Opening up wheels/brakes/axles for projects, could use some parts selection help

[eightynine4x4]

So I’ve got to fix this small leak at one of the brake line fittings in rear. I had not touched it and only discovered it while doing the rear stuff.
It leaks along the line juncture itself, not around the threads.
I’ve tried tightening it with no success, but did successfully get it slightly undone. So it’s leaking a little faster although still very slowly.
Does this leaking along actual line mean something different than if it was leaking just along the threads? Maybe that the line tip/end will have an issue still even if I replace the fitting?
Also what size is the fitting? I’d like to have new one on hand before opening this up.

 

[lowspeedpursuit]

The nominal fitting size should be 3/8". You really want a brake line wrench to make sure it's tight without deforming. If it's fully tight and it's still leaking, you need to redo the end of the line. Even if it was a problem with the fitting, brake line fittings go on before the line is flared; replacing the fitting necessarily means reflaring the line as well.

That line looks like it's already cunifer, which is pretty easy to work with. If there's any slack at all, you can cut the old flare off the line, slide on a new fitting, and reflare. If there's literally zero slack, you'll need to bend up a new line.

 

[Uncle Gump]

First question... is that copper line?

The line is 3/16th... so you need a 3/16 line nut... which uses a 3/8 wrench. That should also be a double flare on the line.

Single flares and copper line should never be used in a brake system.

 

[lowspeedpursuit]

...copper line should never be used in a brake system.

This sounds important, so I want to clariy: are you saying that pure copper specifically is inappropriate for brake lines, or cunifer? I've never seen copper brake line, but I see a ton of cunifer (nicopp / cupro-nickel alloy). If that stuff is actually dangerous, that's fairly big news to me.

 

[Uncle Gump]

I've never used NiCop... but I'm going to try it next time I redo brake lines.

I was talking straight copper tube. I've never heard of it called cunifer.

 

[lowspeedpursuit]

Cunifer (and I guess NiCopp) might be brand names specific companies use for cupronickel. I've rarely worked with anything else, honestly. If you live somewhere rusty, steel is worthless, and stainless can be difficult, so if nobody offers prebent hardline kits for your application, I thought it was the best choice. I first heard about cupronickel working on my Wrangler's 8.8 swap in 2019, and I haven't had any leaks or deformation since.