Generally speaking it's not a good idea to re-use the copper washers from brake lines since the compression causes them to "work-harden" and be less effective the next time they are used.

I'm currently replacing all the original flex lines on my 85' GSL with stainless steel braided and couldn't buy enough copper washers (1 short). Either I'm lazy or impatient, but I'd like to get the car together today.

Would "annealing" the old copper washers work?
Annealing is a process of heating work-hardened metal until it glows and letting it cool slowly, causing the metal to soften.

I'm going to give it a try. If it leaks then I'll get new washers when they're in stock.
Nothing fancy, just holding it over a gas stove.

 

aluminum washers can be reused a few times. my earls plumbing guy threw in some aluminum washers for free when he made the brake lines for repu.

 

I swapped out my oil a while back, the tool room guy told me that same thing about copper washers...

I asked him, "Well why not just tighten it down and then take it off and tighten it again? since the copper gets hard the first time you compress it and soft the second time..." He told me that was a good idea....

<.< I never checked if thats how it acctually works... I doubt it, but I tried that with one of my banjo bolts and I haven't had a leak since.

Maybe it does work?

 

ive reused em and its rare they give trouble. ive heard re annealing does work, but ive never had to do it

 

I reuse the non-crush copper ones all the time. I do lightly sand the ridge of gunk that tends to build up on the edges and make sure all mating surfaces are spotless.

 

Trochoid has a good point - the flatness is probably more critical than the hardness. I always wet sand the washer flat using about 600 grit paper and WD-40 or water. I do the same with copper or aluminum washers.

For annealing, copper is the opposite of steel. Heat it to a dull red, then drop it into cold water. It will soften if you just let it air cool, but quenching is better. This is common knowledge to anyone who has worked with metals - just do a Google search and you will find this info in a hundred places.

 

Yep, I probably should have mentioned how to sand them, that's the important part of the sealing ability. Another point is the surface that the sandpaper is backed with. If you want a piece truely flat after sanding, use wet/dry paper soaked in water or a lube, I like P B Blaster, then stick the paper on a sheet of glass. The sandpaper will stay in place on it's own, then use a finger to sand the wahers in a circular motion.