Finally, after listening to the debate for years, ' thought I'd try DOT 5
myself last summer. Despite THOROUGH flushing, in less than 400 miles my
calipers were leaking. In 15 years and untold hundreds of thousands of
miles, I have NEVER had an MGB caliper leak. You can bet I was back on DOT
4 LMA (and new calipers!) in a matter of hours! I learned my lesson.
Allen
>From: Tab Julius <tab@penworks.com>
>
>Not to dig up an old thread :) but recalling the conversation on silicone
>brake fluid and all that fun stuff, and came across this on the
>mgcars.org.uk site....
>
>--------------------
>A Tip for all MG's with Pressure Type Brake Light Switches
>by Paul Kile, Fair Oaks, California
>
>For all of you with MGs that have pressure type brake light switches (
>MGA's and MGBs/Midgets with single circuit brakes) - DO NOT use silicone (
>DOT 5 ) brake fluid in these systems, unless you want to replace your brake
>light switch every three months or so. Although none of the recent debates
>on silicone fluid seem to mention this, I have had three brake light
>switches fail on two different cars, both using silicone fluid. Others on
>the Internet have noticed this also. It appears that the silicone fluid
>acts as an insulator and prevents the switches from making contact.
>
>The solution? Stick with DOT 4 fluid and change it yearly, or put in a
>mechanical type switch on the brake pedal.
>
>--------------------
>
>'s true?
>
>- Tab
>'78 B
>
>At 01:54 PM 8/30/99 -0700, Max Heim wrote:
>>No, I think you are a little confused. *Silicone* brake fluid has never
>>been accused of dissolving seals (or anything else). That is its chief
>>benefit. DOT 3 or 4 brake fluid is notorious for dissolving paint
>>everywhere it drips. It has also been known to dissolve the seals on
>>LBCs, *except* for Castrol GT LMA brand fluid. Why is this? Who knows?
>>DOT 3 and 4 are performance specs, not materials specs, so it is possible
>>that Castrol uses a different formulation than Pep Boys, Mechanics Brand,
>>etc. At any rate, there is plenty of evidence in on this subject, and the
>>recommendation is clear:
>>
>>Use exclusively Castrol GT LMA brand DOT 4 brake fluid, *or* completely
>>flush your system and convert to silicone brake fluid (DOT 5, any brand),
>>since silicone fluid is incompatible with the other variety.
>>
>>Note that DOT 5 is not an "improved" spec compared to DOT 4, it is merely
>>a different chemistry with different benefits. DOT 4 = higher boiling
>>point; DOT 5 = non-corrosive.
>>
>>Some people may not have had any trouble with "off-brand" DOT 4 fluid in
>>their MGs -- if so, congratulations, but be aware that there are many
>>different sources for brake system rubber components . The next time you
>>rebuild, you might not be so lucky.
>>
>>'nuff said!
>>
>>
>>James Nazarian Jr had this to say:
>>
>>>I have had dot 5 (silicone) in my brakes and clutch of my mg for about 5
>>>years now and I haven't had a single problem. My understanding is that
>>>the original and early replacement seals couldn't stand up to silicone,
>>>but that the newer replacement seals (within the past 5 years or so) are
>>>designed with a slightly different compound will have no problems with
>>>silicone. I don't know the difference in the two kinds of rubber or
>>>fluids, but I would guess it is related to the same properties that make
>>>dot 3/4 take off paint and dot 5 prevent paint from bonding. So far I
>>>haven't had any problems with the silicone, but I think there must be some
>>>truth to the rumor so I would make sure the seals in m/c and s/c are
>>>fairly new.
>>>
>>>James Nazarian
>>>'71 B roadster
>>>'74 BGT bastardization with big aluminum heart :)
>>>'63 Buick 215 cubic inch 'heart'
>>>
>>>On Sat, 28 Aug 1999, Larry Hoy wrote:
>>>
>>>> Ken Payne said (in part)
>>>>
>>>> > I used AP550 for a while ... and [it] seemed to be harder on some seals.
>>>>
>>>> So can anyone tell me about rubber seals?
>>>>
>>>> What's the deal with certain brake fluids destroying certain fluids?
>>>>
>>>> Is this problem a thing of the past? Some how I gotta think that today's
>>>> brake rubber parts must be compatable with DOT 3, 4, and 5 brake fluids?
>>>> Can anyone enlighten me?
>>>>
>>>> Larry Hoy
>>>>
>>>>
>>>
>>>
>>
>>
>>--
>>
>>Max Heim
>>'66 MGB GHN3L76149
>>If you're near Mountain View, CA,
>>it's the red one with the silver bootlid.
>>
>>
>>
>
mg-mg-mg-mg-mg-mg-mg-m-gmg-mg-mg
Allen Bachelder
'73 B - "done"
'76 B - daily driver
'73 GT - awaiting front wings
'65 B shell - awaiting paint
'67 GT - awaiting everthing
'57 ZB - parts car or resto-candidate? - awaiting decision
'49 YT - in "progress"
mg-mg-mg-mg-mg-mg-mg-mg-mg-mg-mg
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