Q: Brakes fade and pedal go to the floor

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I checked the whole brake system for leaks the lines, calipers, and cylinders. Everything is dry no leaks. I got a remanufactured master cylinder and installed it. I bench bled the master cylinder before I hooked up the brake lines. I had good pedal even before I bled out the 4 wheels. I had good pedal with no sinking. I started the car and applied hard pressure to the pedal and it slowly sank to the floor. Double checked everything and no leaks. At this point I assumed it was a bad master cylinder. I went and installed a new one this time. But I still have the same problem. What are the odds I got 2 bad master cylinders? I don't know what else it could be. H E L P !

My car has 175000 miles.
My car has an automatic transmission.

The brake pedal should stay up hard when you have the engine off. As long as you do not see any loss of fluid after system is bled out of any air in the system. You may need to have the ABS module put into bleed mode to get all the air out. A pressure bleeder can also be used to purge out air in the master cylinder. If after bleeding the brake pedal fades all the way to the floor with no loss of fluid the the master cylinder internal leakage is present and needs replaced again. Make sure you have cleaned out the reservoir of any dirt and debris that may cause problem.

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