Master cylinder discussion

[Hobbit]

I just installed a set of Randy's ss brake lines (Thanks Randy.) and discovered that the master cylinder the PO installed is a 5/8 bore instead of a 11/16. That didn't sound like much until I did the math.
The 5/8 comes out to have a surface area of .312 in.
The 11/16 has .405 in surface area. Therefore the 5/8 only has 77% of the reaction area compared to the 11/16! No wonder the brakes didn't feel right even with the old hoses. Or is my math wrong?

[Pat Kelly]

How do the brakes feel?
I have the parts-n-more master cylinders(s) on my E (with SS lines) and LG (stock hoses).
Both feel normal for the hoses used. The master cylinders are marked ½" on the casting. I've never disassembled to measure so I don't know what size the bore is.

[SG-Olli]

That depends

What do you mean by "the brake did not feel right"?
With the smaller master cylinder you need less force at the lever to get the required force at the brake pads, but it needs more travel to do that. In all the brake should feel a little softer with teh smaller cylinder. With the braided lines the feel should improve anyway.

[Hobbit]

mc

By not feeling right I meant that I had to bring the lever almost to the end of its travel to build up any decent stopping pressure.
I just cleaned up and installed one of the original master cylinders (11/16) that I had and what a difference!
I have never been able to "lock up" the front wheel before, now I can apply all the pressure that I need and still have travel reserve.

[NOMAD]

I went thru the same thing on my '80 Special. The 5/8" bore from the P.O. wouldn't move "enough" fluid. I've installed S/S hose and the correct cylinder and have great brakes with very little travel or finger pressure.

NOMAD