OK I have some brakes now. Here is what I did.

Disconected the calip but kept it connected to the rubber line and pads removed. I slowly pressed on the pedal till the pistons were out. Then with a hose submerged in a bottle of fresh fluid I manually pressed the pistons back and forth a dozen times switching from piston to piston back and forth back and forth and yes some air was trapped. I did this on both front calip's and put everything back together. then I did the same to the back ones and got more air that was trapped.

Pedal will still go to the floor, but they will lock up.

 

I've got the same issue. 77 up on jack stands for several months after a rear end rebuild. ALL new brakes - new lines, new rubber flex lines, new MC (not rebuilt) and to top it off I rebuilt the calipers. Similar to your situation, the pedal is hard until I fire it up then straight to the floor. It's driving me bonkers (wifes not too happy either as she works the pedal). Going to try to gravity bleed tomorrow. I'll let you know if it works.

Dave

 

Try going here and seeing if any of these could be your problem. http://www.mbmbrakeboosters.com Scroll over to "Tech" and select the drop down for Brake pedal diagnostics - ten reasons for a poor brake pedal. Also look at Booster diagnostics. There is a lot of good brake system information on their website . Maybe something there will help.

 

I said it flat out on the second reply up top in this thread....you want a GOOD pedla that actually stops the car??? toss that damn vacuum booster for a Hydro boost setup....

all else is

Vac boosters do NOT work if at all, for very long....

HB CURES the problems once and forall....

once again....

CASE CLOSED......

 

Not sure if this could be your problem but have you checked the proportioning or combination valve, you may have a blockage there, especially hard to bleed brakes if the switch is closed.

Neil.

 

Hang in there I have a lot you can test.

Step 1 disconnect the 2 lines from the MC and plug them up good. Then start the car and press the brakes. 1 of 2 things will happen... pedal is hard or soft. If the pedal is hard as a rock your MC and booster are in good working order, but if the pedal is soft either one of them is bad or the MC needs to be bleed.

Step 2 put the lines back on and go buy 4 small orange c clamps from Lowes or Home Depot. $10 and place them on all of your rubber lines going to each calip and then close them shut. Do not over tighten them just pretty snug. Now do the same as before, start the car press the pedal and see if the pedal is hard/. If it is good you just narrowed it down to the calip's...maybe one or maybe all have air.

Step 3 one at a time take the c clamps off one calip and see if the pedal is still hard or soft. If hard put it back on and move tot the next pedal and do the same. If it is soft there is air in that calip. Put the c clamp back on and go to the next pedal and again do the same thing.

The goal is to see what pedal's are soft becasue these are the ones that have air in them. You can also do it by breaking down the front and back at different times. Meaning take both c clamps off the front and start the car and press the pedal if soft you know the fronts need bleeding. Then put them back on and take off the backs do the same thing.

I hope this helps. Once you have done this report back and we can go from there.

 

And don't do this.... meaning don't buy crap assuming that it will fix the problem until you understand what the problem is, then fix it.

 

Great suggestions. I'll give it a try this weekend. What did you use to plug up the MC?
:o

 

Just go to AutoZone and go to their brass connector bin an buy a few different ones, but I think they are 1/2 and 9/16. They are less then a buck and it is a good idea to have several sizes on hand all the time, trust me you will use them again.

 

I ended up a couple plugs that fit the MC. With plugs in the pedal was hard with our without the car running. Rules out the booster and MC. My plan is to next move down to the proportioning valve but I don't have the fittings I need. I did try simply clamping the rubber hoses at each wheel. With the car running, the pedal went back to the floor again.

The proportioning valve was the only component not replaced (did rebuild the SS lined calipers). How often does a proportioning valve go bad? If it goes bad, what are the symptom. I do know mine does not leak.

 

Good to hear you pretty much just rulled that out.

How did you block off the rubber lines? Are you sure all 4 were blocked of 100%? If so, that is only telling us one thing...missalligned or bad prop valve. They rarely go bad, but they can be missalligned. There is a way to reallign them, but I am not sure how to do that. I would do a quick search and see what you pull up. However, before you do that keep going with blocking up the prop valve and perform the same test and let us know how you make out.