Powerboosting drums

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moparaddiction

moparaddiction

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My 72 swinger has manual drums.... I want to keep drums all around but make them power drums. I have a powerbooster setup off a 76 duster with disc. Question is... which master cylinder do I use? Manual drum cyl. or Power disc cyl.?
 
If you use a non-power MC, you will have to push the pedal harder than with a power MC. That is because the power MC has a smaller bore. That is due to the lever arrangement in the power brackets. Best if you find an MC used for power brakes in drum-drum cars, perhaps a rare combo and only possible pre-1973.

I currently have power brakes on my 10" drum car (65 Dart), with a 7/8"D MC. I would judge the braking as "very assertive". Easy to skid before getting used to it. I put the power MC on just to be ready for later front disks. I don't think you need power for a drum-drum car. Simpler to just get a smaller bore MC for an easier pedal (but more travel).
 
Why would i have to push harder with a non power mc... wouldn't happen it be easier with the power booster?
 
moparaddiction said:
Why would i have to push harder with a non power mc... wouldn't happen it be easier with the power booster?
Click to expand...
If I understand what you wrote, you are thinking it should be easier to push a non-power MC (no) and also(?) easier to push a power MC (yes).

As I stated, the power MC has a smaller bore, which thus means that the non-power MC has a larger bore. A larger bore requires more pedal effort.

People often say, "with a power booster, why would you need an even smaller bore?, sounds backwards". If you don't believe the relative sizes I stated, look it up on rockauto (some PN's specify bore sizes). The power setup is totally different from the manual. In manual brakes, the pedal rod acts directly on the MC piston. In power brakes (A-bodies only), the pedal rod acts on a lever which applies a force to a rod at a longer lever arm that acts on the MC piston. That reduces the force applied (increases motion), so they needed a smaller bore to compensate. Finally, "why the lever deal?". I assume to raise the booster up to clear the valve covers. The alternative was to angle the pedal rod upward, as GM did for their A-body power brakes, which means the MC is angled up too and looks stupid, but that is already true if driving a Camaro.
 
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