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Cranked up truck, pedal sank to the floor.

Tiny
ERIC LEEWRIGHT
  • MEMBER
  • 2008 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 195,000 MILES
I replaced my brakes (rear drums and shoes, front rotors. Pads I replaced about five months ago, left them on.) I wanted to flush some old fluid out so I went to bleed the lines. My front two caliper bleed screw were stripped and I ruined them even further over the course of two days trying to get them off with everything I had. Went and bought two new calipers. Replaced calipers, guide bolts, banjo bolt. (Calipers are on the correct side, bleeder on top) when I finished I bled the brakes. (RR, LR, RF, LF) until all visible air was out. (Went through two bottles of fluid) Hopped in truck and felt pedal with truck off. Felt nice and solid. I was feeling good. Cranked up truck, pedal sank to the floor. Not good. Bled two more times all the way around to be sure. No luck. Took to shop. They bled forever. No better. They said either master cylinder or booster. I argued about the booster because pedal was soft and not rock solid. I pulled my booster line off after I limped it home and heard a heck of a vacuum release. So I assumed booster was good. Decided to replace master as I suspected a busted seal. (Take to mind I had no issues other than a slightly spongy pedal before all of this work). Took master out and sure enough the front seal closest to the booster was frayed and torn all the way around. Good right? I bench bled the new master, installed it to the booster and bled the lines at the master. I then bled all four wheels again, just shortly checking for air. Hop in truck and pedal still sank to the floor. This is where I am at. I do have a new strange symptom now. I was in my driveway and drove the truck back and forth, five feet or so applying the brake and a couple of those times the brakes locked on when in drive with no throttle and it actually pulled to the right once when I pulled forward. I did one last check by pulling the master off the booster (lines still attached) and felt the piston was resting against the snap ring (as in it hadn’t gotten stuck in the depressed position). I’m just asking for help now because I’m now getting confused as to what could be going on.
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Wednesday, April 17th, 2019 AT 12:45 PM

38 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
Welcome to 2CarPros. I would suspect there is air in the lines. This guide 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 this guide and report back.
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Wednesday, April 17th, 2019 AT 3:23 PM
Tiny
ERIC LEEWRIGHT
  • MEMBER
  • 2 POSTS
That was it thanks for the guide it helped me find the problem all set! This site is amamzing
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Wednesday, April 17th, 2019 AT 5:22 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
Nice work, we are here to help, please use 2CarPros anytime.
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Friday, April 19th, 2019 AT 1:36 PM
Tiny
FYREMAN44
  • MEMBER
  • 1 POST
  • 2008 CHEVROLET SILVERADO
  • 6.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
I have changed all my calipers and bled the system until all new fluid came out of each. When the truck is off the pedal does become hard. But once the truck Is on the pedal is very soft and almost goes to the floor. If I pump the pedal as I drive it does built some pressure but not enough as I believe it should be. The truck stops but not as it should or fast enough. Do I need to re-bleed the system or the ABS system?
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Monday, February 22nd, 2021 AT 4:36 PM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

You need to pressure bleed the system. Using someone's foot or vacuum is not enough to pull out the air.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

The ABS needs to be done as well. You need a scan tool to do the automated bleed sequence for the ABS.

Roy
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Monday, February 22nd, 2021 AT 4:36 PM (Merged)
Tiny
GREG SCHULZ
  • MEMBER
  • 1 POST
  • 2007 CHEVROLET SILVERADO
  • 5.8L
  • V8
  • 4WD
  • AUTOMATIC
  • 225,000 MILES
No check ABS comes on on dash. No fuse issues. I’m at a total loss. Thought it was master brake cylinder but I just replaced it a year ago.
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Welcome to 2CarPros.

If there are no leaks or fluid loss, it has to be the master cylinder has failed again. Take a look through this link:

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

If you read through that and determine it is the MC, here is a link to help with replacement:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

_______________________________________

I attached an exploded view of the MC for you to see. Honestly, if there are no leaks and the fluid remains full, this is my first suspect.

Let me know if you have questions or need help.

Take care,
Joe
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
GENERAL.MOTORS
  • MEMBER
  • 21 POSTS
Check for faulty caliper, may piston won't move
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Honestly, if you have a stuck piston, that won't cause the brake pedal to drop to the floor.

Let me know what you find.

Joe
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
GENERAL.MOTORS
  • MEMBER
  • 21 POSTS
Hello jakob, I faced the same problem and noticed that one piston won't move, changed it and the brake pedal start to be normal
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+1
Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
It went to the floor? In my mind I can't see how that would happen. Not saying it couldn't.
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
DAVEERZ17
  • MEMBER
  • 1 POST
  • 2007 CHEVROLET SILVERADO
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 175,000 MILES
I replace the front brake pads. I have also replace the master cylinder. I have bled the brake system. Still the brake pedal goes to the floor very easy with or without the truck running.
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This could be a problem with air in the system, Double check that all the air has bled out of the system. I have also included a link below for you to go to.

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

I have also included a factory troubleshooting guide for you down below as well. Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
BROWN80204
  • MEMBER
  • 3 POSTS
  • 2007 CHEVROLET SILVERADO
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 112,000 MILES
Replaced entire brake system. No air in system, clear fluid when bleeding. Pedal goes to floor when engine is on.
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Was the master cylinder replaced? I just went through this same situation today with a trailblaizer. It was the master cylinder.

Take a look through this link:

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

Let me know. Also, let me know what prompted all the brake work and if the master cylinder was replaced, was is a new or re-manufactured part.

Take care,
Joe
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
BROWN80204
  • MEMBER
  • 3 POSTS
Started with a new rear axle shaft and new suspension parts. Master cylinder and power booster all new.
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
If it is new, then the only thing I can think of is the ABS needs to be bled. It requires a scan tool. Take a look through this and let me know if you have the tools to do it. Note that a standard bleed procedure is required before doing this. You have already done that.

If this doesn't help, I have a feeling you got a bad master cylinder.

If your truck has the vehicle stability enhancement, let me know. There is a different procedure.

____________________________

2007 Chevy Truck Silverado 1500 2WD V6-4.3L
(W/O JL4)
Vehicle Brakes and Traction Control Hydraulic System Brake Bleeding Service and Repair Procedures Antilock Brake System Automated Bleed Procedure (W/O JL4)
(W/O JL4)
Antilock Brake System Automated Bleed Procedure (Without JL4)

Notice: When adding fluid to the brake master cylinder reservoir, use only Delco Supreme 11(R), GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container. The use of any type of fluid other than the recommended type of brake fluid, may cause contamination which could result in damage to the internal rubber seals and/or rubber linings of hydraulic brake system components.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice.

Important: This procedure may be performed on all vehicles EXCEPT those equipped with option code JL4, Vehicle Stability Enhancement System (VSES).

Important: The base hydraulic brake system must be bled before performing this automated bleeding procedure. If you have not yet performed the base hydraulic brake system bleeding procedure, refer to Hydraulic Brake System Bleeding (Manual) Hydraulic Brake System Bleeding (Pressure) before proceeding.

1. Install a scan tool to the vehicle.
2. Start the engine and allow the engine to idle.
3. Depress the brake pedal firmly and maintain steady pressure on the pedal.
4. Using the scan tool, begin the automated bleed procedure.
5. Follow the instructions on the scan tool to complete the automated bleed procedure. Release the brake pedal between each test sequence.
6. Turn the ignition OFF.
7. Remove the scan tool from the vehicle.
8. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11(R), GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.
9. Bleed the hydraulic brake system. Refer to Hydraulic Brake System Bleeding (Manual) Hydraulic Brake System Bleeding (Pressure).
10. With the ignition OFF, apply the brakes 3-5 times, or until the brake pedal becomes firm, in order to deplete the brake booster power reserve.
11. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.
12. If the brake pedal feels spongy, repeat the automated bleeding procedure. If the brake pedal still feels spongy after repeating the automated bleeding procedure inspect the brake system for external leaks. Refer to Brake System External Leak Inspection. See: Hydraulic System, Brakes > Component Tests and General Diagnostics
13. Turn the ignition key ON, with the engine OFF; check to see if the brake system warning lamp remains illuminated.
14. If the brake system warning lamp remains illuminated, DO NOT allow the vehicle to be driven until it is diagnosed and repaired. Refer to Symptoms - Hydraulic Brakes. See: Hydraulic System, Brakes > Symptom Related Diagnostic Procedures > Symptoms - Hydraulic Brakes
15. Drive the vehicle to exceed 13 km/h (8 mph) to allow ABS initialization to occur. Observe brake pedal feel.
16. If the brake pedal feels spongy, repeat the automated bleeding procedure until a firm brake pedal is obtained.

______________________________

Joe
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
BROWN80204
  • MEMBER
  • 3 POSTS
Thank you, we will try this hopefully this weekend.
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
You are welcome. If you have a chance, let me know if it helped.

Take care,
Joe
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Monday, February 22nd, 2021 AT 4:37 PM (Merged)
Tiny
MDBIRD1991
  • MEMBER
  • 2 POSTS
  • 2006 CHEVROLET SILVERADO
  • 4.8L
  • V8
  • 2WD
  • AUTOMATIC
  • 168,352 MILES
I found that the master cylinder was leaking fluid into the brake booster, I replaced both the master cylinder and brake booster, and have bled the brakes. When the vehicle is not running, the brake system feels to operate normally. However, once I start the engine, the brake pedal easily pushes straight to the floor, and you can hear a hissing near the brake booster/master cylinder area, as if the booster is just sucking in air.
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Monday, February 22nd, 2021 AT 4:38 PM (Merged)

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