Most vehicles use what is called a diagonally split brake system. I say most because some of the older vehicles use a front to back system. What you should do is start from the right rear wheel (rear pass.) And bleed it. Then go to your left rear(driver side rear) bleed it. Then the right front and end with the left front. Keep a good check on the fluid level being sure not to allow it to run dry. I also like to hook a big clear jar with a hose attached to the bleeder screw and submerged into brake fluid to prevent air from being pulled back through the bleeder valve. Also be sure to tell your helper not to go all the way to the floor with the pedal if you are using the old manual pump method. This can damage the internals in the Master Cylinder.
The proportioning valve can go bad but it is a rare event in my experience.
Tuesday, March 3rd, 2009 AT 1:32 PM