I have a dual later cylinder and all new brake lines with an adjustable proportioning valve in the line to the rear. I have a new combination valve but if I put it in the stock location it interferes with the exhaust manifolds or headers. Is a combination valve even needed in the scenario? Brakes consist of manual disc front and 9x 2 1/2 rear sport wagon brakes. Installing the combination valve up near the master is not an option on this project.
Nope, if your talking about the 71 up combo valve, then no, it is not technically needed, if you have an adjustable valve in the rear, to hold off lockup of the rear brakes until the fronts develop sufficient pressure to stop the car straight. I am assuming you have the earlier splitter valve, that contains the spool valve which seals off the fluid to the front or rear when it is not seeing balanced pressure on each side of it. This turns the light on, and helps you keep a little bit of pedal to stop the car, in case of a major line leak. JW
Paging Devon!.... Was it 1970 that used a separate in-line metering valve? From my understanding the combination valve incorporates a metering/pressure valve which keeps the front disks from applying until the line pressure overcomes the return spring pressure at the rear drums. I don't recall if this was incorporated in the master cylinder in some applications. The proportioning valve limits the max pressure to the rear drums in a panic stop. I don't think it makes a difference during normal or even heavier braking. Another function incorporated in the warning light switch. The Buick chassis manuals have good descriptions of how the systems work.
I currently have the brass body valve on the frame, a 1970 master cylinder and the adjustable valve for rear brakes concealed inside the frame rail.
