Brake pedal goes to the floor?

Tiny
ASEMASTER6371
  • EXPERT
Did you replace the master cylinder?

Roy
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
ANGIGREER
  • MEMBER
Well, I just realized that I don't know right from left so maybe that is the problem. Will try bleeding in the right sequence.
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
ASEMASTER6371
  • EXPERT
Okay, did you replace the master cylinder?

Roy
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
ANGIGREER
  • MEMBER
Did not replace master cylinder. We tested it and it seems to be working fine.
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
ASEMASTER6371
  • EXPERT
How did you test it? You have no pressure to a couple of wheels.

Roy
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
JOHNEDWARDS
  • MEMBER
  • 1996 FORD F-150
  • 240,366 MILES
Depress brake pedal holds good let off a little pedal goes to floor.
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
That's the classic symptom of a failing master cylinder. You're still holding pressure on it, but you're modulating that pressure.

The clue to this "internal leakage" is you're not losing brake fluid. This article explains it better:

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

Here's a trick I've used since the '80s to avoid having to bleed at the wheels.

When you replace the master cylinder with two steel lines, loosen the line nuts a little, remove the mounting bolts to the power booster, pull the master cylinder forward, then use it as a handle to bend the steel lines up a little. That will keep the fluid from running out of the lines.

Remove the two lines all the way, then remove the master cylinder. Brake fluid eats paint, so be careful to not allow any to drip onto the truck.

Screw the two lines into the new master cylinder that has been bench-bled, then use it to bend those lines back down to their normal shape. Bolt it to the booster, then snug one of the line nuts. Have a helper slowly push the brake pedal half way to the floor. It should take about 15 seconds to do that. You'll see bubbles coming out by that nut. Snug the nut, then holler to the helper to quickly release the pedal.

Do that a second time, and perhaps a third time, until you see only clear fluid with no bubbles coming out, then do that for the other line. By pushing slowly, fluid will get pushed down the lines, and air will float back up. By releasing the pedal quickly, the fluid rushing back will wash the air back up into the reservoir with it. This can even work when working on the car by yourself, just keep the line nuts tight.

This wondrous trick might not work on Fords that have four lines at the master cylinder. You still don't have to bleed at the wheels, but it can take a little longer for all the air bubbles to be expelled into the reservoir.

It's good practice to never push the pedal over half way to the floor, although it won't matter with a rebuilt master cylinder. Once they get to be about a year old, crud and corrosion build up in the lower halves of the bores where the pistons don't normally travel. Pushing the pedal to the floor, like most do-it-yourselfers do, runs the rubber lips seals over that crud and can rip them. That results in a slowly-sinking brake pedal, and that often doesn't show up until two or three days later.

When you're replacing calipers or wheel cylinders, a lot of people make misery for themselves by allowing the master cylinder to run empty, then they have to bleed the entire circuit. Often a scanner is needed on anti-lock brake-equipped vehicles to open some of the valves so the chambers can have the air expelled. To avoid that, use a stick between the seat and brake pedal to hold the pedal down an inch or two. Gravity won't be strong enough to pull the fluid past the lip seals.

Also, when you do bleed at the wheels after replacing the master cylinder, any air in the lines gets pushed down to the wheels, and if the vehicle has anti-lock brakes, it's common on most designs for that air to become trapped in the hydraulic controller. That's where you need the scanner to do the bleeding procedure. I find it much easier and faster to just avoid pushing that air down there.

Here's another article you find useful:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
CHARLEP
  • MEMBER
  • 1990 FORD F-150
  • 5.8L
  • V8
  • 4WD
  • AUTOMATIC
  • 140,000 MILES
If I pump I get brakes. Took of wheel and saw that the diamond looking pin is out on drivers side could this be the problem? The pad look good. And do I need to bleed them?
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
ASEMASTER6371
  • EXPERT
Good evening,

It does sound like you have air in the system but I think more that you need a master cylinder.

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

Yes, it needs to be bled.

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

Can you upload a picture of the piece?

Roy
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Wednesday, March 10th, 2021 AT 11:29 AM (Merged)
Tiny
F1501988
  • MEMBER
  • 1988 FORD F-150
  • 5.8L
  • V8
  • 4WD
  • AUTOMATIC
  • 145,000 MILES
Basically just got the truck, had a leaking rear wheel cylinder. So I replaced both rear wheel cylinders, brake lines, brake shoes, then replaced both front axle bearings, front pads, and both calipers. I have bled the system several times, because I kept thinking I did not get all the air out. When I have pumped the brakes and bled them it would get to be a nice firm brake pedal. Now here s the problem, when I start the truck and apply not much pressure the brake goes to the floor and won t come back until I pull it up. So at a loss, don t want to keep replacing things, like booster, or master cylinder, and even found out that the truck has RABS (rear ABS).
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
This could be a number of things but it sounds like you replaced the common ones. Here is a guide that goes through this issue:

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

This is one of two things. First you either still have air in the lines or there is a leak. If you have no leak outside the system then we can still have an internal leak allowing the pressure to bleed off rather then being applied to the brakes.

If you have not replaced the master cylinder then this would be the most likely cause. I would take the lines off the master cylinder and cap the outlets and then press the brake pedal. If the pedal still goes to the floor then the master cylinder has a leak internally. If not, then the master cylinder is fine and we have an issue is further down in the system.

Let me know if you have questions about this and we can go from there. Thanks
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
F1501988
  • MEMBER
Thank you, do you need to bleed the ABS hydraulic unit? Oh, and I have checked for leaks any where in the system and nothing is apparent.
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
You only need to bleed the hydraulic unit if it is replaced. Once it is bled it is okay so this is most likely not the issue.

If you have no external leaks, I would go after the master cylinder. If you find it is the issue, just make sure you bench bleed it so that you don't damage it when trying to bleed it on the vehicle.
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
F1501988
  • MEMBER
Thanks, I need to get to the parts store and pick up some bolts to plug the master cylinder and test it, but might get the master cylinder anyway. Just trying to figure it out, because we got it for a second vehicle and haven t even got to put it on the road. Plus, on a fixed income at my age. So really want to thank you, and Ill let you know. Oh, being I do this by myself, been using the jar method for bleeding, should I just try the gravity method.
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
Sounds good. If you get bolts just make sure they are not too long or you will crack the master cylinder. Just use a whole bunch of washers if needed. You can compare the depth to the depth of the lock nut on the actual line. It should be no longer then the threads of the nut on the line.

Gravity bleeding can work but it doesn't always get all the air out. You will need to bench bleed the master cylinder as that will gravity bleed.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
F1501988
  • MEMBER
Hoping to get to the store on Saturday, figure I ll get the bolts and probably get the master cylinder. I don t get there to often due to transportation. So that way if it turns out to be the master cylinder I ll have it to change out, if I don t need it then I can bring it back. Thanks for the bolt size information, didn't think of that. To bleed the brakes do I need to take the spring out of the ABS unit. I seen a thing on YouTube that said you need to take the spring out, and I actually have no idea. But I can take it out if needed. Thanks
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
No. I don't believe you do. I am not sure what you saw on the internet but once the ABS is bled it doesn't need to be done again. If you can post a link to that video, I will take a look and see what they were saying.

Thanks
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
F1501988
  • MEMBER
It s on YouTube, (how to bleed brakes with RABS ( Ford ABS ). When I was checking to see if there was another way to bleed brakes. Now when I bleed the brakes, start passenger rear, driver rear, passenger front then do I bleed ABS valve? Then driver front?
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
Okay. I will check that out but I think I misunderstood with what you were saying earlier.

You are correct with needing to do the ABS valve but not in the process you stated. I attached the process from the manual.
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)
Tiny
F1501988
  • MEMBER
Hi Kenny, well put the new master cylinder in and bench bled it. Then I was going by the process sheet you sent, but not really getting any fluid out of the ABS valve. Is there a certain way? I even left it open and pumped the brakes and got very little fluid. I would say it has to have fluid somehow going through it because I bled the rear brakes okay. Could there be that much air in it? Thinking of trying to gravity bleed it and just hook a tube to it and crack it open, not sure what to try next.
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Wednesday, March 10th, 2021 AT 11:30 AM (Merged)

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