Disc Brake Conversion Failing

It is physically impossible for the metering valve to lock one rear brake and not the other. All it does is change the pressure that goes back in the rear brake line. A single line. That feeds BOTH brakes. Think about it.
yes but wouldn't the metering valve also take pressure away from the front? I agree with you that there's a problem in the rear, but I don't think that one problem would impact the front as well. again I'm here for advice, so any and all advice is appreciated.