after replacing my master cylinder (I did bench bleed it) I started bleeding my brakes from rear to front I broke off the bleeder valve on the pass side, at the time my brakes spongey but I had some pedal. So I ended up replacing the pass side caliper and continued bleeding but now I'm getting a constant hissing sound after I the pedal is pushed in, it doesnt go all the way to the floor but makes this noise, any ideas?

 

Year, make, model, power or manual brakes, with or without ABS? Why was master cylinder replaced?

 

98 blazer 4WD, power brakes, I dont think it has ABS (new vehicle to me and I dont know to much about chevys) I replaced the master cyclinder because I kept losing brake pedal slowly until I didnt have any even after bleeding so I figured I needed a new one

 

yes I do have ABS

 

When you replace the Master cylinder on an aBS truck, you have to bleed the ABS actuator. Usually job for advanced scan tool. Search to find other options.

But that hiss comes from the Power Brake booster. Was there adjustment screw on the master cylinder pin? If so, must be set at exactly the right height for the application