> ... I have been plagued by numerous brake line leaks...
A leak-free joint is formed when the inner surface of the flare is
firmly and uniformly pressed against a half-round fitting inside
the mating component.
Take a light and look inside the brake line fitting on a rear
cylinder, the master cylinder, the clutch master or slave, or a
distribution block (note: some of the front caliper fittings are ISO,
not double flare, and I'm not referring to those here). You'll see a
half-round surface with a hole (to pass the fluid) in the center. The
flare fits around this surface, and the nut then presses against the
back of the flare, forcing the surfaces into a leak-free union.
Now, there actually is a reason for this long-winded description.
If the pipe twists or turns at all when the nut was being tightened or
loosened, then the end of the pipe is scraped across the surface
of that half-round mating joint. With the pressure involved, it is
likely that the half-round fitting will be permanently galled - an
uneven, rounded groove is sliced into its surface (same thing can
happen if godzilla tightens the fitting.)
Look closely at a used component. Most likely, you will be able to
see where the flare mated - hopefully just a slight blemish, but
if the joint was ever abused (overtightened, twisted, misaligned, bad
pipe flare) you'll see galling - sometimes pretty severe.
If the surface is galled, the pipe is never going to be able to achieve
a smooth, complete seal. Crunching down hard on the nut may manage
to crush the tube into the surface; the resultant deformation of the flare
and/or the mating surface may be enough to prevent leakage, but at
the cost of further damage and and an even harder task of getting a tight
seal 'the next time'.
I suspect that the half-round fitting can be obtained from 'somewhere'
and installed 'somehow' (certainly shops that resleeve and properly
rebuild brake components have some way of refurbishing these
assemblies). I'm not privy to where to get the pieces, though, and I
don't have the machine equipment to try making my own.
So I've dealt with this issue in two ways (besides buying new parts).
But if you ask, I'll deny I've ever tried these techniques :-)
First, for minor galling, I've taken a piece of hardwood dowel and
'cupped' the end so it's concave and approximately matches the curve
of the fitting (cut a piece a couple of inches long, chuck it in a drill,
and then use sandpaper, file, etc to carefully shape the spinning end).
Then, I goop valve grinding compound into the cup and use it (with the
drill providing the power) to grind and smooth the fitting. Go slow,
check frequently (you don't want to make things worse), and be sure
to clean the part thoroughly when done!! Thoroughly!! Every speck!!
In a pinch, on a badly galled fitting, I used a copper washer of the
right size (just small enough to fit into the fitting). I pre-formed it
into a semi-round shape, and clamped it between the flare and the
bad fitting. As the copper crushed down, it took on the shape of the
damage and sealed the joint. The next owner will scratch his head
if he pulls the joint apart and finds a crushed, deformed washer in
there, I'm sure :-)
-- John
John F Sandhoff sandhoff@csus.edu Sacramento, CA
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