Date: Thu, 19 Aug 2010 21:13:26 -0500
Reply-To: mcneely4@COX.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dave Mcneely <mcneely4@COX.NET>
Subject: Re: brake question
In-Reply-To: <AANLkTik1Se15SaBgxL5oWdgvHAPA95iHGfQy12ompJkP@mail.gmail.com>
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---- Michael Snow <slowmachine82@gmail.com> wrote:
> On Thu, Aug 19, 2010 at 8:29 PM, <mcneely4@cox.net> wrote:
> > Michael, what do you want me to document -- that there are differences in chemistry?
>
> I want to make it clear that DOT 4 brake fluids are backwards
> compatible with DOT 3 systems. Regardless of whether a brake system
> is filled with DOT 3 or DOT 4 brake fluid, DOT 4 fluid is safe and
> advisable for top-up, refill, flush/fill, etc. The fundamental
> difference is in the boiling point, not the basic chemistry.
Well, you may have done that. I am not sure what "basic chemistry" means. I once taught a course called that, for liberal arts majors, but I don't think that's what you mean.
DOT 3, DOT 4, and the latest, DOT 5.1 are polyethylene glycol AND OTHER glycol mixtures. The mixtures differ among the grades, and among manufacturers. There ARE chemical differences, though like water and alcohol, the substances are miscible in all proportions.
I have now read a good part of:
http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.aspx?section=571.116
Which sets the standards for brake fluids and for their testing.
The document describes something called "mineral oils for vehicular hydraulic systems," and emphasizes the differences between these oils and DOT 3, 4, and 5.1 fluids. Specifically, it points out that that material (name is descriptive of source and application), which was used in older vehicles with drum type brakes, would degrade the plastic parts (the specific plastics are named in the article) in modern brake systems, resulting in damage not only to the plastic parts, but ultimately to the metal parts of the braking system as well.
Consumer booklets (owner's manuals) for most vehicles carry a warning to use only a specific grade of brake fluid. For example, my Toyota specifies DOT Type 3, while my VW camper ('91 VW Vanagon GL Campmobile) specifies DOT Type 4 (it does not mention Type 3 David). BTW, the Toyota is 16 years younger than the VW. Both warn against damage to the braking system if a different fluid is used. The VW booklet specifically mentions not to use Type 5 (Silicone based fluid), as David thought it probably would.
I have also read the web pages of several brake fluid manufacturers where DOT 3 and DOT 4 are evidently treated as one and the same for practical purposes, with some not carrying a DOT 3 fluid. Such manufacturers market their fluid as DOT 3 and DOT 4, meaning that it meets the minimum standard for both.
I now believe that my strong prejudice against substituting one brake fluid for another derives from such car manufacturers warnings, and from having lived through the transition from "mineral oils for vehicular hydraulic systems" to DOT 3 and DOT 4. But I will continue to use the specific DOT standard my particular vehicle calls for.
Does that serve your needs, Michael?
David McNeely
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