When I dropped my truck off last night at my mechanics I told him everything that had happened on Saturday. He is checking it out today and I will let you guys know. My thought has been Master Cylinder, as well but......I tend to always buy new vs remanufactured but I do know that even new ones can fail. I do know that I have the vacuum booster and not the hydro one. I guess we will see what today brings.

 

Well, the verdict is in. My excellent mechanic found that the reason that my truck failed to occasionally stop was the vacuum lines going to the brakes were dryrotting and extremely brittle. He said they were not getting much suction at all. I've only owned it a year and a half and I just drove it back to the office and I can tell you that it has NEVER stopped like this before. What a difference this has made. I truly appreciate the comments and concerns. This forum is invaluable.

 

If your brake pedal went to the floor the vacuum lines had NOTHING to do with the problem. You may well have needed them but like I said before the vacuum booster system will cause a loss of pedal assist, if it is weak or not working the pedal will be harder to push, but you will still have brakes, the pedal WILL NOT go to the floor because of it. The hydraulic side of the brake system is the ONLY thing that will allow the pedal to sink to the floor, most likely a defect in the master cylinder.

 

Gotta agree with Jet on this one. The vacuum does not cause your pedal to go to the floor. It only helps you brake. You can easily test this by stomping on your brake pedal with the engine off. Since the engine isn't running, there is no vacuum to assist, but your pedal won't sink to the floor. I would not accept that as a resolution.

 

if I had to guess (based on reading this thread) I would look at the hydroboost system its self, IE belts, pullies, and pump(s) on the 7.3 I know (for what ever reason in Fords wisdom) ran the hydroboost on the same pump as steering) not sure if your truck will have the same or similar, but this is where I would start if my brakes suddenly went to the floor with out warning.


as for emergency stopping, it is possible, have the mash the brake hard, but the best thing to do is IMMEADIATLY get the truck into neutral and apply the ebrake I understand brake failure can be an @$$ puckering situation but the best way to deal with it is get your 8,000LB truck under control and stopped quickly and safely then deal with the aftermath later...

 

jamie read my earlier post, vacuum boost OR hydroboost cannot let the pedal go to the floor, only a problem in the brake hydraulics, the booster only helps push the pedal down.

 

Johnmarian, just out of curiosity, what color is your brake fluid, is it clear, brownish or almost black?