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December 2006 E-mail Newsletter
Check Your Brake Fluid
Q.) While changing my oil, I checked my brake fluid. It was a little low so I added some and noticed that the new fluid looked very clear compared to the old fluid. Is the fluid going bad or is that normal?
A.) Both. Brake fluid is the most overlooked component in the braking system of vehicles and it is one of the most important components in that system. Brake fluid is formulated to tolerate moisture absorption, control rubber expansion and corrosion, and act as a lubricant. It also must not boil or freeze in brake systems over a wide range of operating temperatures. The level is checked occasionally, but very seldom is brake fluid completely replaced unless the vehicle’s braking system undergoes a major overhaul.
Most technicians know that brake fluid deteriorates with age due to moisture and contamination. Most brake fluids are polyglycol-based. This glycol ether blend of fluids is hygroscopic, which means it attracts and absorbs moisture. This process takes place every time you leave the cap off the container or check the fluid in the master cylinder reservoir. Moisture is even absorbed through microscopic pores in rubber seals and hoses in the brake system.
Also, keep in mind that when you use your brakes, heat is generated at the friction contact points. As your vehicle sits, your brakes cool down. Therefore, over a period of time the heating and cooling action of your brake system will condense moisture in the closed hydraulics system. Most brake fluid will absorb that water and keep it from affecting hydraulic components and help prevent, or at least slow down, the corrosive action.
Even though brake fluid absorbs moisture, it cannot continue to absorb it indefinitely, which is why it is recommended that you flush the system and refill with fresh brake fluid every two years.
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