My brake pedal slowly goes to the floor with the motor running. With the motor turned off, the pedal stays hard. I used both feet to press the brake pedal for 20 seconds...it will hold it`s position. There is no fluid loss from the reservoir, or any visable leaks from the master cylinder. I would appreciate some advise.

 

Possibly internal leakage in the master cylinder.

 

Wouldn`t it also leak with the engine NOT running?

 

ford had this issue in some of thier trucks in years past. i remember putting 3 NEW masters on the same van in the same day.....after some research found a tsb that said this problem was "normal". we released the van and never had another master cyl problem out of it. if youre not having any braking issues with it i wud run it. just keep an eye on it for a while

 

I`m having a major issue with this problem! I have very little stopping power. If I have to make a panic stop..........I CAN`T. I have only 3-4 seconds to bring the vehicle to a stop, before the pedal hits the floor.

 

DO NOT Drive the truck until you fix the problem, total brake loss is possible. To me it also sounds like a master cylinder issue.

 

First things first. check that your rear brakes are adj propperly, if they aren't this will make the pedal sink to the floor. Once that has been checked and is good then go ahead and replace the master

 

The brakes are all NEW. There are no visible leaks. I bleed the lines twice. The pedal is hard with the engine turned OFF. The only logical answer is the Brake Booster. Of course, logic doesn`t mean much when it comes to many truck pronlems. I would like to get a definative answer before I start buying parts. I did a "search" on the forums, but could not find a brake problem with the same symptoms as mine.

 

Is it possible you can't push the pedal down enough without assist to get to the "bad" spot in the master? This was happening to my dad's E150 van, stopped ok under normal braking, but would sink to the floor when "panic" stops were required it would slowly go to the floor. Pedal was fine with truck off. Just a thought. Good idea to pull drums and check everything one more time as well, easy to do.

 

OK now in your first post you did not tell us you just did a brake job on it. Was it doing this BEFORE you put all new brakes on it?

 

If your pedal is going to the floor, the fluid HAS to be going somewhere. It either is leaking from a wheel cylinder, or brake line, or there is internal leakage in the master allowing fluid back past the piston seals as it travels forward and allowing further pedal travel. If you have no visible fluid loss at all four wheels and your master cylinder fluid level does not change, then my bet is internal leakage in the master. Had the same problem on mine.

 

Thanks for all the imput. First to Larry...I did not notice any problem before the brake-job, but I never had to make a panic stop before I had it done. So, the problem could have existed without me realizing that I had a problem. "gorms" posted; His dad`s E150 had the same problem. He advised to pull the drums. What would I check for?...leaks, any thing else?....To "contractor" There is no visible leakage anywhere, and the fluid level in the master cylinder has not changed in the 2200 mile trip I just took with my very heavy "slide-in camper". The rear brakes were adjusted after the brake job. I also had larger wheel cylinders installed due to the fact the bleeders broke off on the old ones. So.......where do I go from here??

 

When I do my brakes the pedal will go all the way to the floor until I get ALL the air out of the system. I sometimes have to bleed them 3 times before all the air is gone, especially if I am doing cylinders or replacing any lines. Either you have air in the system still or the master is bad.

 

It's very common for internal MC leaks to show up after brake work when the pedal is pushed all the way to the floor during bleeding.
The cylinder is often rusty in the area where it normally doesn't travel in normal braking.
Pushing the pedal to the floor tears up the MC seals.
I usually vacuum bleed to avoid this but if you must pump the pedal to bleed it's a good idea to put a block under the pedal to limit the travel to what it is during normal braking.

 

I had a nightmare of a brake problem like this ,but my ABS and BRAKE lights were on. Turned out the hydroboost for the power steering and master cylinder were leaking between each other there was a seal between them that was broken. They kind of work off each other, I figured that out why my power steering wouldnt work with my brakes all the way to the floor one day even before this problem happened
I replaced Master cylinder and hydroboost . worked fine