Many mechanics recommend that you change the brake fluid in your car every couple of years, to ensure your brake system continues to work effectively and to prevent damage to the components. It is not difficult to change brake fluid, but you will need several new containers of brake fluid, a short length of clear tube, a wrench that fits the brake bleeder valves on your caliper, and either an assistant or a one-man bleeder kit. Be sure to use either DOT 3 or DOT 4 brake fluid, as DOT 5 and 5.1 are intended only for race cars and cannot be mixed with the types used in regular vehicles.
Before you change brake fluid, many mechanics suggest cleaning the outside of the master cylinder to prevent dirt from entering and contaminating the system. Then you will need to open the reservoirs and draw out the old brake fluid with a siphon. An old turkey baster will also suffice.
Once the old brake fluid is removed, fill each brake fluid reservoir with new fluid from a container you have just opened. Then you will need to pick a wheel to start with. With the wrench, loosen the brake bleeder valve so that it will be easy to turn when the time comes. If it is stuck shut, spraying the valve with penetrating oil or heating it with a lighter may help loosen it. Just be careful not to break off the valve, as you will then have no way to bleed the brakes without either drilling out and replacing the broken valve, or replacing the entire caliper!
At this point you will need to have your assistant sit inside the car so they can step on the brakes for you. With the clear tube over the bleeder nipple and a drain pan underneath, open the valve, and then ask your assistant to step on the brakes. Old, dirty brake fluid will stream through the tube and into the drain pan. Once the pedal is down, your assistant will need to tell you so that you can shut the valve. Only then should they take their foot off the brakes; taking it off too soon will draw air back up into the system.
Repeat these steps until nothing but clean, clear fluid comes out when the brake pedal is depressed. Have your assistant keep an eye on the brake fluid reservoir, and refill it as needed. If you accidentally suck air into the system, you will need to repeat the above steps several times, until no air bubbles show up in the fluid as it streams through the tube. When you finish each wheel, move on to the next and repeat the entire process, until all four wheels have been bled. Then just close the brake fluid reservoir, double check the bleeder valves to make sure they are closed, and you are all done!
It is important to change brake fluid about every two years in order to maintain a clean, working brake system. Brake fluid is designed to absorb any moisture in the brake system. This keeps your brake system in good working order, but it also shortens the life of the brake fluid. When the fluid has absorbed too much moisture, it will boil at a lower temperature, and when that happens your brakes will stop working. In addition, moisture tends to have dirt in it, which gets into the brake components and can eventually damage them.
Also, because brake fluid absorbs moisture, old, opened containers of brake fluid cannot be reused. Always buy brand new containers any time you change brake fluid.