Guide to Brake Fluid Maintenance

Brake fluid is an often overlooked part of regular vehicle maintenance. Many vehicles suffer from brake system problems as a result of negligence, repairs that could have been avoided with the proper preventive maintenance.

The Federal Department of Transportation  (DOT) grades brake fluids; most vehicles to be found on American roads use DOT 3 or DOT 4 brake fluids. These types are very chemically similar, although DOT 4 boils at a higher temperature than DOT 3.

DOT 5, a silicone-based brake fluid is not recommended for vehicles that use ABS. Its resistance to moisture absorption, may seem like an advantage, can actually cause the water that finds its way into the hydraulic system, to collect in pockets where it may boil or freeze. DOT 5 also doesn’t mix with other types of brake fluids. 

Most standard brake fluids absorb water over time and are usually fully saturated after two years, which is why most service professionals recommend a two year brake fluid replacement cycle. If the saturated brake fluid is not replaced it can cause hydraulic system parts, including expensive ABS components to suffer internal rust damage. Another reason your brake fluid should be regularly replaced is that “wet” brake fluid boils easier than when it’s fresh. 

Keep in mind that although two years is a standard maintenance time frame, for brake fluid replacement, water absorption rates can widely vary depending on vehicle design, climate and driving conditions. Other contaminants from foreign materials may also cause issues with your brake fluid performance, so the two year replacement program is more of a suggestion than a strict maintenance plan for vehicle owners to follow.

Checking on your brake fluid’s condition used to be difficult, because a refractometer or fluid sample boiler with spectrographic analyzers was needed – equipment was not often available in vehicle maintenance shops. However, today there are test strips available that can allow you to check on your brake fluid’s moisture content and contamination level.

How regularly do you replace your vehicle’s brake fluid?

Information provided by Jay Buckley of Bendix.

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