Automotive Brake Line Repair

I've encountered several splice repairs made with a Dorman brand compression fitting on automotive steel brake line. I was trained this was not an acceptable or legal method of repair. I've found the DOT regulation regarding splicing of tubing which states all fittings must meet SAE Standard J512. This I can not find. Anyone familiar with the SAE Standard and whether it allows for the use of compression fittings as opposed to double flared fittings?

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Whoever gave you the advice about compression fittings in vehicle brake lines apparently had some experience in the field .

1) Given the vibrations and corrosion environment of motor vehicles, which tends to degrade connections by temperature and pressure (long runs stress tubes as temperature and line pressure changes, and the compression connection will then "slip and chafe"), adjunct contamination (corrosion from contamination gathered at the edges which eat into the tube at the seal point), and vibration (compression interface being moved about, and if it is an anti-node, moved a lot), and 2) the need for brake fluid to be kept sealed from moisture so as to protect the brake parts from moisture, and 3) my experience and the reliability of various hydraulic fitting types from experience in the (vibration) testing equipment company, and 4) the differences in the assembler's technical ability to achieve a perfect seal using flares vs compression fittings

I would never use a compression fitting on a vehicle brake line other than supported at the rigid manifold, even if J512 allowed it - or for that matter, not on my brake line proper even if it REQUIRED it (in the latter case, I'd be having a long chat with the J512 committee)

While compression fittings are slightly less difficult to make than flared, and for short-term indoor use they are often satisfactory if the connection is secured, imho for long term reliability in ugly environments, flared (45 and 37) have it hands down.

(I am sure there are others that may have a somewhat different opinion.)


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SAE J512 details mostly flare and inverted flare fittings in the 1983 handbooks that I have on hand. However the standard does include seat inserts for reverse flare fittings in table 7A in tube diameters

1/8 in to 3/4 in. Surprisingly, I notice a diagram of a tapered sleeve as figure 15 next page, of the type I associate with regular compression fittings. However the next standard (in this handbook) is SAE J246, Spherical and flanged sleeve (compression) tube fittings.

Not sure how the Dorman fitting is configured, however. Hope this helps a little

Brian Whatcott Altus OK

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Brian Whatcott

Thanks for the reply. I'm an automotive technician with a customer who presented a vehicle having a series of brake line splices using a Dorman /Motormite brand of what appears to be a common compression fitting . . . ferrells, coupler and two nuts. I advised my customer I do not install this type of fitting as I was trained these were both unsafe and illegal. My customer ask what law it violated which I am now trying to ferret out. I have seen seat inserts on 37* aluminum fittings used in off road racing applications not on DOT applications. It would seem the 'reverse flare' language used in conjunction with the seat insert standard might preclude this from being a 'compression type fitting.

Brian Whatcott wrote:

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