First... hello new here and relatively new to the C3 world!

I did do an exhaustive search here and on the web, my buddy and I watched video after video... and we STILL can't get these stupid brakes bled!
It started out with my car pulling hard to the right when doing a sudden hard brake. I suspected the driver's front caliper, but it ended up being the flex line going to the caliper. After replacing the flex line I bled the front and I have what looks like good pressure up front, but still had a soft pedal so I took all 4 tires off and started doing a full bleed. We started in the passenger rear, inner first, then outer and went back and forth between the rear. We tried the 2 person method, but that wasn't working because I could never get more than a 1/4 pedal from the floor (before all this I at least had 3/4 pedal and did have brakes!) We then tried the hand vacuum method and I was able to get some air out but man... there is still no pedal and it seems like the air won't stop coming out! We said screw this and hooked up an electric vacuum pump figuring it would suck any air right out... NOPE.

Neither of us are professional mechanics, but we've both replaced calipers before (on normal cars!) and bled brakes. There are no leaks, I just can't get them bled. Any suggestions?

 

A vacuum pump sucks for vette brakes.
The calipers have lip seals, which are like one way valves.
You will suck air in past the lip seals.

Use a pressure bleeder, or bleed by gravity if time is not a constraint.

 

https://www.summitracing.com/parts/mvp-0105
Power Motive seems to work the best.
What brake fluid are you using?
You may want to do this on a warm day like 80 degrees.
If you were close to me I would loan you mine.
If you don't know the complete car history, you should replace all the hoses and flush, refill and bleed the brake system.

 

I like a vacuum pump myself but had trouble with air seeping past the bleeder screw threads. The trick is to just barely crack open the bleeder.

A Motive Bleeder tank is the way to go, but not everyone has the funds or the ability to make a plate / lid to fit the MC. The MC lid that comes with the tank is just crap. Little chains & hooks? Really? Junk!
If you want to make a lid see my profile, photo album.

Gravity method is pretty much fool-proof and a cheap way to go. You can open all four bleeders in the rear, drain into four water bottles with four clear hoses.
Its a slow process but works. Keep on eye on the MC. Then do the fronts.
Don't touch the pedal until completely done.

 

Whenever you're sucking from the bleeder screws, air will come in from the outside past the threads if you turn them out too much, and it will seem like you can suck air from the caliper forever. Just crack the bleeder a small bit. You may also have to try to seal the bleeder threads.
The 2 man pump/bleed system should work. Slow and easy.
Perhaps you've upset the proportioning/ low presser warning block?

 

Another vote for replacing ALL the flex lines and using the Motive bleeder. I bought one over 10 years ago and have used it many times and on vehicles other than Corvettes

 

I also vote for gravity bleed.
You are sure you still have air coming out because the other cause could be a bad master cylinder.
The 2 man process causes the seals on the master piston to move further down the bore than normal. Any corrosion in the bore in the areas not normally in contact with the seals will damage them.

 

Yes the little j screws are junk, I used a large "C" clamp.

 

You are right the lid and chains are junk. I made a new lid out of 3/4” aluminum and a large C clamp.

 

I'm starting to think something else is bad in the system, or went bad during the bleeding process. Originally I had decent pedal, it just pulled (pretty hard) to the right when I did aggressive braking. I replaced the flex lines and it looks like the brakes in the front are bled and have proper pressure, but I just can't get these back ones to bleed and get a good pedal. We tried gravity bleeding today and it just sat there for well over an hour and nothing... not even a drop of fluid came out. I hate the idea of having it towed to the shop for them to do it, makes me feel defeated and 'it's just brakes'!!!! Neither by buddy or I ever encountered anything like this, and we thought the F150 brakes were being a bit of a pain (but got them bled). We even replaced all the rotors and calipers on his car and had no problem. This thing... best I can get is air and sputters of fluid to come out. There is no way to do the 2 person method because I can't get any pedal to push through from that side- the pedal goes all the way to the floor. Like I said, I at least had brakes before replacing the flex lines, now I have nothing.

 

Check the proportioning/distribution block. If the piston is offset, you could have the problem you're experiencing.

 

Have you double-checked your rear calipers with a dial indicator?

If there's any run-out at all, you can get air to intrude past the caliper piston lip seals. This is classic C2-C3 stuff: As the pistons clamp the pads down, lateral caliper movement (if there is any) will cause the pistons to go in/out quickly and possibly draw air into the caliper. So the person who "thought" the brakes were possibly bled suddenly finds air in the system. Bleed it out well, and it returns. Eventually a person can lose brakes one day. Definitely check all the rotors for run-out and correct as necessary.

If there isn't any run-out then keep bleeding them till they're as good as possible.

 

For the rears some times you need to raise the nose of the car as high as you can. This will help with gravity bleeding. Also start at the right rear at the inboard bleeder.

 

Madmax,
Is your Brake Light Warning Light on? Does it work?

Your pedal to the floor leads me to believe the Prop Valve has been triggered, blocking off the rear brakeline, plus maybe the bulb is burned out or the switch is defective.
If you want to see the innards of one those valves, check out my profile > photo album > brake bleeding.

 

The rear calipers are hard to bleed. I had mine off to bench bleed them. You can turn them on end and bleed them from the top. Another good trick, raise the rear end so the master cylinder it past level from the rear, the rear being higher than the front, then pump the pedal slowly. Any air in the master should come out.

 

Another good trick is to put the nose of the car as high as possible.
Another good trick is to put the rear of the car as high as possible.
Another good trick is to put the car as level as possible.

WTH?

Which process did the factory use while going down the assembly line?

 

Pressure pot.

 

I have two friends that swore gravity was best.
I flushed their systems with a pressure bleeder. Both said their brakes were never that solid.
Take it for what it is worth.
How do you think these cars were built?

 

A level car is just fine as long as the master cylinder is higher than the brake calipers.

 

DUH! It depends what you are doing. If you are bleeding the master cylinder, "raise the back of the car", if you are bleeding the front "raise the front". Bubbles do go to the highest point.