brakes dragging

The front brakes wore out prematurely because of dragging. I replaced the rotors and the calipers. A few months later, they're dead again. To be fair, my wife has been delivering pizza out of this van, but it's still premature. Inspection reveals overheated pads once again.

The van has new calipers and properly greased caliper bolts.

What would be the more likely cause of calipers failing to release fully? A faulty master cylinder, or the valve under the car that divides the two sides of the vehicle?

Is it possible to change only the check valve? Or do I have to take the whole cylinder off?

The hard (well, not hard, time consuming) part is bleeding the brakes afterwards, which you'd have to do whether you replaced the check valve or the whole M/C. I don't know what the price of a check valve all by itself is (or even if you can actually buy it all by itself).

Besides, my impression is that you haven't actually diagnosed whether that's the problem yet.

Right.... that's why I was asking for suggestions. I'll check on it tomorrow after work. Thanks for the info.

Don't know if this would apply if it's happening on both sides of the van, but a collapsed brake hose could cause it to drag as well.

Mike