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Brake line fitting size ???

 
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QwkTrip
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Joined: 17 Feb 2004
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Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Sun Aug 31, 2014 11:30 pm    Post subject: Brake line fitting size ??? Reply with quote

I think the rear brake line is a very odd size of 6 mm. Can anybody confirm this?

I am also having difficulty determining the specs for the nut. I think it is M12 x 1.0 but not sure.
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aaron_sK
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Joined: 23 Jan 2006
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Location: Back in beautiful Tacompton

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Sep 01, 2014 7:31 am    Post subject: Reply with quote

It's been awhile but as I recall it's the closest metric equivalent of 1/4" (which would indeed be 6mm).

I tossed the stock nuts and put ones with a normal thread on when I reflared the lines.

Are you running the rear into an aftermarket prop valve?
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QwkTrip
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Joined: 17 Feb 2004
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Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Mon Sep 01, 2014 10:11 am    Post subject: Reply with quote

aaron_sK wrote:
Are you running the rear into an aftermarket prop valve?


Yes. And roll stop.

6mm tube is slightly smaller than 1/4" tube. From what I can tell, you can drill out the 6mm nut to work on 1/4" line, but you can't go the other way or it could leak.

I've not been able to find the correct adapter. And unfortunately, most the adapters are too generic in naming convention and just call out M12 x 1.5 bubble flare. Well, that thread is used with both 6mm tube and 1/4" tube and are not interchangeable.
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iansane
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Location: Bothell

1991 Pontiac Trans Am

PostPosted: Mon Sep 01, 2014 11:47 am    Post subject: Reply with quote

QwkTrip wrote:
I've not been able to find the correct adapter. And unfortunately, most the adapters are too generic in naming convention and just call out M12 x 1.5 bubble flare. Well, that thread is used with both 6mm tube and 1/4" tube and are not interchangeable.


This is how I knew I was never going to make it as an engineer. Very Happy When I did the prop valve/line lock install I'm pretty sure I just put standard nuts and re-flared the lines. I'd be willing to bet that the phrase, "Close enough" was uttered a couple of times.

Although I have put at least 100k on the car since then if that is indicative of how 'close enough' can work long term. Smile

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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Mon Sep 01, 2014 12:11 pm    Post subject: Reply with quote

By "standard" nut, you mean 7/16" - 24 double flare?

Last edited by QwkTrip on Mon Sep 01, 2014 6:10 pm; edited 1 time in total
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Twilightoptics
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Location: Auburn , WA

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Sep 01, 2014 12:30 pm    Post subject: Reply with quote

I've always been able to flare the stock line to the next nearest SAE with SAE nut for whatever fitting I'm working with... AKA linelock. Just make a good inverted flare and clean your edges/inside dia after the tubing cutting does it's work.
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Mon Sep 01, 2014 12:49 pm    Post subject: Reply with quote

That's what I was hoping to hear. The American threads seem pretty straight forward with few choices. The metric threads are a bastardized collection of formats.
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aaron_sK
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Joined: 23 Jan 2006
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Location: Back in beautiful Tacompton

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Sep 01, 2014 2:34 pm    Post subject: Reply with quote

Thirding what Paul and Ian have said. I did mine the same way with the 1/4" nut on the GM line. Worked fine.

http://i151.photobucket.com/albums/s131/aaron_sK/85SC/project_1/camaro_project_2177.jpg
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Mon Sep 01, 2014 3:42 pm    Post subject: Reply with quote

I measured everything and made this diagram. This appears to be the hardware I'm starting with stock. All metric bubble flares.
  • All front lines are 3/16" which will take a 3/8"-24 SAE double flare without problem.
  • The rear lines are 6 mm. Seems like there is enough experience here that if I make new flares I can change the ends to 7/16"-24 SAE double flare like what is used with 1/4" (6.35 mm) tubing.


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