What are the main components of brake fluid?
4 Answers
Brake fluid is composed of the following components: 1. Component one: Polyglycol ether solvent, approximately two-thirds. Polyglycol has very high viscosity, so polyglycol ether is used to dilute it. Polyglycol ether ensures that the solvent functions properly in the fluid. 2. Component two: Lubricant base fluid, approximately one-third. The base fluid generally refers to polyglycol, used as a lubricant, accounting for about one-third of the brake fluid. These base fluids are obtained through complex chemical reactions of alkylene oxides (ethylene and propylene) with glycol or water. 3. Component three: A small amount of additives. Brake fluid requires the addition of a few additives, such as corrosion inhibitors and antioxidants, which effectively protect the brake system from corrosion, slow down the oxidative decomposition of substances, and limit the formation of acidic decomposition products and resins. Although these additives are added in small quantities, they are crucial and can significantly extend the lifespan.
In the main components of brake fluid, the most commonly used are glycol ether compounds, which are prevalent in DOT 3 and DOT 4 types. I know it typically contains glycol, additives such as antioxidants and corrosion inhibitors, which function to prevent system rust and maintain smooth hydraulic system operation. The boiling point is crucial, as the formulation is designed with a high boiling point to avoid vapor lock during aggressive braking, which can lead to brake failure—a highly dangerous situation. Brake fluid is also hygroscopic, and over time, absorbed moisture lowers the boiling point, necessitating regular replacement—generally every two years or around 40,000 kilometers. I’ve seen different vehicle models use different fluid types; DOT 5 is silicone-based, non-hygroscopic but more expensive and less compatible, so it’s essential to consult the vehicle manual when selecting fluid.
Speaking of brake fluid composition, I've been driving for years and still remember my surprise when I changed it for the first time - it's not as thick as engine oil, mainly being a glycol ether mixture with additives like rust inhibitors. The boiling point directly impacts safety - impure fluid forms bubbles when heated, causing brake failure. I once repaired an old car with unmaintained fluid, resulting in terrifyingly soft brakes. Now I use DOT 4 fluid which has more stable composition and over 230°C boiling point. Moisture absorption is another concern - fluid degrades by absorbing atmospheric water, requiring replacement every few years. I recommend checking fluid quality biannually using simple test strips. DIY fluid replacement isn't difficult, but never mix different types - combining DOT 5 with DOT 3 causes serious problems.
As an experienced auto repair professional, the main component of brake fluid is glycol ethers, which make up the bulk, along with some additives to prevent corrosion. The boiling point is crucial; if the fluid is old, the boiling point drops, leading to brake failure during high-speed braking. It's highly hygroscopic, and after a few years, the boiling point significantly decreases, necessitating a change to avoid hydraulic system issues. Don't mix different types of brake fluids; DOT 3 and DOT 5 have different compositions—one is compatible with water while the other repels it. Mixing them can damage the vehicle. It's recommended to change the brake fluid every two years as part of regular maintenance.
