Posted by Dave'02LT on December 10, 04 at 05:27:23:
There is a trick to bleeding brake systems that I have never seen posted on the forums I visit. It is especially useful when replacing the master cylinder(MC) or after repairing a major leak. Here goes...
If replacing the master cylinder, first bench bleed with the fittings and lines that circulate the fluid back into the reservior. If you're lucky they came with the MC, otherwise you'll need to buy a kit.
Then mount the MC to the car. Unscrew the line kit and hook up the brake lines quickly to minimize the amount of air into the system. Top off the reservoir, then place a 2x4 under the brake pedal to prevent it from going all the way to the floor.
Here's the trick: Once you have a helper ready, crack the lines at the MC open a quarter to a half turn, then have the helper slowly push the pedal to the floor. Once the pedal is down close the brake lines. Then have the helper let off the brakes. Allow it to rest for a few seconds, then crack the lines open again and the helper pushes to the floor again. Close off, release, ect. Repeat until no more air comes out of either line. It usually only takes 3 to 6 tries to get all the air out. Don't let the reservoir go empty.
Once the MC has been bled this way, bleed the rest of the brakes in the normal fashion, ie slowly pump the brakes three times, hold pedal down, and bleed Right Rear first, then Left Rear, then Right Front, then Left Front.
There are some master cylinders where bench bleeding is not practicle or possible due to design or lack of adapters. The above method is particularly useful in that situation, though you will have to repeat many more than 3 -6 times. I've had friends call me in desperation after pumping a gallon of brake fluid with poor/no results, that have then solved the problem with the on car 'bench bleeding' method. Hope this helps.