Master cylinder bore size

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440 Mike

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Hello everyone. I'm converting the brakes on a 68 Dart to manual front disc with rear drums. I'd like to use a cast master cylinder with possibly a 15/16" bore. Where can I find this master? Any advice on the choice of bore size welcome.
 
I had the truck 2 bolt with adapter plate, aluminum with 1 1/8" bore on my Duster. It had a hard pedal. Just got my NEW 2 bolt aluminum 15/16" bore from Dr. Diff. 2 days back. $113 with shipping. My Duster with factory discs front and manual brakes had a 4 bolt cast iron unit with 15/16" bore. The cast iron tends to rust inside. The 15/16" bore in aluminum are VERY hard to find. Some say the 1980 D150 basic truck had them. I found no-one able to get them. Called NAPA, Autozone, Oreilly's etc. The Dr. Diff unit is COMPLETELY brand new with reservoir.
 
M/C is bled, and installed. The pedal feel is sooo much better with this new 15/16" unit vs. the 1 1/8" unit I had on the car. I now have a brake pedal feel much better than the previous "standing on a brick" The brake pressure against the pedal gives more of a regulating travel feel.
 
It better not be "too much" of a "regulating feel" because it might still have air in it. Any manual brake should be pretty darn hard. When I converted the 67 to Duster front/ Versailles rear, I just used the factory master. "See if it works" and it did. Rock hard about 1/3 of the way down and stops like nobody's business. If you can look it up, I don't know what the bore is on a 67 Dart drum brake car
 

M/C is bled, and installed. The pedal feel is sooo much better with this new 15/16" unit vs. the 1 1/8" unit I had on the car. I now have a brake pedal feel much better than the previous "standing on a brick" The brake pressure against the pedal gives more of a regulating travel feel.


Good to know. If I understand this right the smaller bore should have more line psi too. How much pedal travel do you have with the 15/16?
 
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