I replaced the master cylinder along with the power booster and proportioning valve still having problems getting peddle. the peddle goes to the floor and barley stops the car. The system was pressureized to get all fluid moving and free of air. There is a lot of air noise under the dash when i applie the brakes is this a problem. Like i said i replaced the power booster. I have vacume to the booster off the carb. I also replace the wheel cylenders and shoes. Thanks for the help..

 

First, I'm going to guess that your car has cruise control?
The "air noise under the dash" is most likely your cruise control vacuum release valve that is operated by the brake pedal. That's what shuts off cruise when you hit the pedal, and it sounds like you have a vacuum leak. It's probably the valve itself, so for now you can just bypass it.
But that wouldn't be giving you a "dead" brake pedal. Did you have the same problem before you replaced all the brake components? And what do you have, disc/drum, disc/disc, drum/drum? Since you said you replaced the cylinders and shoes, and not "calipers and pads", I'll guess drum brakes...at least on back. If you have disc on the front, have you replaced the calipers?

 

"The system was pressureized to get all fluid moving and free of air. "

What does that mean? You had it power bled? Since power bleeding is not normally done by newbs what did he think was? It kind of sounds like the master cylinder was not bled correctly.

 

Yes the rear are drum the front are disc the master was bench blead and the brake system was pressure blead. the car doesn't have cruise control. im going to check to see if the calipers are working properley. They were working fine before when i checked them but the peddle still went to the floor and i had very little braking power. Ther is a lot of air noise under the dash when i press the brake down. The peddle feels good when the car is off abd goes to the floor very easy when i start the car it doesnt skip down or pulsate it just goes to the floor. it acts like if you were to blow a wheele cylender and had a little front brake left.. Thanks for the response. If anyone has any more ideas please let me no.. thanks again.. no i didnt change the calipers..

 

With pedal fade to the floor the first question is. Are you loosing fluid? I assume the answer is no. Possible issues are

1. Air in the system
2. Brake fluid is passing a seal it is not suppost to. The only place that can happen and not leak to the outside is in the master cylinder. All other seals would cause a lose of brake fluid
3. Something in the system is swelling up every time to press the pedal. This is very rare and should not happen unless someone did some thing they should not have. This was more an issue with older cars the hose parts of the brake lines would swell as they got older. New design hose like your car has will not swell. You may want to check your lines to make sure no one did "brake line repair" with something other then metal. Don't laugh I have seen it.

Calipers that are not leaking or and a vacuum booster failure can not cause the pedal to go to the floor. Both of those could cause a hard brake pedal that does not work well but not a soft pedal.

Good luck.

 

Look under the dash by the brake pedal and see if there is a vacuum module by the mechanism, near the brake light switch. Maybe your car used to have cruise, never know? I've had that happen to me before.
And since the calipers haven't been replaced, try bleeding both again and see if you get any air out of either one. A caliper can be bad even if it doesn't have an external leak. If there is a worn groove on the cylinder of the caliper, it can suck air in on the back-stroke even though it would hold fluid under pressure. If you don't get air when you bleed them, take a vice-grips to each front rubber hose, one at a time. If clamping one down stiffens your pedal, you found the bad caliper.

 

To do a power bleed process right you have to bleed fluid from all four wheels and the combination valve. If that was not done the the power bleeding was useless if fact I would expect it to cause problems. The power bleeder could have forced air into the area that where not bled.

FYI at no time is ther vacuum in a calipur. There is atomsphic pressure and there is high pressure, If there was any type of lower pressure in a calipur the piston would pull away from the pad and that would cause a spongey brake. I guess its possible that air could get in and fluid not get out, but enough to make a pedal go to the floor? That would take years for a leak that was to small to let fluid out. In 7 years of working with 13 other mechanics I never heard of getting air into a brake system that was not there from bad install or repair.

 

do you mean the hose is disconnected or the hose is connected and comming from the carb?

When you replced all those parts, are you sure everything is reconnected?

Have you done a complete bleed with fresh brake fluid yourself, just to kind of double tap the previous work?

 

Gorn, I just went through this exact same brake crap this summer on my 79 Vette. I had a limp pedal, so I bled all 4 and got air out of the right rear caliper. It was good for a couple of pumps of the brake pedal, then it would go limp again. If I pumped the pedal fast and held it down, it would hold and not drop. So I thought I might as well replace the master cyl., but it didn't make any difference. Bled the brakes again, and got air out of the same right rear caliper. Mind you, I was getting NO external fluid leak anywhere. So I decided to replace the caliper, and whattaya know, it fixed the problem straight away. So yeah, my caliper wasn't leaking under pressure, it was letting air IN. And it was doing it in under a minute, not a matter of years!
Another FYI, if you have a warped rotor and a caliper with a wear ridge where the piston seal rests, the fluxuation from the rotor can cause an "air in the caliper" situation. And lucky me, old Vettes are especially good for having caliper issues.

 

Your problem could be a combination of issues. first, air in the braking system. Second, did you adjust the rear shoes. They are suppose to self adjust when backing up and tapping the brake. If this does not work, which is common, you can use a flat head screw driver to adjust the shoe spreader through the back of the dust shield on the bottom.