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?
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.)
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
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
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
Brian Whatcott wrote:
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