major brake problem

[Double D]

just replaced everything on the brake system except the hard lines -
when its off, it feels like I am getting good pressure in the system. as soon as i turn the motor on, pedal goes all the way to the floor - nothing -
I can not hear any leaks from the booster when the motor is running -
i'm about to google search -
is there something obvious i am missing?
if i cant fix this tonite, the car wont make it to the show tomorrow????

[LMS]

If the pedal is going to the floor you either have a big air pocket in the system, a leak somewhere, or a bad master cylinder.

Check for leaks first.
Then try to bleed it out some more. Just open the valves if you have good flow and let it gravity bleed for 20 min or so adding fluid as needed.
If it still goes to the floor the master cyl is probably bad.

[LMS]

Oh and don't think just because the master cyl is new it can't be bad.

[Double D]

we bled the whole system multiple times -
unhooked the main line and bench bled the master again tonite and ran fluid through to all 4 wheel cyl. until it was clear.
vaccuum to the front end of the booster is working -

why would everything work with the motor off?

[LMS]

Are you sure there are no leaks?

If you are confident the air is all bled out, and cant find a leak go tomorrow and swap out that master cylinder.
Older brake systems are very simple set-ups, has to be one of those 3 things causing the problem.

[LMS]

why would everything work with the motor off?

With the engine off the booster is not helping, it's just your foot doing all the work. When you start the engine you now have that force multiplier helping work the system and it just goes down.

[LMS]

Is it drum brake all around?
If so are they adjusted properly?

[Double D]

drums all around - i thought I had them adjusted pretty close - they were biting pretty good as we were bleeding the lines.
Doubt I'll be able to find a replacement master off the shelf anywhere. just have to start calling first thing in the am I suppose.
Thanks for the tip dave
see you this weekend

[LMS]

Call me in the morning if you need any advice, I am off work.
Will pm my number in case you lost it.

[LMS]

Well, hows it going Steve?

[60Crown]

After mostly driving around last couple days and not checking in here often, I'd like an update as well. LMS covered options thoroughly. My guess is also master. A good friend Nick immediately switches his Cads over to dual master cylinders and I've heard of your scenario before.

[tonytheskin]

ever figure the problem out?