1999 Chevy Camaro I've had braking problems with the rear disc brakes for about five years now. I've replaced the master cylinder, proportioning valve, rear calipers, rear pads, turned the rear rotors, replaced the rear center brake line and performed adjustments with bleeding the system each time. Colorado uses dynamometers for the emission tests which operate under the rear wheels. This is very difficult to test without adequate braking system for the rear wheels. Is there something I'm missing in the process, or has there been a change to fix this issue?
It sounds as if you have replaced everything that could possibly be causing your problem. What you may have to do now is to re-engineer your brake system yourself. Available on the aftermarket is an adjustable proportioning valve. With that, you should be able to increase the pressure to the rear brakes.