I have a '66 Chevelle that I bought with a disc brake conversion. From what I can tell it's a CPP kit...master cylinder, proportioning valve, calipers, and 2in dropped spindles. Stock drum in the rear.

I have been unhappy with the way it stops...at slow speed, almost stopped, the front wheels grab and lock up.

I turned the rotors and put on new pads...it's a little better, but still grabby.

I thought about an adjustable proportioning valve, but that would adjust the pressure to the rear, not the front, right?

Any ideas?

Could be that the combo valve is not a disc/drum unit and lacks the metering/hold-off component.