Most vehicle owners understand that dirty engine oil, transmission fluid or antifreeze can be harmful to their vehicles. What about brake fluid? Some may understand that the master cylinder reservoir should be topped off if the brake fluid level drops, but what about flushing the fluid on a regular basis? According to the Car Care Council, the brake fluid in a typical vehicle can become contaminated in two years or less. Most domestic OEMs do not have a time- or mileage-based brake fluid replacement requirement, specifying only that the fluid be inspected at regular intervals. Many import manufacturers do recommend fluid replacement at prescribed intervals.Brake fluid is hygroscopic, which means it readily absorbs water. Water is absorbed through the rubber parts in the system, including the brake hoses and seals, and every time the reservoir cap is removed. Water contamination will appreciably lower the original boiling point of the brake fluid, and increase its viscosity at low ambient temperatures.Beyond the vaporization hazard, water contamination may also cause corrosion of brake cylinder bores and pistons, and may seriously affect the braking efficiency and safety of the brake system. Moisture creates an additional problem for owners of vehicles equipped with antilock braking (ABS) systems. Rusted and corroded ABS components are very expensive to replace.It has long been thought that the moisture absorbed in the brake fluid was the sole source for the corrosion that takes place in valions brake parts. It turns out that it’s only a contributing factor. Corrosion has also been found in some brake systems that did not have significant amounts of moisture present. How could this happen?Corrosion inhibitors, p H stabilizers and antioxidants are added to brake fluid to improve long-term brake system corrosion protection. Over time these corrosion inhibitors can become depleted, leaving the internal parts of the brake system vulnerable to corrosion. There are many variables involved in determining how long it takes to deplete the corrosion inhibitors, including brake fluid chemistry, chemical and thermal stability, brake system design, driving habits of the operator, frequency of maintenance, temperature and road surfaces.Studies conducted by the National Institute of Standards and Technology found the rate of depletion is fastest at the wheels. This is where the fluid is exposed to the highest degree of heat, which accelerates corrosion inhibitor breakdown. Vehicles with ABS show even faster degradation, due to the circulation of fluid caused by the cycling of the system. This, combined with the fact that ABS systems use close-tolerance valves and other precision parts, makes them more susceptible to the effects of corrosion or deposits.Copper has a direct role in the corrosion of the brake system, as well as providing an indirect indication of the age of the brake fluid. Copper in the brake lines corrodes at a slow rate over several months or years, resulting in copper ions in the brake fluid. These ions then act as oxidizers and plate out in the ABS valves when the corrosion inhibitors can no longer prevent corrosion of the ferrous components. The rate of corrosion of the copper is dependent on the level of corrosion inhibitors remaining in the brake fluid.This copper corrosion acts as an early warning for the next type of corrosion that appears in the system. Dissolved iron appears in the brake fluid after the initial ammine corrosion inhibitors are significantly depleted and dissolved copper levels rise to around 200 ppm. By the time yon see significant levels of iron in the brake fluid, severe corrosion is active. Once iron corrosion begins, the copper in the system acts as a catalyst to speed corrosion. Particles and sludge accumulate in the brake system, especially the ABS unit, which may interfere with operation. Based on what is now known about brake fluid degradation and contamination, the Motorist Assurance Program (MAP) has added the following recommendations to its Uniform Inspection and Communication Standards:* Suggest testing brake fluid at OE-recommended brake system inspection service intervals to ensure copper content is below 200 ppm.* Require brake fluid replacement if copper content exceeds 200 ppm.* Suggest brake fluid replacement at vehicle-specific OE replacement intervals (if they exist).The color of brake fluid alone should not be used as an indicator of its condition. Test strips produced by Phoenix Systems provide a measure of the copper in the brake fluid, which indirectly measures the level of corrosion inhibitors in the system. Fluid Rx uses a different fluid test method, called radial planar Chromatographie diagnostics. A drop of fluid is placed on a test pad. In both cases, changes in the test medium are used to determine fluid condition and service recommendations.If the fluid requires replacement, either due to an OE manufacturer’s service recommendation, a fluid tester or test strip failure, or because you’re installing other new brake components, flush the system with equipment designed for the purpose. The object is to get as much of the old fluid out of the system as possible, and replace it with clean fluid, without introducing any air. Dedicated flushing equipment attaches to all four bleeder screws simultaneously. The equipment pressurizes the master cylinder reservoir to introduce the new fluid, and the whole job can be completed in 10 to 12 minutes. In addition to assuring the continued safe operation of your customers’ brake systems, brake flushing can be a profitable addition to your shop’s range of services.
Archive for December, 2007
Hybrid Safety: Important Tips That Could Save Your Life By Craig Van Batenburg, AAM
Some of you have taken my gas and electric vehicles (hybrids) class, but most haven’t. Safety is a big part of the course. The Toyota Prius and Honda Insight and Civic gas hybrids are out there. They will have accidents and you will be asked to fix them. Collision shops are usually the first to experience the difference.So far we have not lost a technician to any electric-only vehicle (EV) repairs, but these techs are typically trained for one week on high-voltage systems. I sure hope the average tech prepares very well before he or she starts to work on a hybrid car. A large spark that would sometimes make a tech jump and a co-worker laugh may not seem so funny if the technician is hurt or, worse yet, dead. The safety issues are real. Read this carefully and pass it on to each associate in your shop.The threshold for voltage that can be fatal, as in dead, is about 60 volts. For some people, it’s as little as 50 volts. Hybrids use a dual voltage system: 12 volts for most of the car and high voltage (HV) for the drive motor(s) and related systems. The HV is what you need to respect. Electricians who have worked on 110v or 220v know to be careful and de-power the wires before working on the system. Well-trained electricians wear safety gloves, work in teams and know how to read a meter. The Toyota Prius is 276 volts, a lethal amount; and both Honda hybrids come equipped with 144 volts as standard equipment. Always wear safety gloves during the process of de-powering and powering the system back up again.
I want to see you in class some day, so don’t be foolish. If you have any doubts about your ability to perform these safety steps, then leave this for someone else.
Safety in the OvenFor collision shops, don’t bake these hybrids at temperatures over 150 degrees F. Those nickel-metal hydride (Ni-MH) batteries really don’t like extreme heat. Cook a battery pack in a Prius and you are out almost $5,000 and that is only for parts.