i have a 1994 ford f250. i replaced the master, bench bleed it properly, installed two new front cal.(had to, someone broke both bleeders off) someone also replaced both front steel lines also. no leaks anywhere. i adjusted the rears up fully, checked for leaks in the wheel cyl., then bleed the whole system including the ABS bleeder. i have a great pedal when not running, the minute i start it and hit the pedal, it goes almost all the way to the floor. but truck still stops awesome. i am stuck on this one. only thing it could be is the booster i would think. any advice? anyone ever have this problem? what about the part that screws into the rear line hole on the master? what is this thing? i looks like a valve of some sort. has a plastic piece in it.thanks a lot. mike

 

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thanks a lot. happy to find a place where it is ONLY Ford and Ford ONLY!!!!!!!!

 

Welcome! It sounds like something to do with the booster. Did you make sure the pusher rod is adjusted correctly? This can cause excessive pedal stroke. It goes from the booster into the MC. I would check the vaccuum hose to make sure it is ok. I had a fading brake. It would brake, and then the pedal would travel down until it was like manual brakes. I replaced the booster, and it is fine. It doesn't sound like a bleed problem, but it never hurts to go over it once again. Do you have a brake light? If so, the proportioning valve is out of center. Good luck

 

how do i know if the push rod is adjusted correctly? i know what you are talking about, just do not know how to properly adjust it.vacuum is great, it hold vacuum even if it is not running. i ordered a booster sat. should be in monday. so i will change that. i hate to just keep changing parts. i like to figure out the problem. i keep thinking it is the booster. i bled it so many times. no air at all!!!. no brake light either. do you know what that little valve is the goes between the rear brake line and the MC? could this go bad and cause a air leak? thanks..

 

If you already ordered a new booster, it should come with a template that helps set the dimension. Mine did. Anyway, don't know about the valve.

 

Power temp,, I think I have your answer but I won't know till Get you a tech address. Mean while plug both exits at the MC Then try it. If it remains firm it is not your booster or MC

 

I hope not to get into trouble for this but here goes..
http://www.asashop.org/autoinc/dec99/techtips.htm

 

rich,

i think this is the problem too. i will be jumping it out tomorrow to try it without the unit. thanks for the info

 

I have the EXACT same problem as "powertemp" has....my 94 F-350 has new EVERYTHING except the cailpers and brake booster. NICE hard pedal when engine is off, but when running, pedal sinks almost to floor. Brakes stop well, just annoying to push that far.
I have power bled the system several times, including the RABS valve, and adjusted the rear brakes tight....still sinking pedal when engine running only. I can't see how the brake-booster could be at fault, all that does is give the assist needed to ease the effort of braking....I saw a post stating to actually replace the original master cylinder with one from a F-450 super duty w/o cruise control and that firms up the pedal (?)
ANYONE HAVE AN ANSWER??????
By the way, the rear brake line unit you are asking about coming out of your master cylinder is the REAR brake proportioning valve...engages the rear brakes after the front ones have been engaged about 30%....suprised no one answered that for you.
Hoping to hear from some fellow "brake pedal problem" guys...thanks, Mark

 

The only thing different I have done is I also replaced the rear cyds. I made the ABS
bypass permanent. I don't need something the goverment says I need to help me use my brakes.When I bled the system for the umpteenth time after each part replacement my wife was my helper, Not Runnimg,I had her pump the brakes four times
each time before I turned the bleeder at each wheel. this takes awhile dut I ended up with about half pedal. Make sure you do a final pump-up before starting! I found out that Ford has an issue with the piston size in the MC.that causes our STOPPED pedal fade. Post back please to let me know how it went. Richard

 

Hi guys! Did you solve your pedal fade problems? I have the same problem and would sure like your input. I have bypassed the RABS dump valve,replaced all the brakes and hydraulics,and thats when I noticed the brake pedal goes away when sitting with the engine running.Any good news?
Thanks

 

Nope,

Haven't really found anything new to do. I am only left with the MC, vacuum booster and the RABS valve, but they all test good as much as I can see. I do have a buddy who thinks the vacuum unit is bad...his theory is that the internal boost equilization valve is bad and "making" the pedal sink further then it should....said it happened to him on an old Chrysler....who knows?
I did read somewhere that if you use a MC from a 1992 F-450 superduty w/o cruise then your pedal will be good and hard....has anyone done this? The price is only like $10.00 more then the standard MC. Anyone??

 

The post I put in about bleeding the brakes did work for me. each day I messed with this thing I was finding another bit of air in the system especially the new calipers. The one thing I can stress is to make sure you have the brakes pumped up BEFORE starting. The difference in the master cylinder is this...In 1999 Ford said that the stopped pedal fade could be due to the piston size which creates high pressure with a low volume of fluid and to use the next size larger ie.250 to 350, to reduce pressure and deliver more volume thus putting less stress on the power brakes.
Richard H.

 

try bleeding the brakes backwards, ( this is much easier and do not require help from nobody) you need a hand pump ( $ 5.00 nothing fancy) 3 feet of 1/8 vacumm hose.
this is how i do it: i drain/empty/ the master cylinder reservoir,start from the rear right wheel, connect the hose to the r/r/w bleed fitting and to the hand pump (full of fluid) open bleed fitting 3/4 turn and pump the oil thru the system till the hand pump is half empty , close the bleeder,empty the reservoir again to , refill the hand pump, do the same to all wheels, do not empty the reservoir after the last wheel. start the truck pump the brakes, check reservoir level.
its very simple very fast and very easy once you do it a couple of times.
by the way; this is the proper way to bleed brakes.
regards.