My 61 Olds 98 has original 3/16 brake lines, I used a caliper to measure. There is a long, rusty run, along the frame, going to the rear, which splits in two, going to either brake cylinder.
My question is, do I splice in a new chunk of 3/16 wherever needed, or do I replace the entire run? Do I keep 3/16 or increase to 1/4?

Thanks for the input friends,

 

My $.02 - Replace it all at once, using the same size(s).

 

The diameter of the line doesn't matter. Brake systems don't flow a lot of fluid once the air is bled out. Is there a reason why you think the engineers who originally specified 3/16" were wrong? And yes, replace the whole line.

 

I didn’t know for sure about the diameter. Keep it as is I will do.
Thanks for the feedback Joe.