How to Bleed Brakes
Ok, let's get into how to bleed brakes...
Brake Bleeding can be tricky... Sometimes they bleed right away, and sometimes you can fight it for hours. It kind of depends on your brake system.
Always start with the wheel the furthest away from the master cylinder and end with the one closest.
Always use new, unopened brake fluid. Brake fluid is hygroscopic. That means it absorbs water. Water in the system will corrode the inside of your system. Older opened containers will have absorbed water and should be disposed of.
Brake systems with the master cylinder below the calipers or wheel cylinders (under the floor) can be tough. This is when you need the residual valves in the system. See "Designing Your Brake System". They act as a one way valve. 2 lb valve for disc and 10 lb valve for drum.
There are as many opinions on how to bleed brakes as there are opinions on what engine is the best. We will cover some of the most successful...
-One way to bleed your brakes is with a clear plastic bottle, a clear piece of 1/4 inch inside diameter tubing, and some new brake fluid. Make sure the bottle is stable enough so it won't fall over.
Fill the bottle with about 1 inch of new brake fluid so that the end of the hose is in the fluid. Install the other end of the hose over the bleeder. Crack open the bleeder screw on that wheel cylinder, and slowly press the brake pedal several times until air bubbles stop coming out of the wheel cylinder or caliper.
Now close the bleeder, top off the master cylinder with brake fluid, and move to the next farthest wheel. Repeat the process at each wheel.
-A method similiar to above uses an aftermarket bleeder screw called a speed bleeder. It only lets fluid out, then a spring loaded valve shuts so that air can't return into the system. While I haven't tried the speed bleeders, people that have tried them swear by them.
-Another way is to pump up the brake pedal a few times, open the bleeder to allow the fluid to run out until the brake pedal goes to the ground, close the bleeder and repeat. This however takes two people. The previous two methods can be done by one person.
Many experts believe this method can aerate the fluid from the pumping causing air to stay in the system. However, if the pumping is done slowly and smoothly, this process does work. If you do get milky looking fluid from aerated fluid, let it set for a day and try again.
Dot 4 and above tend to aerate more, so it can be tougher to bleed with it. Dot 3 is really the best for bleeding and has always worked great! There's no real need to spend more for anything else.
Use only the type of fluid specified by the vehicle manufacturer. Do not mix different types! Using DOT 3 in an application that calls for DOT 4 might create a safety hazard. The newer stuff is made for newer systems and is usually only used if it specifically calls for it.
-They also sell units that will attach to the master cylinder and push the fluid through the system.
-There are also units that attach to the bleeder and force fluid backwards through the system to the master cylinder to push air out.
-Another type that's been around for a while is the unit that draws fluid through the system with vacuum.
The aftermarket units above will also do other automotive jobs, so it may be worth it to get one.
-One final word: Be neat! Spilled brake fluid will remove paint!
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