Bleeding and checking for leaks is not the answer. Leaks or air in the lines will prevent brake fluid pressure buildup. You have the opposite problem where the pressure is being trapped and can't release. There's three common things that can cause this when all four brakes are involved. Probably the most common is when the brake light switch is misadjusted and is holding the brake pedal down a little. That usually happens when the plastic or rubber cap on it falls off, the brake lights stay on, and someone tries to readjust the switch but sets it too far to let the pedal come all the way back.
The second is when the master cylinder or power booster are replaced, and the booster has an adjustable push rod. Most of the time that adjustment is correct, but it's adjustable because production tolerances on the assembly line weren't very tight. Sometimes people readjust the push rod in a misguided attempt at solving a low brake pedal problem.
Either of those first two conditions will prevent the pistons in the master cylinder from returning fully and opening the fluid return ports. The clue is if you loosen the master cylinder mounting nuts and pull it forward 1/8", the bakes will release.
The third cause is brake fluid contaminated with a petroleum product and is really serious. That will cause rubber parts to swell. The clue is the rubber bladder seal under the reservoir cap will be blown up and mushy. Also, loosening the master cylinder's mounting nuts will not let the brakes release. The lip seals on the pistons will be mushy like that too, and they'll grow past the fluid return ports, blocking them. Two brakes will again release if you open one bleeder screw, but they'll also release if you loosen a steel line right at the master cylinder. If the reservoir is of the right design, and you remove the cap, you'll be able to see the fluid spurt up a few inches when you quickly push the brake pedal. That won't happen when the seals have grown due to fluid contamination.
That contamination can be just a trace of engine oil, transmission fluid, power steering fluid, or axle grease. Experienced mechanics even wash their hands with soap and water before handling rubber parts that touch brake fluid to prevent getting fingerprint grease on them.
A 16-year-old car will usually not be worth repair if the brake fluid is contaminated, especially if it has anti-lock brakes. The only proper repair is to remove every part that has a rubber part inside, flush and dry the steel lines, then install new rubber-containing parts. That includes calipers, wheel cylinders, master cylinder, four flex hoses, combination valve, and the ABS hydraulic controller and rear height-sensing proportioning valve on vehicles that have them. If any part is not replaced, the contamination will leach out of the rubber part and recontaminate all the new parts. This means your new master cylinder would be contaminated.
Sunday, October 19th, 2014 AT 7:07 PM