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.
>
>
>
|