We seem to have this discussion every couple of years, Bill, and I've
never received a satisfactory answer to what I think is the crucial
question:
Why would anyone *want* to use DOT 3 on anything, British or otherwise?
Is it hard to find LMA where you live? Is the price difference that
great? Is it just natural perversity (as opposed to natural perversion,
which is *my* excuse :-) ?
DOT 3 is inferior to DOT 4 in pretty much every measurable performance
characteristic. Completely aside from the objections I raise
below yet again (:-), what's the benefit?
~ Just thought I'd mention it. I think the historic legend of DOT 3
~ fluids destroying rubber hydraulics is, at least today, somewhat
~ invalid, if not wholly without merit. Anyone have any contemporary
~ horror stories to counter that perception.
Yes. I've lost at least one hydraulic system to DOT 3 and I've helped
rebuild another in which the rubber seals had perished, and we found a
can of DOT 3 in the boot of the car. My perished system was eight or
nine years ago, and the one I helped with was three years ago.
The question is whether the system uses latex or neoprene for its
seals. Latex seals deteriorate in the presence of DOT 3; neoprene
seals don't. Try soaking the seals in a tub of fluid sometime for
an experiment; I've never done that, but I have seen latex gloves
swell and tear in the presence of DOT 3.
If your contention is that any modern reproduction components might
have been made with DOT 3-resistant components, I'd be open to more
information on that. My contention is that the corollary benefits
to DOT 4 outweigh any possible advantage to DOT 3 even if the new
components have been engineered for it, which may or may not be the
case. Even if DOT 3 isn't exactly bad, it's still not as good as DOT 4.
There are many reasons for using DOT 4 in preference to DOT 3, even
in non-British hydraulic systems. Why use DOT 3? Even if it's
cheaper, it sucks up water more rapidly and it doesn't perform as
well under high-stress applications; the boiling point of DOT 3 is
lower than DOT 4 -- that's the primary reason that DOT 4 has a higher
rating than DOT 3.
In short, even if the braking components you have recently purchased
have been made with neoprene instead of latex, there is no benefit to
using DOT 3. Can it be so much cheaper that it's worth the reduced
performance, even without considering the risk of accelerating deterioration
of any original latex seals somewhere in the system?
~ What may have been the perceived problem in the past was, in
~ my opinion, more a case of a failing component (one that was
~ leaking slowly) which lead to the addition of brake fluid
~ (i.e. someone just popped in DOT 3 because the level in the
~ master cylinder had gone down). Given the component failure
~ wasn't going to improve, the ultimate replacement then being required
~ a short time later was probably viewed as being caused by using
~ the DOT 3 instead of the Girling/LMA (DOT 4).
Well, three comments:
1. The DOT 3 does accelerate deterioriation of natural-rubber seals.
It does, it does, it does. :-) Even using DOT 4 fluid won't keep your
seals intact forever, but you may get 20 years out of them instead of
6 months. Yes, that is about the ratio. Really. Been there, had the
pedal go to the floor like that.
2. What is in the past for some people is in the present for others.
I spent part of yesterday putting Naval Jelly on the original master
cylinder of my '63 122S, which uses Lockheed/Girling brakes and as such
requires DOT 4 fluid. Now, it *may* be that some of the newer components
in that car's system use neoprene seals, but I'm not going to take the
chance.
3. The DOT 4 stuff simply works better: it's less hygroscopic, has higher
heat dissipation characteristics, and does more to prevent rust inside
the lines than DOT 3 does. There is no benefit to going to DOT 3 in
any car, but in the case of older British cars that were designed with
latex seals intended for use with DOT 4, there is serious disincentive
to going down to the next lower level of performance.
I cannot urge everyone strongly enough NOT to put DOT 3 fluid into any
British car. There is no benefit, there are a number of detriments listed
above completely aside from the issues of latex deterioration, and the
accelerated deterioration of original-equipment braking seals on older
cars with original seals is documented fact, not hearsay.
The brakes aren't the place to chisel in an attempt to save money. Use
a cheaper wax, or one less application of No-Touch Tire Foam a year, or
something, but for heaven's sake, do the brakes right.
--Scott
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