Disc Brake Conversion Failing

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.

No. The pressure to the front isn't changed. There's a sliding piston inside the metering block that moves when you bleed the brakes to adjust the pressure to the rear line.

You have to be systematic about this and fix one thing at a time. You know you have a problem at the rear brakes, you have to fix that and then move on to the next one.

I don't know what it is that you did to the rear brakes, but if they both worked before, and only one works now, there's really only a few options. If you didn't adjust the rear brakes, or change any rear brake components, then you probably have something in the line- air, rust, chunk of whatever, etc that's effecting one side. If you did alter or change stuff out on the rear brakes you'll have to get deeper into it.