The system has been bled twice, Rear drum brakes have been adjusted(front has Disk brakes) Boost has been checked (holds pressure), check valve Ok. Push rod adjusted. New master cylinder. No leaks, Clear fluid. I put on the brakes to stop and the peddle goes down slowly to almost totally to the floor. I'm going to double check the new master cylinder tomorrow . Any thoughts on this any suggestions. Thanks everyone.

Air.

Bleeding brakes is almost an art form. You got to figure out how to do it right and not emulsify air into the fluid.

Also have to bench bleed the master cylinder before putting in car.

^^^ This ^^^

The fittings coming out of the MC are NOT at the highest point of the cyl. Meaning, NO MATTER HOW MANY TIMES YOU BLEED IT OR HOW MUCH FLUID YOU RUN THROUGH THERE, the air that is trapped inside the MC will NEVER EVER find its way out. It will remain trapped in there FOREVER. It DOES NOT MATTER how you attempt to bleed it; you can use a vacuum bleeder at the wheels, a pressure bleeder cap, voodoo and chicken blood, DOES NOT MATTER. If you do not "bench bleed" it BEFORE putting it on the car, it will retain air FOREVER.

"Bench bleeding" consists of putting the cyl in a vise such that it's LEVEL, in which case the fitting IS at the highest point; which then allows the air to escape. With the cyl in this state then, you can put it on the car and the normal bleeding procedures will expel any other air.

Please do not argue, do not wheedle or cajole US HERE about how you might think otherwise, do not waste our time or valuable bandwidth. There is no alternative, no bargaining with it, no denial and bull your way through anyway, NOT NOT NOT NOT NOT. You MUST "bench bleed" the MC to cure your ills.

Sounds good.

"Sofakingdom" , Do you think the OP needs to "Bench Bleed" his Master cylinder?

nah, that’s just an wives tale !

mikeceli;

, Do you think the OP needs to "Bench Bleed" his Master cylinder?
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(Turn you computer sound up)

Nah... maybe he does, maybe he doesn't. If he wants to fix his car, he'll take the advice; if he doesn't, but instead wants to try to convince us that he knows more than we do while our cars WORK and his DOESN'T, he'll argue, like the rest of em. Just, if he thinks he know better than those of use who have some BTDT and also UNDERSTAND the thing rather than just "I've always heard" or ""one time I" or "my friend said" or "I think [whatever]" or whatever, he can go his own way and I can't be bothered any further. I'm not inclined to argue with him about it, or listen to (read) him defending his refusal to do the necessary and obvious. I'm tired of that sort of thing on this forum and don't care to be troubled with it anymore.

When I did a complete system, I had stubborn air that would not get out.

As mentioned, if you didn't bench bleed the MC... I bought one of those kits that allows you to tubes into the MC so its easier to get the air moved out. Then I put my plugs in and pumped while it was still in the vice to confirm. Managed to get just a bit more out.

Now, when bleeding the brakes, I used a vacuum bleeder until I had a good flow. Then let it gravity bleed for a bit to let the fluid move a bit slower for a bit. I was also flushing the system.

In the end, it took a few pumps of the 2-man method to get the last bit of firmness I wanted.

Mine is 4-wheel disc, but any brake system must be completely free of Air.

I'm doing a gravity bleed right now, the system has been bled three times, Rear drum brakes have been adjusted(front has Disk brakes) Boost has been checked (holds pressure), check valve Ok. Push rod adjusted. New master cylinder. No leaks, Clear fluid. Bled the MS , Rechecked the master cylinder and checked out the combination valve all good or reset. So I'll know tomorrow. Its been a dandy. Hope this is the time that it works,getting tired of working on brakes. Actually it's been Ok learned a lot.

Well I'm back to the beginning , don't know what else to do. Been interesting but not very productive. People said it can be hard to do, well that is dam sure for me.

What is a gravity bleed? Air goes up, brake fluid goes down. How does that bleed the system?

You just open the zerk's and maybe help it start flowing by pushing down the pedal once, I didn't need to .Then just let it go until it is clear new brake fluid. Some people are big on doing it this way. If it worked I sure would have been

Alright, so you didn't really bleed it that way, you just did that to prime the lines with fluid? And you made sure the fluid reservoir never got low? Because air will get in the master cylinder again if the reservoir ever gets low. And once you actually start air bleeding you never ever want to open a valve without the fluid being under pressure, or else air will go right back in the system.

Honestly, I wouldn't gravity bleed. It's just letting moisture be absorbed into the brake fluid.

I don't have stock lines and had a hell of a time bleeding my brake system. My technique was part of the problem. I've had no issues once I got that sorted out.

Large air bubbles can be purged. Tiny air bubbles can't. Pumping the pedal or moving it too fast will churn large bubbles into tiny bubbles. Once that happens you're screwed and you have to let the car sit for about 20 minutes or more for the bubbles to coalesce into larger bubbles again.

Sink the brake pedal at a slow/moderate speed and don't go all the way to the floor (in other words, always be in movement when the valve is open). Easy, smooth and steady movements. Hold at the bottom for a couple seconds. Then let up at the same slow/moderate rate. Pause at the top. Pausing helps keep tiny air bubbles forming. Repeat maybe 2 - 3 times and top off the master cylinder. NEVER let the fluid level get low or you'll suck air into the master cylinder and you'll be screwed. Don't stab or pump the pedal.

Never open the valve unless the fluid is under pressure (somebody pushing on brake pedal). That means open the valve after your partner pushes on the pedal, and close the valve right before they come to a stop. Don't let the valve be exposed to air. Put a clear plastic tube over the tip of the valve and loop it up so fluid is always on the valve. It will help you monitor air bubbles too.

After the pedal starts to firm up for both front and rear brakes, gently press on the pedal and barely crack the fittings at the master cylinder. You might be surprised how much air comes out. Tighten up again without ever lifting the pedal. This is quick and won't take much.

Bleed the brakes again. I'm totally serious. Your brake pedal should feel fantastic after this.

3rd gen boost pushrods aren't adjustable. How did you do this? And what clearance and how did you take the measurement? If this is off by even a small fraction of an inch then your brake pedal will go really deep before the brakes works.

I made a push rod that was 3/16th longer measured by adjusting to were it just touches the plunger on the master cylinder , then backed up a tiny bit

Why? The stock rod is the correct length.... no?
What gap did you measure at final length setting?

Can't remember exactly, but I think it's supposed to be somewhere around 0.02". Too little and the brake pedal will always have a long throw. Too much and the master cylinder won't properly interact with reservoir.

And what's this "check valve" you speak of? Is that something you added yourself? I could be wrong, but I thought check valves were only needed for ancient cars with master cylinder mounted at a height below the brakes.

The check valve holds pressure in the booster, Worked slightly better with the longer Booster rod and the clearance is still there. The original had to much clearance.

I want a straight answer on the gap measurement.

And why do you think the stock rod became too short? Did you change something?

Ok I ran the booster rod up till it just touched the MC Simply by shortening until it touched the plate.and backed it off a smidgen . A few of hundreds. No clue on why it became to short but it was.

This is the theory of a gravity bleed. Let the fluid move slowly through the system. Since the MC is open, air does not need to move up in the lines. The slow movement should minimize air pockets as the lines are filled. However, it has never worked 100% for me, but has sure helped move the process along. I thought using a vacuum system was the best option. Well, it is for just a flush, but not a fill.

I have found if I have removed a caliper or opened a brake line for some reason, a gravity bleed to get started is best. Good steady drip at each corner. Then pull a good volume with the vacuum system. Let the system sit for a bit, and then finish with a few 2 man system pumps at each corner just to confirm. Has worked like a charm each time since the first time I did it this way.

Next is the fourth bleed , this time a vacuum bleed with a locked combination valve. The second one was also a vac um bleed but I don't know if he locked the combination valve. I'll let you know.

It's hard to know without seeing things firsthand, but the booster pushrod thing sounds suspicious like something is wrong in the parts stack-up of master, booster, pedal assembly. If something is wrong in the stack-up, then the pedal will never feel good.

Ah, I see. I'm a little **** about time the brake fluid is exposed to air so not something I've ever considered. I've heard more than 10 or 15 minutes of exposure to air and you might as well throw away the whole bottle. Not sure if that is an honest good number or just backyard tales.

That seems a bit extreme. To be honest, no matter which method you use I would venture to say the MC is going to be open for that amount of time. Now, I will say I didn't "recycle" the fluid drained back through the system. So, whatever was added to the MC had not been exposed too long.

Horse, meet water.

Water, meet horse.

Anyone care for a drink?