brake problems

2007 KIA RONDO
147,000 MILES • 2.7L • V6 • FWD • AUTOMATIC
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ALAIN COURNOYER
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two rear brake lines were leaking/rust. both brake line has been replaced. both rear wheels have been bled several time, no more air in the lines. still have very soft pedal. get very close to the floor. please note that sometimes the pedal got normal then suddenly goes very soft again and goes very near to the floor.

i did not see any leak around the master reservoir. fluid in the reservoir does not dropped since rear brake line has been replaced but brake pedal goes too close from the floor, no more air in the rear brake line. brake fluid is new as we have used around 800 ml while bleeding the rear wheels.

any tips or advice?
Apr 12, 2017 at 7:27 PM
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CARADIODOC
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Two common things to look for. If the vehicle has anti-lock brakes, and the master cylinder's reservoir ran empty, you will likely need a scanner to access the ABS Computer and command it to open the valves so some chambers can be bled. Many newer scanners have the procedure built into the software, and you just follow the steps displayed.

The second thing for any vehicle more than about a year old is the master cylinder was likely damaged the first time the brake pedal was pushed all the way to the floor. Crud and corrosion build up in the lower halves of the bores where the pistons do not normally travel. Pushing the pedal over half way to the floor runs the rubber lip seals over that crud and can rip them. That results in a slowly-sinking brake pedal or one that does not build pressure, and that often takes two or three days to show up.
Apr 12, 2017 at 7:51 PM