Are you getting all of your stopping power??
The importance of brake flushing Brake fade is somewhat akin to brain fade. Reaction time is slower, usually snappy performance is replaced by a dull, mushy feel, and in critical situations the slow response time can be disastrous. While there are several mechanical reasons for this type of condition, one of the most overlooked causes is contaminated brake fluid. Most car owners are well aware of the importance of maintaining proper fluid levels in the vehicle, and reliably check to make sure that the brake fluid is maintained between the minimum and maximum marks on the reservoir. After all, if there's too little fluid, it's possible for air to be sucked into the lines, which can result in a spongy pedal feel and inefficient braking performance.
The importance of flushing the brake system ... taking the old fluid and replacing it with new ... is often not so well recognized. Why is flushing important? Conventional glycol-based brake fluid is hygroscopic, which means that it absorbs water. This is important, in order to keep condensation in the brake system from causing corrosion. However, eventually, the fluid will absorb all the moisture it can hold, reaching its point of saturation. Several things can happen at this point. Unabsorbed moisture can begin to collect in the system, causing corrosion in critical areas; the water can cause seals to swell and deteriorate, further contaminating the fluid; and the boiling point of the fluid drops beyond recommended levels. This means that under high-heat braking conditions, such as during hard braking or repeated brake application while descending a mountain, the fluid will start boiling sooner, which will reduce braking performance. The pedal can begin to feel spongy, and as braking efficiency drops, it takes longer to stop the vehicle.
How do you know when the system should be flushed? Most maintenance schedules that do specify it recommend changing the fluid every two years or 30,000 miles. If you live in an unusually humid climate, it's better to plan on doing it every year. However, your eyes can tell you when the time has come. Fresh brake fluid is transparent and has a slight amber-colored look. As the fluid absorbs moisture, it takes on a darker, cloudy appearance, which tells you it needs changing. This can also be verified empirically.