94 F350 7.3 diesel IDI Dualie

It all started with a blown rear line. After changing them, I began having problems with the pedal going to the floor on when pressing hard.

This weekend, I changed:
both rear wheel cylinders
both rear bearing seals
both rear shoes
new hardware
drivers side brake drum
master cylinder
vacuum booster
both front brake hoses
both steel lines going to front brakes
passenger side caliper due to a leaking piston

I did bleed the brakes, bench bled the master cylinder as instructed, and gone through a full quart of brake fluid bleeding the brakes over and over. No air each time. However, the friggin brake pedal will go to the floor ONLY when the motor is running. When the motor is off, I can put both feet on the pedal with my butt off the seat and the pedal will not go to the floor.

Any ideas?

 

if it sits for awhile without running can you easily push the pedal to the floor? sounds like it has a leak and is sucking air where to me..

 

without standing over your operation watchin what youre doin. . .

air in the system is prob the #1 probability. . . .that bein said the other possible problems include: rear brake assembly falling apart or, more likely, theyre out of adjustment. these ole drum brakes lose their ability to "auto-adjust" over time. because you were just in there tearin the brakes up, that increases the likelihood that theyre just not adjusted properly. do you know how to adjust them? thats where i'd start, cuz if theyre adjusted properly and the pedal still goes to the floor then you know there must be air in the system, or theres a leak somewhere. a brake system leak is easy to detect. if, after an "inspection for leaks", you find there are none, that basically narrows it down to air in the system. worst case scenario ya drive it around for a week and that would allow the air pockets to make their way to a place that can be evacuated via the caliper/cylinder brake bleeders. if that still doesnt solve the problem then you can pump brake fluid through the caliper/cylinder bleeders via a syringe or hand pump, which, after completion of all 4 bleeders, would rule out air in the system. end of story.

 

i had one on a 98 f250 that the front hose blew first guy they called put a hose on broke the bleed screw and when i was the only guy that could show up. anyway long of it was you have to bleed through the bleeder because of the design to large of a cavity was the problem hope this helps

 

Before putting the axles back in, I spun the drums until I got the brakes adjusted out where they just started rubbing the drum. I've done many brake jobs on VW's when all they had were manual adjustments. I couldn't even guess how many times I've done brake jobs. It is that this is the first time I have run into this problem.

Two years ago I had replaced the calipers and pads. Still had great brakes. I'm going to call my diesel guy tomorrow and ask him also.

I took the truck out for a spin and it stops better than it has. It will come to a stop from 50 using only about 25% of pedal. Which is better than before. Its just weird that if you push real hard on the pedal (which under normal breaking there is no need to) it goes to the floor. When it does do this, the brakes stay engaged and does not release. I guess it could be that hex my ex-mother-in-law put on me.

 

well this is why i said "without standin over you" . . . .

peoples defenitions of anything via the internet basically results in miscommunication. that bein said, i gave you all the possibilities that you could be seeing (based upon the information that you replaced the master, and assuming the master is in good shape and its not "mysteriously eating brake fluid"). if you see no leaks in the brake system (i.e. meticulously inspect the brake lines/calipers/cylinders[including master]) then that means your problem lies elsewhere. either in adjustment (which you swear to rule out) or air in the system. pumping brake fluid through the bleeder(s) sounds like your next step.

you replaced a lotta stuff in the HYDRAULIC brake system. that bein said, it might take a lotta work to get all the air out. and, as i said earlier, driving it will only help. the longer you drive it, the more the "trapped" air will find its way out of the lines/pistons.

 

Did you bleed the rabs valve? RABS=rear anti-lock brake system, its on the left frame rail there is a bleeder on that critter too!

 

not suggestoin that its a good idea for him at this time, but cant ya just bypass the RABS system? its most likely not workin anyway. . . .

 

You can bypass the rabs but you need run new line to bypass it. Just go ahead and bleed the rabs valve and then the rear brakes