I started to remove one of the brake line nuts from the master cylinder with a box wrench and it began to strip on me.

I didn't let it strip much so I went and got some flange nut wrenches and it still started to strip on me.

What can I do to get it out?

Might I have to replace the brake line and the master cylinder?

I'm going to try repeatedly spraying penetrating oil on it and then cleaning it with brake cleaner once it gets moving so I don't contaminate the lines. Is that a good idea? If that method even ends up working at all.

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    Do you have the proper brake line wrench? Applying a little heat from a propane torch can help also. – Moab Aug 26 '16 at 23:35
  • Isn't that the flange nut wrench? – ShaneBird Aug 26 '16 at 23:35
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    Yes, but Cheap wrenches don't work so well, use a high quality brake line wrench. – Moab Aug 26 '16 at 23:37
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    See my answer here.... mechanics.stackexchange.com/a/29475/16882 – Moab Aug 26 '16 at 23:55

For some real difficult line bolt I would suggest you either a plier wrench (http://www.knipex.com/index.php?id=1216&L=1&page=group_detail&parentID=1586&groupID=1500) or as a last-ditch effort use some vice grip pliers (ruining the bolt thereby). Perhaps you want to use some gently applied heat (electric heat-gun)

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    penetrate oil will work when applying heat as it will be sucked into the threads. – Moab Aug 26 '16 at 23:51
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    +1 for the Vice grips. Ive been there before and vice grips got hold of the nut securely and got it loosened without ruining it! (Ruining it any more than already had been) – Steve Oakes Aug 27 '16 at 18:57
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    The bolt is not "fluid tight". It might be a frog butt, but it still will allow penetrating fluid to wick into the threads given enough time, heat, and/or vibration. "The fluid-tightness" comes from either a double flare or ISO bubble flare compression joint. The threads are merely creating the seating/sealing pressure, and are not meant to seal by themselves. – SteveRacer Aug 27 '16 at 20:00
  • I've edited the answer. Thank you all for the correction – Martin Aug 28 '16 at 6:55
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    Vice-grips are my go-to tool for this scenario. The important thing to remember is to tighten them just enough so they bite into the nut a little, but not enough to flatten or distort the line in the process. – barbecue Aug 28 '16 at 14:27

For such scenarios, best is to hammer on nut but parllal to line using blunt piece of metal. I use a cut piece of L-key. This being the most effective. If you use grip plier, probably the line will have to be cut, put a new nut and then get flared the end by some professional.

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