Changed the Master cylinder the pedal still goes to the floor

Tiny
PATCLARK
  • MEMBER
  • 2002 FORD F-250
  • 85,000 MILES
First noticed`this problem when a deer ran in front of me and I slammed on the brakes and they kinda stuck bringing me almost to a stop before they released. Naturally I avoided slamming on the brakes. Next thing (days later) it sounded like a stone or something was caught in the left front rotor. Later in the day I lost brake pedal travel partially then to the floor but never completely lost the brakes.

I pulled the tire and the rotor felt slightly held by the brakes but the pads and rotor were fine I beld the brake but it made no difference. Everything about the assembly is tight no bad bearings etc.

I have changed the master cylinder but it did not change a thing.
I still have some brakes but have brake pedal travel to the floor.
I have checked the vacuum for the booster and found it to be OK.
Is this a faulty vacuum booster or something else?
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Tuesday, September 27th, 2011 AT 12:38 AM

8 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
It sounds like you have an axle bearing that has gone bad and is causing an air gap between the brake rotor and brake pads. It will pump up but a short time later the brakes will be on the floor again.

Here is a guide so you can do some checking to confirm the problem.

https://www.2carpros.com/articles/how-to-replace-front-wheel-bearings-and-seals

and

https://www.2carpros.com/articles/bearing-hub-replacement

This can also happen when a caliper slide seizes. Check to make sure the calipers can move freely on the slides.

Here is a guide that shows you how to service the slides.

https://www.2carpros.com/articles/how-to-replace-front-brake-pads-and-rotors-fwd

If the brake hoses are leaking here is a video that will show you how to replace them.

https://youtu.be/xMS8Xy4Xz1U

Let me know what you find.
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Tuesday, September 27th, 2011 AT 2:13 AM
Tiny
PATCLARK
  • MEMBER
Perhaps I should have noted that I have no leaks the fluid level does not go down; of course except except when I bled the lines.

I do hear an air sound when the brake pedal is depressed inside the booster however faint. I am going to order one today unless you guys have another idea.

Thanks
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Tuesday, September 27th, 2011 AT 11:32 AM
Tiny
WRENCHTECH
  • EXPERT
The booster typically wont make the brake pedal sink to the floor.

Here is a guide that can help you more i think.

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

You might have a bypassing master cylinder which is most common in some rare instances, it happens within the ABS unit.

Here is a guide to replace the master

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

Please let us know what you find.

Cheers

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Tuesday, September 27th, 2011 AT 12:42 PM
Tiny
PATCLARK
  • MEMBER
OK What do you suggest I do from here? I have replaced the master cylinder already bench bled it before installation. I would like to add that I do have brakes enough to stop the truck but no different than before I changed the master cylinder. The brakes remain at the end of travel which is where they ended up since this happened. They do not leak down they are just not there until the pedal is fully depressed. If I had a bypass would I not run out of brake pedal travel and consequentially brakes as well?

It was suggested that I drive the truck insane right? Well I did have some brakes so I decided to try it. I live on a big hill so I pulled it out onto a flat spot and went back an forth several times with the brakes improving every time until I felt OK taking it down our hill. Got brave enough for a road test and long story short I will be taking the truck to work tomorrow.

I still have this issue of the brakes sticking on when I brake real hard then releasing (some kind of delay) but it happened less and less as we drove and braked intermittently.

Also the dragging noise that came from the drivers side brake that was also there before I replaced the MC seems to be lessening as well. I will report back tomorrow after more of this testing and checking out how things are.I am just not convinced I have found the root cause of this problem.
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Tuesday, September 27th, 2011 AT 11:22 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Before you pull out tomorrow make sure you have a good pedal. If you were hearing a drag on one of the front bearings the noise can come and go.

On the brake lines make sure it isn't ballooning when you depress the brake pedal. I could be wrong, but those hoses go bad. They can cause the caliper to stick on of the fluid doesn't return due to internal damage in the hose.

Also, they can expand when you hit the brakes. Thus yo have a low pedal. Please double check the side that you heard the noise from.
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Wednesday, September 28th, 2011 AT 1:09 AM
Tiny
CJ MEDEVAC
  • EXPERT
This is sorta the way i bench bleed on the vehicle

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

this can be done on the vehicle (my preference) using two people, one pumping and one monitoring the master cylinder. i wrap string loops around the little hoses, and tie a knot, as to keep the tubes from blowing off of the plastic adapters.

i take it one step further, by squeezing the little hoses with my fingers (as if i were a check valve) the very slow pumping of the pedal will push the fluid into the reservoir, by my pinching, but will not allow it to suck air/fluid back into the mc (constantly an outward flow), as you will see happen in the beginning of this video....my way makes air purge faster, but if you did not tie the hoses to the adapters--they will blow loose (lots of adjectives will be used, and your eyes may burn!)

is this sorta what you did, off the vehicle?

this is the way i bleed (people often sorta do it wrong! on some newer stuff, other steps may be involved, the other guys may add that in, if needed, this way has always worked for me!)

i have tried the vacuum pump way, and also the line attached to a bleeder valve submerged in a cup of brake fluid........never satisfactory results for me!

this is the way i was taught

keep fluid in the reservoir at all times/ constantly checking!

start with furthest out wheel cylinder, from the master cylinder, working to the closest (rr, lr, rf, lf)

2 people, one pumping, other bleeding and refilling

1-man breaks bleeder loose (so it ain't so tight)-snugs it back yells, "pump it up"

2 man-pumps 6-8 times (yells "pumping") then holds pedal--yells, "holding" (never lets up, until told to)

1-man cracks bleeder...air/ fluid spurts out

2-man yell, "floor", just before the pedal, actually hits the floor

1-man tightens the bleeder....while it is still spurting out (not after it stops...or it will suck air back in).....then yells, "okay---pump it up"

after you get a rhythm going and your pumping man, is "trained", the lingo sorta turns into

1 man "ok!"

2 man "ok!"

and so on!

process starts over, until you are satisfied the air is purged out

you should have "drum brakes" already adjusted outward, before you do the bleeding procedure.

i have seen dummies break open the bleeders, and just start pumping away, then shut 'em......not good!

maybe you have done all of this--maybe you just didn't know---i figured i'd sling it out, just in case....many times we "assume" the other party is doing things correctly...then chase our tails, looking for non-existent, other possibilities
xbleeding

the medic
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Wednesday, September 28th, 2011 AT 4:48 AM
Tiny
PATCLARK
  • MEMBER
Thanks guys for your thoughts. The bleeding instructions are great! I did take the truck to work today and the brakes seem fine. It rained like crazy all day so I couldn't get a good take but I could not feel any drag from the left front tire I was going to check the brakes to see if they hung up again when I slammed them real hard but was unable due to a new development.

I was going to bleed the brakes again as well when I got home tonight as I did have to add some brake fluid after driving it but guess what?

It was all fine when I took it for a test drive last night and the pedal went to the floor again so I checked the axle bearing and it was loose. Once I replaced it everything was fixed, you guys are so smart! Thanks 2Carpros
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Wednesday, September 28th, 2011 AT 11:54 PM
Tiny
KEN
  • ADMIN
Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help

Cheers, Ken
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Wednesday, September 27th, 2017 AT 4:49 PM

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