opened, any crud in the caliper will get pushed back into the brakes lines. By opening the bleeders, some of the crud will be expelled.
Most motorists ignore their brakes until they get some kind of warning, whether that involves inadequate braking, uneven braking or squeal or grinding noise. Inspect the brakes routinely when the customer brings the vehicle in for service. If the linings are getting thin, make a notation on the customer’s receipt to plant the seed for service soon.
Warnings may come in the form or noise, such as the metal tabs the GM has used for years to scrape the rotor when the linings get thin. Of course, vehicles that are not equipped with these sensors will make noise when metal contacts metal. At this point, new rotors are probably in order.
Some vehicles have electrical warnings that illuminate an icon on the instrument panel when an embedded sensor on the pad makes contact with the rotor completing the ground. When replacing pads, make sure that the new pads feature these sensors.
As to a visual inspection, new pads or shoes are called for when the gap between the backing hardware and the rotor or drum surface is thin and nearly gone.