Front Brakes Don't Work - Need Help!

[Yarb]

The check valve is directional. Make sure you have the correct orientation of the valve. Either way you should be able to bleed the brakes properly. Good chance that reaction disc fell out. Ask me how I know..

[Patcon]

If the pedal goes to the floor and the warning light comes on, then only one circuit is building pressure,  regardless of the booster.

So that should leave only a couple of options.

Air in the front circuit: master, lines or calipers

Or

A bad master cylinder

New parts doesn't mean they're good parts...

[Dens240]

I have two new master cylinders and I've tried them both. Still could be bad, but the probability is pretty low. I'm on board with air in the circuit somewhere. I'll keep working it tomorrow but I'm concerned there is some place that is allowing an ingress of air (without leaking fluid?). 

[Captain Obvious]

2 hours ago, Dens240 said:

When I push the brake pedal to the floor, the brake pressure differential warning light comes on. Also, sometimes there is an audible "poof" 

I get a similar "poof" sound when I hit the brakes and they go to the floor. Although it's from me, and not the car...

Sorry, I know it's "too soon", but just couldn't help myself.     

[Zed Head]

3 hours ago, Dens240 said:

When I push the brake pedal to the floor, the brake pressure differential warning light comes on.

Your problem sounds a lot like mine when I had the bleed screws on the bottom.  But yours are on top.  What method are you using for bleeding?  

The MC's can leak internally, the seal for the fronts can blow and the fluid just washes back and forth over the seal as the piston moves.  And quality of aftermarket parts is poor, in general.  Parts from the same manufacturer might have had the same unskilled person building many MCs in a row, repeating the same error.  If you decide to try another MC try a different brand.

I'm going to bet on bleed technique though.

[Dens240]

I have speed bleeders on the calipers and I'm bleeding by opening one, then pumping the brake pedal. In the past, I have also tried vacuum bleeding. I was able to pull fluid though ok but it seemed like I was continuing to pull air - I saw a lot of air bubbles. 

If I had a leak somewhere that was allowing the closed system to not fully pressurize, I assume I'd see evidence of fluid at the leak point. Is there a reason I wouldn't?

[Dens240]

New evidence this morning. Yesterday I laid a shop towel under the pressure warning switch to see if I had anything leaking there. This morning, the towel is wet. Fluid appears to be leaking from the inlet to the switch at the line from the master cylinder. I checked the fitting and it's as tight as it can get. Thinking about removing the line from the MC to the switch and checking the flare at that interface...possibly put it in the flaring tool. We shall see what I find.

 

[Dens240]

Flare looks fine

 

[Dens240]

Even with the good flare, I formed another piece this morning. Homemade on the left, original on the right. 

[Zed Head]

Check the seat in the switch itself.  A bright light and a good look will usually show you the seating/sealing surfaces and if you're getting full contact around the circumference.

Looks like you found your air leak though. Air has much lower viscosity than fluid (of course), you can suck a lot of air in where just a few drops of fluid come out.

[Dens240]

Latest update...I now have pretty solid grip on the right side caliper. Still not getting any grip on the left. The video below will show that when I pump the brakes, I'm not getting real solid fluid flow. I'll start looking for another leak in the left front lines. Nothing obvious so far.

Hopefully you'll be able to zoom in on the video. Again, I'm using speed bleeders.

[Diseazd]

1) Bleed the front master cylinder resevoir again 2) then bleed both front calipers again. If that doesn’t help, remove the master cylinder (you don’t have to remove the lines to push it aside), then pull the plunger and check to see if the reaction disc is in place. 3) if not in place, fish it out and super glue it on to the plunger. Good luck