Had leaks from brake lines from master cylinder and ABS and also 3 front brake lines from the ABS. Replaced them and then replaced master cylinder.
Bench bled master cylinder and then attached to the lines to the ABS. Did normal brake bleed, R rear, L rear, R front, L front. Pedal seemed spongy.
Started truck and put it in gear. WOW NO BRAKES!!! Pedal goes down to the floor. Removed brake lines from the master cylinder and reattached clear plastic hoses to fittings on the master cylinder. Re-bled the master cylinder until only brake fluid shows in the plastic lines - no air.
Have heard that the ABS unit can wind up with air in it. Very possible as had to connect 4 lines to it and they obviously had air in them.
Do not have a scan tool. How can I purge all of the air out of the system? What else could cause the NO BRAKE condition and how can I fix it?
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I had a similar issue. I ended up buying a bi-directional scanner, I believe it was around $100, to specifically bleed to the ABS. I don't believe there's any way around needing a BD scanner to do this, but that's almost definitely the issue.

 

I have the same issue on my 1996 C1500, and I bled and bled the brakes, literally pushing quarts through the lines, using a one man bleeding setup (piece of hose into a jug of brake fluid at each wheel cylinder) and they are better, but still not great. I think you HAVE to have a scan tool that can do the ABS bleed to do this right. I had replaced the master cylinder as well, in fact, everything EXCEPT the vacuum booster.