Question about brake line size when upgrading master cylinder

I replaced the single chamber M/C in my '41 Buick with a dual chamber unit. The original brake lines were large...looks like 1/4" ID (5/16" OD).

First...and this may be a dumb question...does brake line size refer to inner or outer diameter? I thought they were OD, but it surprised me that the lines were larger than 1/4" if that was the case.

That being said, can I go to a standard 1/4" line with my new master cylinder?
Thanks for the input.
Curt

 

IMO 3/16" works just fine, and is easy to install.

I would like to hear others opinions on line size though. I just don't see the advantage of a bigger line... someone tell me if and why I am wrong?

 

3/16" Plenty of flow, no pressure expansion/flex issues.

 

Tubing (brake/fuel line) size is OD, pipe is ID.
Yes, you can use 1/4" line, but 3/16" is really all you need, and much easier to work with.

 

Tubing is sized by ID. Yours seems awfully large for a stock application. Perhaps it has be replumbed.


As for the question about using the larger (older) lines with the new M/C.....I 'think' it shouldn't matter. The way I reasoned it is this: Theoretically the lines are full of fluid. Likewise, the wheel cylinders (and/or caliper chambers), so.....the volume of fluid that moves is that which is required to move the brake pistons and is provided by the M/C. Seems to me the line size is irrelevant.

However, that said, I had an experience with a '47 Ford a few years ago that caused me t wonder. The first setup I used was stock rear brakes with new parts including the wheel cylinders and and all new steel & flexible lines. On the front I installed a Speedway big disc brake kit. The M/C was a '67 to '72 Mustang unit. The lines to the fronts were 3/16". I installed 10# rear and 2# residual pressure valves. Try as I might, bled, and bled again, I always had a "soft" pedal. I am not a novice at this.

A few months later, I chose to change the rear axle to open drive. Installed an 8" Ford with, again, all new brakes parts. However, since all the parts being used were originally fed with 3/16" line, that is what I installed. Bled the brakes carefully and, voila', a full pedal. so what made the difference? I felt convinced the original setup was properly bled and had no air in the system. It still doesn't make sense to me that line size should have had any effect.

Ray

 

3/16" is fine, and like most people said, it's easier on the hands and tools when bending to fit.

 

The bigger the piping the more effect you'll notice of the lines flexing under load, and the restriction to the displaced fluid being less noticeable will also give you a softer response. A viscous fluid being pushed through a narrower pipe will give a harder feel as it's harder to make it shift.

Other than that, it's the volume displaced that is relevant, and being a fluid under pressure it will flow easily through any size of pipe you choose to use, so smaller is not a hindrance.

Go for the 3/16" piping, as stated, no need for bigger.

Cheers, Eddie

 

Most old GM cars had 1/4 and some had both 1/4 and 3/16. Use as is are change it to 3/16.