57 Brake line to wheel cyl

[60eldo]

 Is it a good idea to put a copper washer between the new brake line, rubber, and the wheel cyl. Some say yes, some say not needed. Thoughts please

[m-mman]

If you are referring to the spot where the flexible (rubber) brake hose screws into the front wheel cylinder at the backing plate then YES!  The little copper washer is an integral part of the sealing mechanism for that thread type.

And its not just A copper washer, it is THE correct copper washer. it is properly sized and has little concentric rings stamped into it to aid in the sealing. I have suspected that they might have some soft 'crush' aspect to their design but I have not been able to confirm it. BUT it is certainly not just any old 'copper' washer.

I dont understand why anyone would suggest otherwise?

Sealing against fluid leaks on automobiles is quite a science.
Understanding HOW sealing systems work; knowing which direction a rubber seal should be installed (which way the lip faces) and the differences between straight threads and tapered threads as well as appreciating the mechanics of how a tubing flair seals is something that ANYONE who works on a car should review and understand thoroughly.