Thanks for info. I do have a frame mounted master, that's why I need residual valves. The prop valve is mounted higher the master. The truck has stock disc brake front, drum rear. The prop valve is the stock unit and not adjustable. It doesn't work correctly because the truck is much lighter over the rear axle by having just the weight of a bed, instead of all the extra weight of the Suburban body, glass area and seating etc. A lot heavier in factory form. The new prop valve is a Wilwood adjustable type. It should solve the problem of the rear end wanting to come around in a hard stop situation. If any of this doesn't make sense please let me know. Thanks again.