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Brake pedal goes to floor when engine NOT running

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Brake pedal goes to floor when engine NOT running

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  #1  
Old 01-17-2018, 10:18 AM
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Brake pedal goes to floor when engine NOT running

So after a lot of searching and reading, I cannot find a thread where the brakes go to the floor when the engine is NOT running. They never gain back pressure no matter how many times I pump and I don't see any leaks externally.. Can this be a bad MC? All fluids are correct level as well.

Also, the pedal goes almost to the floor when its running. Its like it doesn't start braking until about 1 inch from the floor.

Another thing I noticed is that if I hold the brake pedal down, I can only turn the steering wheel about a quarter turn then it locks up. As soon as I let the pedal go, the steering frees up.
 
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Old 01-17-2018, 10:34 AM
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It would help tremendously to know what the mystery vehicle is...
 
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Old 01-17-2018, 10:48 AM
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Sorry, it is a 2001 F-350 CC LB DRW Lariat LE 4X4 with the 7.3 and auto trans.
 
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Old 01-17-2018, 10:58 AM
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Your truck does not have a master cylinder. It operates off a hydroboost which also is linked to the steering. If power steering is low it can affect the hydroboost.
 
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Old 01-17-2018, 11:24 AM
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Uuhhhh, I'm almost positive they still have a MC. They just don't have a brake booster, it uses the hydroboost like you stated.
 
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Old 01-17-2018, 11:38 AM
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Your truck definitely a master cylinder it uses hydro boost instead of the vaccum boost so it doesnít have the vaccum booster mounted to the firewall.
 
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Old 01-17-2018, 01:38 PM
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Originally Posted by Mike189677 View Post
Your truck definitely a master cylinder it uses hydro boost instead of the vaccum boost so it doesnít have the vaccum booster mounted to the firewall.
Correct. I am leaning towards it being a bad MC but just wanted to see if anyone has had this problem. The steering locking up when braking is what is throwing me off..
 
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Old 01-17-2018, 06:35 PM
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Sounds like a hyroboost problem not a master cylinder problem to me with the steering locking up while on the brakes. Maybe thatís why your thrown off looking at the master cylinder.
 
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Old 01-17-2018, 07:38 PM
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Maybe I'll just change both lol. They are pretty cheap and not very hard to change.
 
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Old 01-18-2018, 02:01 AM
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Originally Posted by Campsta View Post
Maybe I'll just change both lol. They are pretty cheap and not very hard to change.
You could do that but you probably still have the same problem. I should have been more specific when I said I thought it was a hyroboost problem. Since both the steering and brakes are affected the power steering pump is the main suspect in my mind as it supplies hydraulic pressure to both the brakes and steering in the hydroboost system. How is the level and condition of the power steering fluid has it ever been changed though we are most likely past that point any leaks anywhere in the system?
 
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Old 01-18-2018, 02:36 AM
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How old are your brake pads? If they're worn, that would explain the low pedal. This might be a good time for a brake system overhaul. There's no such thing as being "TOO" safe.
 
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Old 01-18-2018, 06:00 AM
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Originally Posted by Mike189677 View Post
You could do that but you probably still have the same problem. I should have been more specific when I said I thought it was a hyroboost problem. Since both the steering and brakes are affected the power steering pump is the main suspect in my mind as it supplies hydraulic pressure to both the brakes and steering in the hydroboost system. How is the level and condition of the power steering fluid has it ever been changed though we are most likely past that point any leaks anywhere in the system?
Couldn't find any leaks on the steering or brake side. The fluid looks "ok" but I might just try a flush to start with because I don't know when the last time it was changed. The truck is new to me, and has 259k.
 
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Old 01-18-2018, 06:03 AM
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Originally Posted by OneCylinder View Post
How old are your brake pads? If they're worn, that would explain the low pedal. This might be a good time for a brake system overhaul. There's no such thing as being "TOO" safe.
The pads are in pretty good shape. I don't think it would be just the pads that would make the steering lock up as well.

But I agree 100%, cannot be too safe when it comes to brake systems! Especially when these trucks are (mostly) used to haul big loads.
 
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Old 01-18-2018, 02:35 PM
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I had that happen a few years ago and found out the engine must be running for the pump to work. Diesel's use a separate pump since it is a diesel and doesn't have gas engine vacuum. There could be a leak in one of the lines if the engine is running and you still don't have brakes/power steering.
 
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Old 01-18-2018, 08:15 PM
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Ok, I am not an expert on hydro boost, but it’s an assist. The brakes have to work properly without it. You may have to “use both feet” to stop though.

All that said, if the pedal goes to the floor you most likely have air or a bad MC. Was it like this when you got it? If so could be either. If it was fine and just crapped, then the MC. All this assumes you would have noticed a leak.

My drill is to fix the obvious and see whats left. AKA fix the low pedal and then see if there is still a steering problem.
 
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