Brake system tech: Plus safety issues for the customer — and your shop
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.
Should you encourage your customers to change their brake fluid? They may balk. After all, seldom is there any mention of this as a periodic maintenance service in many owner’s manuals.
European auto manufacturers are more adamant about replacing brake fluid than their American counterparts. Besides, European service is almost exclusively done at dealerships rather than at independent shops like we have in the U.S. European car owners also tend to be more fastidious about maintaining their vehicles. But brake fluid flush and fill intervals are now creeping into domestic maintenance schedules.
Brake fluid flushing was seldom done in the past. How many times have you performed the service on your own vehicles? Of course, we could ask how many times you have purged your water heater. For the most part, neither task has really been an issue. Nevertheless, we would bet that you have replaced a water heater at least once due to neglect.
The same could be said for brake system hydraulic parts. Without occasional service, components could fail. Some, like wheel cylinders, are cheap. Some, like ABS components, aren’t. Any contaminants that get into the ABS modulator assembly can cause expensive damage. Spending about $100 on a brake fluid flush and fill can save thousands on ABS repairs or at least hundreds on caliper or wheel cylinder replacements.
Water in the brake fluid leads to corrosion, but where does the water come from? After all, the hydraulic system is sealed — it is a closed circuit. The only time it is even open to the atmosphere is when the cap on the master cylinder reservoir is removed to add fluid. And you really should not have to add fluid unless there is a leak.
Since brake fluid is hygroscopic, water can also be drawn through the microscopic pores of rubber hoses and even the reservoir vent. Although there are corrosion inhibitors in the fluid, they wear out over time — up to 90% in as little as three years. The more depleted they are, the less moisture it takes to cause corrosion damage.
How often should your customers change their brake fluid? Some carmakers, particularly European manufacturers, specify fluid changes in their vehicles’ owner’s manual—usually annual inspections with flushes every two years. Fluid change frequency also depends on geographic location. Humid conditions are worse than arid ones. For the typical car owner, you may suggest changing it every two to three years.
But for safety’s sake, offer to check the fluid at least annually. Experts claim that systems absorb as much as 3% water by volume in just 18 months.
Fresh DOT 3 fluid is required to have a boiling point of at least 401 degrees Fahrenheit. That level of 3% water can lower the fluid’s boiling point to 293 degrees F. So it’s easy to see that fluid older than 24 months can represent trouble waiting to happen.
Using paper test strips to test for water content, which was tried at one time, does little to indicate the fluid’s condition. A refractometer provides an accurate measure and an electronic refractometer, although not cheap, makes testing easy. Another trick is to use your DMM. Connect its negative lead to the negative battery post and probe the fluid in the master cylinder reservoir. Any reading over 0.30 volts indicates excessive water present.
As the amine corrosion inhibiters in brake fluid break down, copper migrates out of the brake lines. It is a rare sight, but green stuff in the reservoir is a sign of copper. Copper is like the canary in a coal mine — an early warning of trouble. Testing for free copper ions is easy with test strips designed for brake systems. The various shade of purple represent the concentrations of copper. They also provide a good show-and-tell demo when marketing a fluid flush to your customers.
The corrosion protection can decrease even without the presence of water, especially if the vehicle is driven hard, is used to pull a trailer or is driven in mountainous terrain.
When the corrosion protection gets low the fluid should be changed and fresh fluid meeting US Department of Transportation (DOT) standards must be used. Most vehicle manufacturers call for DOT 3 brake fluid which has a minimum dry (no moisture) boiling point of 401 degrees F. DOT 4 fluids have a boiling point of 446 degrees. But always use the type of fluid specified for the vehicle.
Some European vehicles use mineral oil fluids. The advantage is that mineral oils do not attract water. But do not attempt to use them in vehicles designed for glycol-based fluids or the rubber parts of the brake system will be damaged. Mineral oil brake fluid is dyed green.
Silicone fluids were tried for a while, but any moisture that gets into the system is not absorbed by the fluid as it is in glycol-based brake fluids. Hence, the water tends to form vapor bubbles as it heats up to a relatively low 212 degrees F, or the water can freeze and cause an ice plug.
The distinct advantage of silicone fluid is that it will not damage paint like glycol fluids (this is why many collector-car owners may prefer silicone fluid, and was one reason Harley-Davidson used it, but even Harley has switched to glycol). Also, silicone brake fluid should never be used in a system that features ABS, since quick pressure modulation can cause the fluid to aerate/foam, resulting in temporary reduction of brake system pressure.
Why is the fluid’s boiling point important?
As you know, energy can neither be created nor destroyed. It can only be transferred. When you apply the car’s brakes, the kinetic energy of the car in motion is changed into heat energy by the pads and shoes against the rotors and drums. The heat then dissipates into the surrounding air. But under hard or prolonged braking, excess heat is also absorbed into the fluid. When that happens, any water in the fluid may boil causing the brakes to fade or even fail.
It is not uncommon to find metal-to-metal contact between the brake pads and rotors, particularly in states without a periodic motor vehicle inspection program. Most motorists have no idea what that noise is and ignore it in hopes that it will go away. As you know, it never does.
Another source of rotor damage is uneven lug nut torque. It happens too often and too easily. Even when the owner changes a tire, he can tighten the fasteners unevenly or excessively. Some shops don’t even use a torque wrench or torque sticks when working on wheels, which is difficult to believe in this enlightened age. Yes, we have heard the argument that torque sticks do not have the calibration of a torque wrench, but more important is being off a few foot-pounds unevenly and warping the rotor.
In their never ending quest to reduce weight (and improve fuel efficiency), carmakers have whittled away at weight and that includes brake rotors. The former beefy rotor has been replaced with something looking more like a slice of deli ham. Most carmakers now discourage refinishing the rotors with each and every brake job. If you find no damage, leave them alone. But if the rotors are dished, suffer thickness variations or have lateral runout, you must restore them to perfection (or replace them).
A dished (tapered) rotor usually causes a spongy pedal, especially following lining replacement. The old linings may have actually conformed to the dished condition. Using a micrometer, measure the rotor thickness at several points from the center out to the edge and at several spots around the clock.
Thickness variation is commonly caused by hot spots in the rotor, resulting in pedal pulsations. Instead of the contact faces being flat, they resemble a lumpy bagel. Again, use a micrometer to check that the rotor has even thickness along the entire path of pad contact.
Lateral runout is the number one cause of brake pedal pulsation. And pulsation is the number one complaint from the car owner. Noise is number two and we will get to that later. Use a dial indicator to inspect for lateral runout.
An on-car lathe can salvage many out-of-spec rotors, but far too often so much metal gets removed that the rotor reaches the discard limit. Then, about the only option is to install replacement rotors. Yes, we said rotors as in plural. Don’t risk a comeback by replacing just one. After all, the price of most replacement rotors will not send your customers in search of a second mortgage. If, however, the rotor still has enough meat, but runout is excessive, another option is to install a shim between the rotor and hub. This may be an option for a new rotor that is otherwise in good shape.
As stated earlier, noise is the second biggest complaint from car owners. Noise or brake squeal may emanate from vibrations between the pads and rotors, the pads and calipers or the calipers and the mounts. Worn brake hardware is often the cause of vibrations, so replace the bolts, slides, bushings clips, shims, insulators and/or springs with each brake job. Remember to lube all moving parts with the proper high-temperature grease. And you may want to use a bit of chemical anti-noise compound on the back of the pads for good measure.
Improperly machined rotors are another source of problems. Be sure to give them a non-directional final finish after turning them with a lathe. Make sure to clean any grease from the brakes before installing the wheels (following a wash with solvent, it’s a good idea to also wash and scrub the rotor with hot soapy water. This helps to remove any residual contaminants).
Everybody has had at least one customer return complaining that their vehicle does not seem to brake as well as before. They are often right, especially if the rotors have been machined or replaced. Over time, some of the brake material has been transferred from the linings to the rotors. This is a good thing and improves brake feel. After a brake job, however, it may take quite some time for this transfer to happen. Meanwhile, the customer is unhappy. Unhappy, that is, unless you have finished your job and put the icing on the cake. Your job is not done until you burnish the brakes. How?
Make about 20 stops, or near stops, from around 35 mph to 40 mph, allowing a minute or two between stops to allow the brakes to cool. Do not use heavy pressure, but brake as you normally would. Proper burnishing also reduces potential noise issues. Granted, most of us don’t have that kind of time, but even 10 deceleration cycles will cut down on complaints, so finish the job properly.
On relatively new vehicles, you may simply squeeze the caliper piston(s) back into the bore before replacing the pads. If you chose to do that, open the bleeders so that any crud floating around in the calipers is expelled instead of pushed back into the brake hoses. But if the vehicle has been in service for a few years or this is not the first brake job, you may have to rebuild the calipers. It is not a difficult job, but it does take a little extra time at the workbench that may well be worth it to avoid a comeback. Of course, if you discover corroded pistons or damaged bores or seal channels, don’t mess around. Simply replace with new or quality reman calipers.
Only Superman can inspect the condition of the seals and pistons inside the rotors. That is why many techs now prefer to install loaded calipers — calipers with pads — that usually come complete with new hardware. It doesn’t take much longer to swap out the calipers than to swap out the pads. Besides, this provides an opportunity to flush and fill the hydraulic system with fresh brake fluid.
Brake friction material has come a long way since asbestos was banned by the Environmental Protection Agency (EPA) in the late 1980s. Yet, due to legal challenges, some asbestos has been legal in automotive friction material.
If you aren’t sure what kind of lining the vehicle you’re working on has, use all the precautions that you normally would for asbestos dust. Never ever blow the dust from a brake assembly using compressed air.
Not only is asbestos being banned, some metallic elements blended into friction compounds are being banned. In a general overview of the regulations, Peter Murnen, global marketing director, undercar and visibility products, Federal-Mogul Corp., stated: “In Washington state, brake manufacturers are required by 2013 to provide detailed information concerning the levels of materials like copper, nickel and zinc in each of their friction formulations. The state will use this information to establish baseline levels for future friction materials.
“Manufacturers selling brake products in both Washington state and California will also work with an outside testing agency, NSF International, beginning Jan. 1, 2013.
“The next major milestone... will be Jan. 1, 2014, when friction materials may not exceed established levels of certain compounds, such as lead, asbestos fibers... as well as chromium six and cadmium. Then, beginning in 2021 manufacturers cannot sell friction materials that have greater than 5% of copper by weight. In 2024, the copper content must drop to less than 0.5% by weight. The elimination of copper is significant because most ceramic friction formulations use copper as an abrasive element.”
Regulations on copper content are intended to reduce the amount of the material that’s entering waterways and water tables.
Wagner, a Federal-Mogul brand, reportedly has already begun to transition some of the latest low-copper formulations into its aftermarket line of ThermoQuiet CeramicNXT pads.
Also on the technical front, ACDelco has introduced a surface coating to its brake pads that helps reduce the break-in period and improves pre-burnish brake effectiveness for police cars, according to the company. The coating is designed for the police duty cycle, including high-speed driving. The new coated pads provide coverage for Chevrolet Caprice, Impala and Tahoe; Ford Crown Victoria and Interceptor; and Dodge Charger police vehicles.
During pad break-in or “burnishing,” the ACDelco coating that was applied to the friction surface during manufacturing transfers quickly to the rotors. The coating may temporarily release visible airborne gasses as it transfers material onto the brake rotor during the burnish procedure, according to the company.
The new pads would be available only to professional installers who service fleet vehicles. ●