master cylinder question - drum/drum to disc/drum???

[Chuck78]

As you may have read elsewhere on here, I am doing my brake upgrades in phases with my 62 that has the combo brake/clutch master cylinder. For now, I am divorcing the clutch and brake cylinders, mounting a new clutch cylinder in the stock linkage location, and adding a power booster with custom brackets that will space it off the firewall far enough to clear a clutch master, and the at the same time, adding a dual circuit brake master. For now, I will stick with a drum/drum master, as swapping the crossmember for discs will take a lot more time than I have at the moment. I was planning on using this drum/drum master:

1967 GMC C35/C3500 PICKUP 5.4L 327cid V8
DORMAN M66787 1-1/8" bore Master Cylinder

I figured at the very least, when I swap to discs, I could get one of these old style power brake disc/drum masters (still has the old deep bore pushrod hole, works with same booster type as I will already have)

1972 GMC C15/C1500 SUBURBAN 5.7L 350cid V8 (E) Master Cylinder
DORMAN Part # M80568 More Info {First Stop #3491500, 3821715, 4089212, 436148C92, 6273936}w/Manual or Power Brakes; Bore = 1-1/8"; Bendix



NOW, what I was wondering, was first off, I think the master that I have on order for drum/drum is going to have residual valves internally like my 62 master does for the brake portion. If not, and a 67 had them inline or in a metering block/prop valve, someone speak up please! I was thinking, that since the bores are going to be the same diameter for drum/drum over to disc/drum, could I just keep this master cylinder and disassemble it and remove one of the two residual check valves internal to the master, and use it as a disc/drum master by just simply adding a disc/drum proportioning valve? Is there something that I don't know that will keep this from working well?


Two other lesser questions, is it the norm for a hydraulic system to still use the same proportions for master cylinder bore vs caliper/wheel cylinder bore diameters, regardless of power or manual brakes????? I figured since my manual brakes and clutch both use a 1-1/8" bore master, that power brakes and same clutch would still both need 1-1/8"

Also, our trucks stock (my 62) has no metering block or proportioning valve. I assume they never came with them, and that I also won't need one when switching to a dual circuit with drum/drum, correct? It would really make sense that in any system, you would want less fluid/power to the rear vs the fronts, but it seems that it's only a real life issue when discussing drum/disc or disc/disc setups. Should I add a proportioning valve when I swap to a dual circuit setup?