Brake fluid is a hydraulic fluid that absorbs moisture and can also deal with very high temperatures. It transfers power from your pedal to your brakes. It is also the lifeline of your braking system. Brake fluid deteriorates over time and requires regular replacement.

The corrosion inhibitors in brake fluid degrade over time. Degraded inhibitors in conjunction with the presence of excessive water cause corrosion in the braking system. After only a year of service, the brake fluid in the average vehicle may contain as much as two percent water. After 18 months, the level of contamination can be as high as three percent. After several years of service, it is not unusual to find brake fluid that contains as much as seven to eight percent water.

Most brake fluids used today are glycol-ether based. Glycol-ether (DOT 3, 4, and 5.1) brake fluids are hygroscopic, which means they absorb moisture from the atmosphere. Glycol based brake fluid starts to absorb moisture from the moment it is put in the hydraulic brake system or exposed to the air. The fluid attracts moisture through microscopic pores in rubber hoses, past seals, and exposure to the air. The problem is obviously worse in wet climates where humidity is high.

Excessive water content will decrease the boiling point of brake fluid and increase the risk of vapor lock. The compression of a vapor lock when applying the brake pedal can lead to total hydraulic brake system failure. Water also promotes corrosion of important metal brake components.

Generally, a brake fluid flush can take roughly one hour to complete.