brake pedal slowly to the floor - Ford Powerstroke Diesel Forum
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post #1 of 40 Old 07-29-2009, 05:15 PM Thread Starter
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brake pedal slowly to the floor

I am working on the brakes on a 1994 F-250. Not my truck so I don't know when this problem started. There are no fluid leaks, front or back, on this truck. When you mash the pedal the first time, it goes over halfway down. While holding steady pressure on the pedal, it will go almost all the way to the floor. If you pump the pedal 3 or 4 times, the pedal returns to the top but steady pressure will take it almost all the way to the floor. I first checked the adjustment on the rear brakes and adjusted them till they locked down and then backed off until adjusted correctly. Still the same with the pedal. I then decided that the fluid must be by-passing in the master cylinder so I changed it and bled the system. Still the same with the pedal. I the changed the brake valve on the frame, bled the brakes, same with the pedal. I could hear a small air leak when I mashed the brakes and since this was the last thing I thought it could be, I changed the brake booster also. STILL, pedal slowly goes to the floor. This problem has stumped me! It doesn't seem to be air because it doesn't feel spongy, as the pedal will slowly continue to the floor. Any help will keep me from going postal on this truck. Thanks!

Last edited by forrestgump; 07-29-2009 at 05:21 PM.
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post #2 of 40 Old 07-29-2009, 05:23 PM
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Originally Posted by forrestgump View Post
I am working on the brakes on a 1994 F-250. Not my truck so I don't know when this problem started. There are no fluid leaks, front or back, on this truck. When you mash the pedal the first time, it goes over halfway down. While holding steady pressure on the pedal, it will go almost all the way to the floor. If you pump the pedal 3 or 4 times, the pedal returns to the top but steady pressure will take it almost all the way to the floor. I first checked the adjustment on the rear brakes and adjusted them till they locked down and then backed off until adjusted correctly. Still the same with the pedal. I then decided that the fluid must be by-passing in the master cylinder so I changed it and bled the system. Still the same with the pedal. I the changed the brake valve on the frame, bled the brakes, same with the pedal. I could hear a small air leak when I mashed the brakes and since this was the last thing I thought it could be, I changed the brake booster also. STILL, pedal slowly goes to the floor. This problem has stumped me! It doesn't seem to be air because it doesn't feel spongy, as the pedal will slowly continue to the floor. Any help will keep me from going postal on this truck. Thanks!
My 95 did the same thing and I had to replace the brake booster. Fixed the problem.

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post #3 of 40 Old 07-29-2009, 05:26 PM
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my ex was similar, i unplugged the abs. it was rear abs, I unhooked it from the rear differential
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post #4 of 40 Old 07-29-2009, 05:31 PM
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mine does the same thing idk what it is either but it stops just fine

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post #5 of 40 Old 07-29-2009, 05:32 PM
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my ex was similar, i unplugged the abs. it was rear abs, I unhooked it from the rear differential
Totally different setup. Your Ex had hydroboost brakes and not vacuum brakes. I'm surprised your Ex didn't shift wierd after you unplugged the rear speed sensor.

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post #6 of 40 Old 07-29-2009, 05:33 PM Thread Starter
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Originally Posted by dhanna6powerstroke View Post
My 95 did the same thing and I had to replace the brake booster. Fixed the problem.
If only that would have fixed this one. I'm thinking about taking the master cylinder back to the parts store and getting another just to make sure that it is not by-passing internally also!
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post #7 of 40 Old 07-29-2009, 05:33 PM
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no shifted fine, I replaced the master on the ex. brakes would go to floor with constant pressure too. I could not find it. bled em a bunch of times.
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post #8 of 40 Old 07-29-2009, 05:36 PM
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Originally Posted by forrestgump View Post
If only that would have fixed this one. I'm thinking about taking the master cylinder back to the parts store and getting another just to make sure that it is not by-passing internally also!
You didn't say anything in your post about replacing the vacuum booster. You said you replaced the master cylinder and the valve on the frame. Your small air leak/hissing noise is coming from the booster which is what the master cylinder bolts to. The diaphram inside is bad.

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post #9 of 40 Old 07-29-2009, 05:38 PM Thread Starter
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Originally Posted by jethro View Post
mine does the same thing idk what it is either but it stops just fine
This one does also, but the guy who owns the truck wants to fix it. I also would like to know what it would take to fix it since it has kicked my butt!
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post #10 of 40 Old 07-29-2009, 05:39 PM
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sounds like a master, id take it back and get another one, make sure you bench bleed the new master. if you didnt bench bleed the new master that could have destroyed it.

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