Fluid leak from lines at brake master cylinder
 

Replaced master cylinder. Had a friend step on the pedal. A tiny bit of fluid is leaking past the threads. Tightened them as far as I dare and theres still some seeping when he holds the pedal down. Anyone recommend anything I can put on the threads to seal it? I've heard teflon tape is bad for this kind of thing, so I didn't try, but has anyone actually tried it?

I did a search but didn't really find anything on this. Gotta get this thing driving by sunset, so any help is appreciated.

EDIT: Tightened it to about 9999.5 ft/lbs and leak stopped. Fail. Literally put all my weight on the wrench. Surprised it didn't break.

So those were the original flare fittings you were cranking down on? Those are steel, yes? I can tell you from experience that if you do that with brass, the fitting will split or shear off. I did that with one of the FM fittings that came with my prop valve. It was leaking so I just cranked it down trying to get it to seal, until it snapped.

The replacement got some thread sealer. I used white teflon paste. Wilwood supplies their brass fittings pre-coated with some sort of red thread locker, not sure if it's exactly identical to red Loctite or not. Anyway, the teflon paste worked fine for me. I installed the prop valve about 8-9 months ago, done 5 track days in that time and have had zero leaks, and I do watch it like a hawk for any evidence of fluid seeping past the threads.

Yep, original ones. I really did not expect to have to tighten them so damn much. Any other bolt that size would have easily snapped/stripped.

Brave one leaning on the wrench. A flare fitting should never need to be tightened like that and frankly, in my opinion should not be, if everything is correct. Either the flare or the nut is boogered. I don't like using sealants on stuff like that, that should not require it. That would be a bandaid.

Oh trust me, I was fucking terrified. Didn't really have a choice though. Drove to get some food and no leaks. Gonna check again tomorrow.

Only fix I would trust now after having muscled it that hard, would be to rent a flare tool, get a new flare nut, and cut the existing flare off and redo it, bend tubing as needed to make it work. But I'm ---- like that.

Sigh. I'm assuming Mazda doesn't sell that specific line? If there are no leaks I may just leave it alone.

Not saying there aren't other ways, but for me, I would only trust a redo. Let others chime in, I'm for sure not a brake master.

^This... the ONLY way to fix a leaking flare is to redo it. Thread sealants are simply masking the symptom, because when properly done they do no sealing. Most times if the flare won't reseal it's one of two reasons, either you buggered up the sealing surface getting it apart or you got some grit into the seating area.

Be meticulous about dirt not getting into things (and don't trust the guys who built the master cylinder that it's clean), and be careful taking things apart and you won't have an issue 99% of the time.

Well...not leaking anymore. :giggle:

Seriously though, if its leaking again when I go check again in a couple hours, I guess I'm redoing it. :facepalm:

You absolutely sure it isn't cross threaded? You should be able to get a leak free seal on a flare with little more than snug.

If it was cross threaded wouldn't it have stripped? Still threads and unthreads just fine.

If you think that part is fine, I suggest checking the flare. Probably split. Cut it off, and re-flare as suggested above. If in doubt, buy another line. Brakes are one place you can't tolerate anything less than right.

The master came with a bag of plastic threaded plugs, for bench bleeding. I don't know how I didn't notice it before, but the plug doesn't go in straight to the threaded hole in question. It looks like the threads in the hole aren't straight. The flare nut LOOKS crossthreaded, but really isn't.
Fuuuuuuuuuuuuuuuuuuuuuuuu :facepalm:

No leaks though.