Brake fluid is hygroscopic, which means it attracts water. This means if brake fluid is more than two years old, brake bleeders and other components can become stuck because of rust. Removing a stuck brake bleeder can be difficult, but below are a few tools you will need and steps to follow to try to free the brake bleeder.
Soak the stuck bleeder with penetrating oil, overnight if possible. Spray the penetrating oil on the area beside the threads, and also through the middle of the bleeder. Attempt to remove the bleeder using a six sided socket of the appropriate size. Do not use a wrench of a twelve point socket. Many bleeder screws are made of brass or soft metal, and corners will strip, or the screw will break easily. Try to turn the screw both right and left. Even if the screw will tighten a little bit, it will free it from the rust, and make it possible to loosen it. If the screw breaks, or is broken already, skip to step three.
Clean the penetrating oil from around the bleeder screw. With the six point socket in place, heat up the area of the caliper or wheel cylinder with a mini torch. Apply even heat around the bleeder screw, and carefully attempt to turn it. Again turn the screw both right and left. If the screw will still not move, skip to step four.
If the screw breaks at any point in the process, or is already broken, use a small Ez-Out or similar screw extractor to remove the broken bleeder. Using a small hammer, tap the Ez-Out firmly into the centre hole of the brake bleeder. Using penetrating oil again, soak the entire area. With the small wrench, attempt to turn the screw out. If the Ez-Out comes out of the bleeder when turned, tap it back in more firmly, and attempt again. Do not break the Ez-Out. Screw extractors are made of very hard metal, and if broken it will be nearly impossible to remove the screw. If the bleeder does not come free, attempt using the mini torch again, trying to heat up only the area around the screw, and not the Ez-Out itself. If this doesn't work, proceed to the next step.
Drill into the centre of the bleeder using a reverse drill bit slightly smaller than the outside diameter of the bleeder screw. Make sure the drill is on the reverse, not the forward setting. Often the reverse drill bit will "grab" the bleeder screw, and screw it out. If not, it will often remove enough material that the old bleeder will disintegrate, and a new one can be installed.
Bleed your brake system according to your vehicle manufacturers directions. Many cars have a specific brake bleeding sequence or process. This can be obtained by contacting your local dealer.
If none of these steps work, replace the component that the bleeder screws into. Braking systems are critical to vehicle and driver safety. Any leaks or damaged components in a braking system can result in serious injury or death.