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Brake pedal goes to floor when car is running?

Tiny
THETANK
  • MEMBER
  • 1999 CHRYSLER LHS
  • 3.5L
  • V6
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
Replaced all 4 calipers, master cylinder and power booster. Bleed brakes. With car off good pedal. Start the car and pedal goes to floor.
Thursday, April 27th, 2023 AT 3:35 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Hi,

Did you bleed the ABS? The ABS portion of the brake system must be bled separately using a bidirectional scanner.

Take a look below. I attached the directions. Let me know if this is something you can do or have done.

You likely have air in the system.

Let me know.

Joe

See pic below.
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Friday, April 28th, 2023 AT 11:39 PM
Tiny
THETANK
  • MEMBER
  • 5 POSTS
Bled the ABS system four times. Pedal is a little better but still goes too low.
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Saturday, April 29th, 2023 AT 9:42 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Hi,

Did you follow the sequence listed in the directions? It indicates a standard bleed, then the ABS, then a standard bleed again.

What you are describing is either air in the system or a bad master cylinder. I've seen situations where the push rod between the booster and MC wasn't properly seated causing similar issues. Everything went back together easily, correct? Also, before installing the new master cylinder, was it bench bled?

Let me know.

Joe
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Saturday, April 29th, 2023 AT 7:21 PM
Tiny
THETANK
  • MEMBER
  • 5 POSTS
Yes, bench bleed master cylinder and went together easy and adjusted the free play on the booster. When the car is not running there are awesome brakes. Plugged the vacuum line at the intake and running without booster it stops good. Hook vacuum back to booster and they go to floor.
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Sunday, April 30th, 2023 AT 2:42 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Hi,

If the booster was causing the issue, the brakes would lock up if they went to the floor. That isn't the case. Are you able to pump up the brake pedal if the booster is connected? I ask because all the booster does is provide assistance (which makes it easier to press).

Let me know.

Joe
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Sunday, April 30th, 2023 AT 6:30 PM
Tiny
THETANK
  • MEMBER
  • 5 POSTS
It does not pump up.
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Monday, May 1st, 2023 AT 3:00 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Hi,

When you bled the ABS, was it done via the data link connector with a bidirectional scan tool? That's the only other thing that makes sense.

Joe
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Monday, May 1st, 2023 AT 8:29 PM
Tiny
THETANK
  • MEMBER
  • 5 POSTS
Yes, also tried new master cylinder with no changes.
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Saturday, May 6th, 2023 AT 9:02 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,973 POSTS
It isolates the problem gently take four vise grips and close off the flex hoses that go to the wheels to see if the pedal stays hard, if so the problem is a the wheels if not the problem will be with the master. Did you bench bleed the master, if not this can be the problem here is a guide and a video to help us with the problem. Also, when you say you bled the ABS did you open the ABS valves?

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

and

https://youtu.be/nQRnKyVyMuQ

and

https://youtu.be/WDxvEQrMkBg

Please go over these guides and report back.

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Sunday, May 7th, 2023 AT 9:58 AM

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