I've got after-market disc brakes on the front and rear and I have yet to get them to work like I would expect. A little spongy, a lot of pedal travel and I have to use more foot pressure than I would expect for disc. I have bled the brakes multiple times (ensuring the bleeder on the calipers is facing up). No leaks that I'm aware of (pedal does not fade). Pistons / pads are snug on the rotors before applying pedal pressure. I picked up a Chilton's manual the other day and ran across the following statement:
IMPORTANT: On cars with front disc brakes, it will be necessary to hold in the metering valve pin during the bleeding procedure. The metering valve is located beneath the master cylinder and the pin is situated under the rubber boot on the end of the valve housing.
I did not do this when I bled the brakes. What is the significance of the metering valve pin during the bleeding process? Any other ideas on possible issues? Thanks.

 

Did you bleed the master cylinder before you installed it? Do you have a proportioning valve installed?

 

Sorry for the slow response. Out-of-town. The car came with disc on front and rear. The rear brakes were not the right kit for a Camaro so I bought a kit from Right Stuff and installed it. I did not replace the master cylinder. Looking closer at my brake system, the proportioning valve I have is the one that is preset, i.e., has the wire running out of the top to indicate loss of pressure in either the front or back brake lines (I'm not an expert on this so I could be wrong). I think it is preset for drum brakes on the rear so unlikely it is set correctly. I measured the vacuum today and got a reading of 7 during idle and 17 ++ when throttled. I've got a 427 with an agressive roller cam so I suspect the vacuum is on the low side. This is probably why I have to put a little foot into the brakes to get a response. Even so, the stopping power is not near what I would expect for four wheel discs. Thoughts?

I would send a picture but the posting rules indicate i can not post attachments :-(

 

I think you may have more than one issue. The wrong proportioning valve; I'd go with an adjustable. And the possibility of some low vacuum. Since your vacuum should be at peak when you let off the throttle, that's the reading that's most important. Vacuum builds on deceleration, and if it's not there at that point, you may need to go to a hydraulic booster to use power brakes, or go to manual brakes without a power booster.