>From mercury.lcs.mit.edu!tr8-request Mon Jun 6 16:20:51 1994
>
>From: whs70@cc.bellcore.com (sohl,william h)
>>The following is about my TR-250, but the comment is generic to all
>>Brit cars:
>>I just bought a new master cylinder from Moss (the box was labeled
>>Beck/Arnley) and the brake fluid reservoir cover states to use
>>only DOT 3. Now that flies in the face of most conventional
>>wisdom that says british car hydraulics need DOT 4 (LMA, Girling,
>>etc.) In any case, I opted for the DOT 5 too. I had that in
>>the system before with no problem.
>>
>>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.
>>
>>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).
>
>Now I'm really confused. I always thought that DOT 4 is just like DOT 3
>glycol fluid only with a higher temperaure rating. In other words, I don't
>see how DOT 3 would encourage rubber failure of any kind when you've got
>a system designed for DOT 4, or how it would make any difference at all
>if you're just using it for the clutch (not a whole lot of heat compared to
>brakes). Likewise, DOT 4 simply supercedes DOT 3, so if something (likely
>old) specifies "only DOT 3", then DOT 4 should be just fine. If I'm wrong
>I'd really like to know.
>Jody
Actually, the brit-cars legend precedes the DOT X labels. Back in
the 50s/60s, it was accepted practice not to use the USA domestic
brake fluids in a British car because (as the story goes) the British
car's rubber brake components were made using a different type
of rubber (i.e. live rubber) than similar components in American
vehicles. The legend has it that use of American brake fluid in
a British car's brake system would lead to disintegration of the
Brit Car's rubber brake components (seals, etc.)
All this was well before the advent of silicon (DOT 5) fluids, so
my comments are, indeed, related to DOT 3/DOT 4 (the girling LMA
fluid containers are labeled DOT 4 as I recall.)
That's it, additional comments, thoughts, actual stories, and
what have you welcomed.
-----------------------------------------------------------------------
Bill Sohl (K2UNK) BELLCORE (Bell Communications Research, Inc.)
Morristown, NJ email via UUCP bcr!cc!whs70
201-829-2879 Weekdays email via Internet whs70@cc.bellcore.com
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