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Brakes pedal sinks to the floor

Tiny
MARK WI
  • MEMBER
  • 2008 DODGE AVENGER
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 79,500 MILES
Brake pedal not holding, it sinks to the floor. I have change the brake master cylinder but did not fix. I have bleed the brake system, it has improve little bit, in the sense of the pedal holding at certain point, but if constant pressure is kept on the pedal it will still sink to the floor. Do a have a problem with my brake booster? Or should I bleed more the brake system? Or might be some other problems?
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Thursday, March 8th, 2018 AT 5:15 AM

9 Replies

Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
Did you also bleed the master cylinder? 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.
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Thursday, March 8th, 2018 AT 7:05 AM
Tiny
MARK WI
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  • 7 POSTS
According to the service center they did bleed the master cylinder. But, not sure.
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Thursday, March 8th, 2018 AT 10:19 AM
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
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A service center? If this was a mechanical shop, I am sure they would know to bleed the master cylinder. Was it this service center that also bled the brake system?
Is this service center a automotive shop/garage with mechanics?
Does the brake warning light come on when the brake pedal is pressed down? If so, there is still air in the brake fluid system.
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Thursday, March 8th, 2018 AT 10:31 AM
Tiny
MARK WI
  • MEMBER
  • 7 POSTS
It is a Dodge service center, but I went to another workshop for the wheel brake bleeding, as I was thoughtful if they have bleed the master cylinder as after they return my car I saw the brakes was the same. They insisted of changing the brake booster as well. As the mechanic at the other workshop was bleeding the brakes I notice old brake fluid was still in the line but in the reservoir was with new clean brake fluid. After they bled the brakes I notice a change of the brake pedal, but still it sinking to the floor. I am getting the engine fault light, it comes and go, do not know if it is related with the problem I am having.
Do you think I should bleed the brakes more or flush my brake system? Maybe the brake fluid is old? Or is the brake booster the reason?
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Thursday, March 8th, 2018 AT 11:58 AM
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
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You should be able to rule out the brake booster by pumping the brake pedal several times with the engine off to deplete all the vacuum in the booster. Then press the pedal down one last time and if it still goes to the floor than it is not the booster.
If the brake warning light comes on when pressing down the brake pedal with the key on then there is still air in the system.
This is the proper brake bleeding sequence, so if this sequence wasn't used it will have to be bled again in this order:
Left rear wheel.
Right front wheel.
Right rear wheel.
Left front wheel.
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Thursday, March 8th, 2018 AT 12:31 PM
Tiny
MARK WI
  • MEMBER
  • 7 POSTS
Will confirm if it is not the brake booster. They will do the proper brake bleeding sequence. Hopefully it will solve my issue.
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Thursday, March 8th, 2018 AT 1:02 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,356 POSTS
It sounds like you have air stuck in the ABS valve you will need to take it to a shop that can open the valves with the ABS scanner and then bleed the system.

Check out this guide:

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

Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Monday, March 12th, 2018 AT 12:21 PM
Tiny
RON_6751
  • MEMBER
  • 2 POSTS
  • 2008 DODGE AVENGER
  • 2.7L
  • V6
  • FWD
  • AUTOMATIC
  • 160,000 MILES
Brake pedal creeps down when pushed down with engine running. I have replaced the front and rear pads and machined both rotors front and rear and have replaced the master cylinder. I have bleed all the brakes and still have a low pedal, but when engine is off the pedal does not creep. Curious no? But once started the pedal drops down. Is it possible that air is trapped in the front of the master cylinder since the master sits at an angle or what?
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Monday, March 1st, 2021 AT 11:19 AM (Merged)
Tiny
CARADIODOC
  • MECHANIC
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A better suspect is the car has anti-lock brakes, and the hydraulic controller needs to be bled. That usually requires a scanner to command the computer to open some valves so the chambers can be bled.
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Monday, March 1st, 2021 AT 11:19 AM (Merged)

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