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Leaking flare joint in premade tubing - problem solved - be aware


m-mman
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The car: 1973 Corvette - 350 and Q-jet. Could there be a more stereotypical running gear?

 

The problem: over the years the tractor mechanics have used pliers to remove and install the fuel line at the carb. The flare nut is now chewed up and rounded off. 

 

The solution: Buy a pre-bent tube to run from the fuel pump to the carb from one of the big producers and advertisers. (regular steel, not stainless) 

It arrives and the bends and twists to get it in place are perfect. However IT LEAKS(!)  A "heavy film becoming a drop" type of leak. It is leaking at BOTH the pump and the carb.

Tighten it up with tubing wrenches while holding the receiving part. It still leaks.  Repeat and it still leaks. . . . . 

 

Final solution: Remove the line put it into my own flare tool and perform the final flare making step again. You know, using the clamp with the big cone to squish out the flare.  Reinstall and no more leak. 

 

Don't know what happened. The original double flare looked good, not off center, no burrs. . . was there something maladjusted with their flare tooling?

Dont know, but it took squishing both ends again to get a good seal. 

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 I made SS brake lines for my car. (broke three flair tools)

 They leaked. 

Solution, I cut the stems off of 3/16" pop rivet's and used them as gaskets. Worked fine!    👍

 

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1 hour ago, carbking said:

POSSIBLE - If the line manufacturer also produces stainless lines:

 

Stainless is flared at 37 degrees, everything else at 45 degrees. Maybe the wrong fixture might have been left in the machine.

 

Jon

The stainless repro brake and fuel lines sold by vendors such as Inline Tube and Right Stuff have the same 45 deg flare as do the steel lines they are designed to replace. I've personally made 45 deg double flares on stainless tube for custom brake lines with no issues.

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Joe - in a different lifetime, before some of the companies you mentioned started; we produced fuel lines for a number of multiple carburetor set-ups using original material (aluminum, copper, steel).

 

We had a few requests for stainless lines, so contacted the tubing supplier from where we got our raw tubing.

 

When I asked about stainless, I got shunted to an engineer who asked about my request. When I told him my plans, he asked if I were also reproducing the fittings in the 37 degree flare. When I told him no, he told me that while the stainless can be flared at 45 degrees, it will often crack over time; and they refused to sell me the stainless tubing (liability protection). Again, this was the vendor from whom I normally purchased tubing.

 

This is the source for my comment about the 37 degree for stainless.

 

Because of that comment from an engineer of a company that was turning away a sale from a regular customer, I have never since considered stainless lines.

 

I have no other knowledge on stainless lines.

 

Jon

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6 minutes ago, carbking said:

Joe - in a different lifetime, before some of the companies you mentioned started; we produced fuel lines for a number of multiple carburetor set-ups using original material (aluminum, copper, steel).

 

We had a few requests for stainless lines, so contacted the tubing supplier from where we got our raw tubing.

 

When I asked about stainless, I got shunted to an engineer who asked about my request. When I told him my plans, he asked if I were also reproducing the fittings in the 37 degree flare. When I told him no, he told me that while the stainless can be flared at 45 degrees, it will often crack over time; and they refused to sell me the stainless tubing (liability protection). Again, this was the vendor from whom I normally purchased tubing.

 

This is the source for my comment about the 37 degree for stainless.

 

Because of that comment from an engineer of a company that was turning away a sale from a regular customer, I have never since considered stainless lines.

 

I have no other knowledge on stainless lines.

 

Jon

Typical stainless tubing in MIL-SPEC AN fitting applications use 37 deg single flare, just like aluminum. I've dealt with that in my day job. The mild stainless tubing for aftermarket automotive applications are designed to be direct replacements for the stock steel lines, so they use the same 45 deg double flares and inverted flare nuts. I suspect that the engineer you spoke with was only thinking about the AN fitting single flares.

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5 hours ago, carbking said:

Stainless is flared at 37 degrees, everything else at 45 degrees. Maybe the wrong fixture might have been left in the machine.

This is what I considered after trying to get it tight enough the first time(s).

A good seal only comes from having well matched surfaces, and I could only guess that they were not well matched. 

 

16 hours ago, Gary_Ash said:

Parker makes small cone-shaped copper gaskets to insert in leaky flare joints

I have used these very successfully in my Air conditioning lines. But with a brand new tube I wasn't expect any leakage problems. 

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I just use Cunifer and skip the issues. Of course, might not be concours correct....:D

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On 7/23/2022 at 3:27 PM, HarryLime said:

Neither of those are the inverted flare fittings used on the OP's 1973 Corvette. That is not the problem here.

As I noted above, the aftermarket stainless replacement brake lines use exactly the same 45 deg double flare as do the original steel brake lines. If they didn't, they wouldn't fit.

 

Double-SAE-45-degree-flare.jpg

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