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Unread 09-15-2007, 08:58 AM   #1
glennv
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Brake line fix using compression fittings.

My brake line rusted and was leaking like hell. I went to buy a new line and a union to replace the broken section. The parts store gave me the correct line and a compression fitting to join the new and old sections. The freaking package says do not use on automotive brake systems. WTF. Why would they give this to me?

ANyway, I used it because I need to get the car home. Two questions. Should I replace the fitting with flares and unions and how tight should I have torqued the compression fitting down?

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Unread 09-15-2007, 09:29 AM   #2
ratmonkey
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replace it asap, probably good enough for an emergency "get it home and figure it out later" fix but if you need to stop quick the pressure likely could pop the line.
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Unread 09-15-2007, 09:40 AM   #3
edzakory
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Brake lines use a double flare. You can get the tool as a loaner from AutoZone. You will also need a tubing cutter. Replace asap.
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Unread 12-21-2010, 10:24 AM   #4
tom88xj
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Compression fittings would probably be okay...probably. First off, they have to be made of stronger material than the brake line. That means stainless steel not brass! Then they must be properly installed. That's the area which disqualifies them in most state safety inspections because too many auto mechanics MIGHT not tighten or assemble them correctly. It's not that they are total idiots it's just that they lack the knowledge to analyze mechanical devices. That's best left to those with engineering training.

Compression fitting fail catastrophically because the lines aren't inserted fully or the ferule rings aren't compressed to design specs. This results in insufficient area of the line available to support the applied shear stress and the line extrudes out of the fitting. On the other hand, a flare fitting dumps a tensile load across the entire cross-sectional area of the line. So, using a flare fitting, averts the possibility of sudden separation of the union. Even if it should loosen, it will leak down before total failure giving the operator fair notice via the dashboard warning lights. It's idiot proof...to a degree.

As to accident liability, that would be an issue only if the compression fitting was discovered to be a contributory factor. Having a well-working compression fitting found on a vehicle would not imply liability but would subject the owner to a safety violation.
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Unread 12-21-2010, 10:52 AM   #5
gmiller0737
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Replace it with a flare type union (Metal line will need to be flared with a "Double Flare Tool")
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Unread 12-21-2010, 10:58 AM   #6
bobjp
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I think this is a bad idea, and you should replace the entire brake line. If one part of the line was bad, there is a chance that there are other bad parts.

Also, I would not trust a compression fitting from a parts store; especially one that clearly has no faith in its own product. "Don't use on brakes"????? What other reason than for brake lines would a parts store sell a compression fitting? Maybe for a fuel line? That's just as bad of an idea.

Compression fittings are great in high pressure situations as long as they are quality made and rated for the job. The ones you have don't sound like they are.

Do as others have said by buying a complete brake line and renting the flaring tool.
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Unread 12-21-2010, 11:06 AM   #7
Indy
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x2, it's been a while since I lost control of an angle grinder and had to replace a brake line. But it sure seems like it would a lot easier to swap the line than try and patch it.
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Unread 12-21-2010, 11:16 AM   #8
bradthebard
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The issue is not the strength of the compression fitting. The issue is the line itself. Particularly on a cut line, the brake fluid will cause corrosion over time. The corrosion decreases the commpressive strength and physical diameter of the line. A compression fitting only retains its strength if the line it is on is absulutely stable. Once corrosion causes the line to weaken it will fail. Not if, when.

It will fail after it has been on there long enough for you to think it is working just fine and forget about it.

Change out the whole line.
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Theology is one hundred blind men searching a dark room for a black cat that isn't there.
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Unread 12-21-2010, 11:17 AM   #9
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This question usually opens up a can of worms. Most people say NO to compression fitting on brake lines. I would tend to agree if it a brass fitting, which is what most of the auto parts stores sell. You need to get a steel compression fitting for brake line.

I have used the stainless steel fittings on a few occassions where it was just to difficult to run a new line for one reason or another. Napa or a good auto parts store should carry them. Look for part 7305x3 (Eaton Weatherhead). I know of maintenance guys that use them in factories where the pressure is greater than in a vehicles braking system.
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Unread 12-21-2010, 11:59 AM   #10
DBLJ
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Arnt good compression fittings rated to more pressure then the line?
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Unread 12-21-2010, 12:41 PM   #11
03Jeeper
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I think he has it figured out guys. It's been a few years...
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Unread 12-21-2010, 12:43 PM   #12
bradthebard
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It isn't the fitting that is the problem. It is the eventual corrosion of the line causing the fitting to loosen. The fitting will be perfectly intact as it careens down the road hanging by the side of the brake line that did not corrode further, shrink a bit and then let go while you are descending a hill towards a bus full of orphaned infants and puppies.
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Quote:
Originally Posted by bradthebard View Post
Theology is one hundred blind men searching a dark room for a black cat that isn't there.
Quote:
Originally Posted by schitzangiggles View Post
Atheism is one hundred blind men in a dark room claiming there is no black cat because they can't see it.
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Unread 12-21-2010, 12:43 PM   #13
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Originally Posted by 03Jeeper View Post
I think he has it figured out guys. It's been a few years...
dammit.

I hate when that happens.
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Quote:
Originally Posted by bradthebard View Post
Theology is one hundred blind men searching a dark room for a black cat that isn't there.
Quote:
Originally Posted by schitzangiggles View Post
Atheism is one hundred blind men in a dark room claiming there is no black cat because they can't see it.
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Unread 12-21-2010, 01:30 PM   #14
kg4kzv
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Thats the problem with Compression fittings on brake lines. If it blows off you won't be able to stop for like 4 years unless you run into something first!

Chris
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Unread 12-21-2010, 10:47 PM   #15
tom88xj
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I think he has it figured out guys. It's been a few years...
But there will always be members looking for an answer to this issue. That's what archiving is all about.
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