power DRUM brake conversion (with a dual master cylinder)

[jocko]

Thanks Captain, much appreciated. No worries at all - appreciate you posting for others to find this master. Looking at the pic of the back of the mc shows exactly what I would have needed for this to work with a booster. For others - the same view of a manual master cyl would show about a 1.5+" deep hole in the back of that piston.

I would still go with power were it not for the fact that the dual quad manifold would probably preclude it - just doesn't seem to be room for a fitting and the distrib to stuff a fitting in between the two (there is an undrilled boss, but very little room). If for some reason I don't go with that manifold in the future or if, once I get it all together I can find out for sure if there is room, I can still go power and I'm only out the cost of power mc, about $15 (so I'm gonna hang onto your bracket). OReily's did take my booster back, God bless em, even though it'd been many months since I bought it - they seemed to take a "little" sympathy on me for being on crutches when I bought it.

So, going for a quick fix for now - may still go power someday depending on how the build progresses, but at least know what I'm in for and know how to do it now.

This has been a very enlightening weekend!

[Rich 5150 69]

Hey Jocko we`re not done yet.... you can still use the 67 master and split your lines, just in manual mode, it will give a bit more safety.....

[Captainfab]

Once you get the correct master cylinder, you just need to cut he eyelet off of the booster pushrod. Then mount the booster and bracket to the firewall. Temporarily install your original master pushrod on the pedal. Then align the two pushrods, and make a mark on both, where you can cut them both and join them together. This can be done by welding them together, threading and using a coupling nut, or using a sleeve over both and bolting or pinning them together.

On my '66 Suburban, I retained the drum/drum brakes, installed a '72 Impala booster with a power brake '67-'70 master cylinder. This is when I designed my bracket in 1992. That setup has been on there for over 120,000 miles with no problems.

Also, there is absolutely no need for a bellcrank assembly to make this work.

[RUSHNBOBO]

Jocko,
I had some time on my hands so I broke this down for you ...master cylinder 101. Some more semi--useful info, Here you go...................

DRUM/DRUM
Master is designed to deliver fluid pressure and volume to the front and the rear of a braking system in equal proportions. Drum brakes will require less fluid and pressure than disc brakes. Typically a drum brake master will be smaller than a disc master and the fluid reservoir chambers will be equal in size. Since drum brakes require the use of residual pressure valves the original drum master cylinders had residual valves built into the outlets. Later model aftermarket units do not have these valves and they must be installed in the lines externally. Failure to incorporate residual valves will cause spongy brakes.

Generally speaking it's not a good idea to use a drum brake master for disc brakes since the amount of fluid the cylinder pushes will not be sufficient.

DISC/DRUM
A disc / drum master is designed to push more fluid volume to the front disc brakes since disc brakes require more volume than drum brakes. Generally speaking a disc / drum master will have one fluid reservoir larger than the other.This is because the disc brake pads wear faster than the drum shoes and the fluid reservoir will drop faster. Original disc / drum masters had a built in residual pressure valve to the rear drum brakes only.

Never reverse the outlets on a disc / drum master. Doing this will cause the front disc brakes to drag excessively from the residual pressure valve.