Brake pedal goes to the floor while applying brakes?

Tiny
MBUCKHAN
  • MEMBER
  • 2003 FORD F-150
  • 145,000 MILES
Starting out I have a brake pedal that stops the truck, but when I sit at a light the brake pedal does all the way to the floor and the truck inches forward. The master cylinder has been replaced to try and correct the issue, all four wheel seals were checked and no leaks found, all brake lines were bled and have no leaks and the brake fluid stays at the proper level, so the system does not have a leak. Could the ABS box be the issue and what in the ABS box would cause this problem?
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Tuesday, September 10th, 2013 AT 11:55 AM

51 Replies

Tiny
HMAC300
  • EXPERT
It can take up to 3 qts to bleed brakes on an abs system was the master bled prior to installation? if not that is your problem you'll need to bleed again preferably with a power bleeder or vacuum. here is a test to do on abs unit.

It sounds like the master is bad these guides can help us

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

and

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

Probably abs hydraulic unit. If it is 2wal you should find a rubber cap on one end of the release valve. Take the cap off and stick a straightened paper clip in the hole. Have someone push on the brakes, if it pushes your paper clip then the 2wal valve is bad. Good luck
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Monday, January 6th, 2020 AT 12:05 PM
Tiny
CJ MEDEVAC
  • EXPERT
The master cylinder could have a so called "internal leak", where as the plunger inside is not sealing in the bore 100% fluid slowly leaks by this can happen even with a brand new unit.

Rebuilding or replacing the master cylinder is the fix

The Medic
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Monday, January 6th, 2020 AT 12:05 PM
Tiny
CHRISTOPHER NULL
  • MEMBER
So I have been reading lots and lots of posts on this issue. How can 4 or 5 M/C be bad in a row? That just seems unlikely. My best guess so far is ABS unit or pump.
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Monday, January 6th, 2020 AT 12:05 PM
Tiny
KEN
  • ADMIN
Yes this problem is common the ABS valves need to opened using a scanner and then bleed the system.
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Monday, January 6th, 2020 AT 12:05 PM
Tiny
CHRISTOPHER NULL
  • MEMBER
My friend that works at a garage found this on the Mitchell's manuals site for a 2000 F150

If equipped with the four wheel anti-lock brake system and the Hydraulic Control Unit (HCU) has been replaced or is suspected of containing trapped air; bleed the brake system using the procedure below. Conventional brake system bleeding cannot remove the air trapped in the lower portion of the HCU. If a spongy or sagging brake pedal is present and air in the hydraulic control unit is suspected, use the following procedure:

1. Bleed the brake system as outlined in the conventional bleeding procedure.
2. Connect a New Generation Star (NGS) tester or equivalent scan tool, to the serial data link connector below the instrument panel as though retrieving codes.
3. Make sure the ignition switch is in the RUN position.
4. Follow the instructions on the NGS screen. Verify correct vehicle and model year go to the "Diagnostic Data Link' menu item, choose ABS Module, choose "Function Tests", and choose "Service Bleed."

5. Bleed the right-front wheel as follows:
---A. Open the caliper bleed screw and pump the brake pedal for 3 seconds. Repeat the procedure again.
---B. When the fluid runs clear, begin the program and continue to pump the brake pedal.
---C. Continue bleeding for approximately 1 to 2 minutes after the program ends and then tighten the bleed screw.
6. Repeat the bleeding procedure to the left-front, left-rear and finally the right-rear wheel.
7. Remove the pressure bleeding device and adjust the brake fluid level.
8. Road test the vehicle and check for proper brake system operation.

This is what you have to do. Period. If you want the brakes to bleed off properly
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Monday, January 6th, 2020 AT 12:05 PM
Tiny
KEN
  • ADMIN
Good find, well put. Use 2CarPros anytime, we are here to help. Please tell a friend.

Cheers, Ken
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Monday, January 6th, 2020 AT 12:05 PM
Tiny
JMARES0502
  • MEMBER
  • 2003 FORD F-150
  • 4.2L
  • 190,000 MILES
When I'm park my break peddle is hard on my 2003 ford f150 truck when I'm driving it goes to the floor and my abs is on. On the dashboard
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Thursday, September 24th, 2020 AT 11:36 AM (Merged)
Tiny
ASEMASTER6371
  • EXPERT
Good morning,

Is the master cylinder full? Make sure the fluid level is correct.

This could be either a bad master cylinder of a brake fluid leak. Did you check under the truck for any leak?

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

You could try bleeding the system and see if there is any air in the system but if there is, it comes from somewhere.

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

Most likey, the master cylinder is the issue and must be replaced. Then the system will have to be flushed and bled out with a pressure bleeder.

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

The ABS light may be on due to this issue but there is a fault code stored in the system for the ABS system. I need this code to narrow that area of failure. A parts store will read it for free for you. Let me know the code and I can help a lot more.

https://www.2carpros.com/articles/abs-warning-light-on-easy-repair-guide

Roy
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Thursday, September 24th, 2020 AT 11:36 AM (Merged)
Tiny
HENRY DAVIS
  • MEMBER
  • 2003 FORD F-150
  • 5.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 90,000 MILES
I changed; master cylinder, all four calipers, bled system, but no brake pedal.
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Thursday, September 24th, 2020 AT 11:36 AM (Merged)
Tiny
HEYMAN1104
  • EXPERT
Did you bleed the master cylinder before installing it? If not, then you will need to take it off and do it, reinstall it, and then re-bleed the calipers. Look at step three in this guide: https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Good luck and let us know.
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Thursday, September 24th, 2020 AT 11:36 AM (Merged)
Tiny
ALLEN FITTS
  • MEMBER
  • 2001 FORD F-150
  • 5.4L
  • 6 CYL
  • 2WD
  • MANUAL
  • 180,000 MILES
I changed out my brake pads, bled the brake lines, and my brake pedal is still going to the floor. I have checked fluid levels, and are all full. I have no leaks at any given point.
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
At this point the issue is most likely the master cylinder leaking internally.
Also it could a brake line issue that is swelling when you press the pedal. However, this will normally cause a soft pedal and not going to the floor. So I would think the master cylinder is leaking internally.

If you take the lines off and cap the outlets of the master cylinder then press the pedal if it still goes to the floor then you know if it is leaking internally because you have eliminated the rest of the braking system.

Let me know if you have questions. Thanks
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
WICKEDBRAKES
  • MEMBER
  • 2001 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 100,000 MILES
I have replaced master cylinder, bench bled twice, brake hoses on the front, new brake pads, new booster, bled the system numerous times, and there are no leaks. Yet the brake pedal still goes to the floor. Pumping the brakes will build up some pressure but will go down. I see several articles regarding adjustment of the pushrod in the booster and that there is a special tool(or by trial and error). What is this tool and where do you get it? Are there other things I should consider before spending time removing the master cylinder over and over. From what has been posted, its a crap shoot.
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
HMAC300
  • EXPERT
You can try power bleeding the system as there may still be air in abs unit. Otherwise a pro will need to use his scanner to open valves on abs then bleed it. IT can take 3 qts or more to bleed it
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
2CARPROS-ARCHIVES
  • MEMBER
  • 2001 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 77,000 MILES
2001 Ford F-150 4x2 mileage: 77,000. The brake pedal is pulled to the floor on its own when the brake is just started to be applied. With no pressure on the brake, the truck stops and the pedal must be pulled back by foot to release. Could the brake booster be causing this? What is the problem?
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
2CARPROS-ARCHIVES
  • MEMBER
Sounds like the power brake booster is faulty.
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
MICHAEL MCCALL
  • MEMBER
  • 2000 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 167,000 MILES
I get brake pressure when the truck is off as soon as I turn it on it goes straight to the floor. I already changed the master cylinder.
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
Did this start before you replaced the master cylinder? How did you bleed the air out? What led up to this problem? Do you have anti-lock brakes? Are the rear brakes disc or drum? Have you checked the brakes?
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
MICHAEL MCCALL
  • MEMBER
Yes I did it before I changed it, I bleed it with my friend I pumped the brakes he opened the valve, I do have anti lock, and I have drum brakes. I also put new brakes pads on the front and a new right front caliper.
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
The first red flag is when bleeding with someone pumping the brake pedal, at any time did they run the pedal all the way to the floor? If they did, most likely the master cylinder was damaged. Crud and corrosion build up in the lower halves of the bores where the pistons don't normally travel. Running the pedal all the way down runs the rubber lip seals over that crud and can rip them. That results in a slowly-sinking pedal at first, then no pedal at all, and that often doesn't start until two or three days later.

The next thing is a scanner is often needed on some vehicles with anti-lock brakes to open some of the valves in the hydraulic controller. There is no other way to bleed the air out of some of the chambers.

Check the adjustment of the rear shoes, and look for a rear lining that is broken / rusted off the backing plate. That will cause a good pedal one minute and a low pedal the next minute.
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Thursday, September 24th, 2020 AT 11:37 AM (Merged)

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