Brake pedal goes to the floor while applying brakes slowly.

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

6 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.

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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Tuesday, September 10th, 2013 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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Saturday, September 21st, 2013 AT 4:07 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, May 28th, 2018 AT 5:53 AM
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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Wednesday, May 30th, 2018 AT 11:15 AM
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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Saturday, June 2nd, 2018 AT 8:30 AM
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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Saturday, June 2nd, 2018 AT 12:37 PM

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