Let It Bleed


Can silicone brake fluid go bad? I have a
partial gallon of Dow brand that has gone
golden brown in color and has objects
resembling bread crumbs floating in it. I
bought the full gallon about 20 years ago,
but it has been well sealed since. If this has
gone bad, should I be changing the fluid in
my 1966 Fury I?

Most of what I have, and still use, is also quite
old. I believe the shelf life is longer that any of
us will live—BUT the foreign matter you found
is disconcerting, to say the least. You could
try straining it, but there was a US military
bulletin, dated June, 1977, which read:
“Report of Contaminated Brake Fluid,
Silicone, NSN 9510-01-102-9455, DLA 400-
87-C-5392, All Lots, Dow Corning Corp, all
subject brake fluid manufactured prior to Jan
‘88, all manufacturers, is considered to be
unsatisfactory and should be disposed of.”
Presumably, your Fury has juice from
this same lot. If so, scoop or suction a
sample from a master cylinder reservoir.
Find foreign matter suspended, floating, or
sunken? Change it!
The official Dow Corning spec is 5
years shelf life, but I think that’s extremely
Anyhow, this query got me thinking: Is
there a recommended brake fluid change
interval? Muscle-era FSMs make no mention
whatsoever of changing brake fluid, at all,
ever. Even well into the 2000s, FSMs for
Mopars made no mention at all of brake fluid
drain/refill. Yet, some current Fiat-based
manuals say to swap it every 2 years. Other
car manufacturers specify five years.
What to do? One idea is to check the
moisture (water) content of the fluid, I found
a neat little gizmo on eBay (from seller
97k-cube) that was dirt cheap and produces
believable readings (see photo, right). In the
absence of any diagnostic method, it sure
wouldn’t hurt to drain a pint or so anytime
you are servicing the brakes. You can simply
gravity bleed (open the screws and walk
away, basically), just do not let the master go
dry, or it will have to be bench bled, turning
this into more of a project.
What if you drive your Mopar so seldom
that you haven’t touched the brakes in years?
I think that five-year number is sensible.
This advice applies to any type of brake
fluid, silicone or mineral. In fact, this drain/
refill would be a perfect time to swap to DOT5
silicone, if your car still has non-silicone crap.
If you don’t pump all the DOT3 / 4 stuff out,
that’s perfectly OK, by federal law, all brake
fluids sold in the US must be miscible.

I have been using DOT5 silicone brake fluid
since the later 1970s. I bought a few gallons
of army surplus stuff about 15 years ago,
it still has the purple tint, and no floating
debris. Use of any other brake fluid in our
classic Mopars is sheer folly. Why? Besides
its ability the prevent stuck caliper pistons,
besides the super-high boiling point, beside
the fact that it cannot absorb moisture, #1
is: If spilled on paint, there’s no damage!
Nowadays, Rock Auto had eliminated the
financial pain, so there’s no excuse.
We found this brake fluid moisture tester
on eBay, cheap, from seller 97k-cube. The
green LED indicates no moisture, the other
LEDs are amber and red.

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