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I replaced the Master cylinder my brake pedal go to the floor?

Tiny
TODD VILLANUEVA
  • MEMBER
  • 2007 HYUNDAI TUCSON
  • 1.8L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 190,000 MILES
Hello,
I replaced rotors and pads and calipers that were clearly faulty. I replaced the master cylinder, bench bled it, bled the brakes with the bleeder screw and a hose into a plastic bottle of clean brake fluid, but the brake pedal still goes to the floor when the car is running. The brake booster seems good because when I have the car running and the brake pedal pushed down, I will turn the car off and the pedal lifts back up against my foot with good pressure. There are also no leaks anywhere. Is it possible that another caliper is letting air in some how and I do not know it? How would I find that out? Should I just replace the remaining calipers that are old and original to the car and then see what happens?
Thanks for any help.
Todd Villanueva
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Wednesday, February 22nd, 2017 AT 3:31 PM

3 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,752 POSTS
I would suspect there is air in the lines. These guides can help you fix it.

https://youtu.be/w7gUsj2us0U

and

https://youtu.be/WDxvEQrMkBg

and

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please run down these guides and report back. I suspect your car has anti-lock brakes. If it does, and you let the master cylinder run empty while the calipers were off, yo will likely need a scanner to command the computer to open the valves in the hydraulic controller so air can be expelled from some of the chambers. To prevent this next time, use a stick from the seat to hold the brake pedal down an inch or two. The lip seals on the master cylinder will stop the brake fluid from running out.
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Wednesday, February 22nd, 2017 AT 3:43 PM
Tiny
TODD VILLANUEVA
  • MEMBER
  • 2 POSTS
Do you mean if I had the master cylinder off the car and a caliper off the car at the same time? I did not let the lines run dry when a caliper was off.
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Wednesday, February 22nd, 2017 AT 3:52 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,752 POSTS
You do not have to have both off at the same time. With just one caliper disconnected, brake fluid will siphon out of the reservoir, especially if the cap is loose. It is also possible for the fluid to be held in the reservoir from vacuum when the cap is tight, but it can run out of the line all the way up to the hydraulic controller.

You still did not say if you have anti-lock brakes, but it sounds like the controller needs to be energized to bleed the air out.
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Wednesday, February 22nd, 2017 AT 5:42 PM

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