Hi:
I thought that I would share with you some brakelite switch/silicone brake
fluid tips.
The reason that this fluid causes the problem that you describe is: the
silicone fluid causes therubber cup to swell slightly. This causes a
partial blockage of the return hole in the M/C. THis in turn leaves
residual pressure in the system which leaves the brake lite switch stick in
the on position. These switches were not designed to stay on for long
periods of time, so they burn out.
The fix for this is to dismantle the M/C, and remove the piston. Chuck it
up in a lathe, and remove 50 thousands of an inch from the rear of the
piston.This allows the piston to retract far enough to alleviate the
problem. I have done this procedure on many occasions, and it works.
I have silicone brake fluid in three LBCs, and no further problems.
Cheers:
Skip.............t 09:44 AM 11/2/97 EST, ROBERT G. HOWARD wrote:
>Eric,
> I replaced the original switch on my '52 TD this summer, thinking that
>the silicone fluid first installed in 1980 or thereabouts had caused
>premature failure of the brake switch this year. The switch was sticking
>closed/on.
> New switch worked no better.
> Turned out that the trouble was the MC not releasing its pressure
>promptly. The brakes were releasing well enough, but there was excess
>residual pressure and the brake light switch was staying on. Brake
>light switches were OK all along. If silicone fluid were to cause
>premature failures, one would suppose that sometime in 17 years the
>switch(es) would have failed. Instead, it was either the cheap curved
>washer or the cups in the MC that were replaced in 1958. This all
>should have been taken care of under the Warranty anyhow.
> Still, reading the number of concerns raised about these pressure
>switches makes me wonder. Has anyone converted his MG to a push or pull
>brake switch that's operated by the pedal movement? Both the GM beauties
>in the driveway here are so equipped.
>Bob
>
>On Sat, 1 Nov 1997 17:19:38 -0800 ejrussell@sprynet.com writes:
>>On Sat, 1 Nov 1997, Art Pfenninger <ch155@FreeNet.Buffalo.EDU> wrote:
>>> Any idea of what car the replacement brake light switch might
>>be
>>>from, I'd like to try a switch that lasts at least a year.
>>>...Art
>>>
>>>On Fri, 31 Oct 1997 ejrussell@sprynet.com wrote:
>>
>>>> Check the hydraulic brake light switch under the hood
>>(bonnet). They
>>>>don't last forever. If you have 12 volts going into the switch
>>(ignition ON)
>>>>connect the two wires at the switch together (temporarily). If the
>>brake
>>>>lights are now on (ignition ON) the circuit is OK and the switch is
>>bad. It is
>>>>a standard US thread, I get replacements locally. I think the
>>original has
>>>>small screws to attach the wires, I made short jumpers to adapt to
>>what I
>>>>bought locally...
>>
>> Art, I don't know what car the switch is from but it must be a
>>standard
>>design. I brought the failed original to my (very helpful) local auto
>>supply
>>store. They glanced at it, pulled one off the shelf and I was all set.
>>The only
>>difference is that the original has two screw terminals and the
>>replacement has
>>two bullet connectors. (Or is visa-versa?) I made two short jumpers to
>>adapt the
>>MGA harness to the replacement switch. The one in my spare parts bin
>>now is:
>>BORG-WARNER # S-194 I don't understand why they don't last very long,
>>I get
>>leary after a couple of years. I recall reading someone's opinion that
>>silicome
>>brake fluid (which I have used for 10+ years) somehow shortens the
>>life of these
>>switches which I don't understand. I have found that quickly changing
>>the switch
>>causes only a tiny loss of brake fluid and no air gets in the line. I
>>have
>>wondered whether the position of the switch (contacts up) leaves a
>>small air
>>bubble inside the switch allowing it to deteriorate somehow...? I have
>>had the
>>same style switch in my '41 Chevy truck for 4-5 years with no trouble.
>>It is
>>mounted horizontally, my theory is that the brake fluid (also
>>silicone) can
>>somehow get all the way inside therefore it is surviving. Does that
>>make any
>>sense? Perhaps you could test this theory for us by rolling your car
>>onto its
>>side when you replace the switch!! Maybe the MG just prefers to keep
>>the Lucas
>>heritage alive!
>> Did you know that the Queen knighted Mr Lucas for his
>>invention of
>>intermittent windshield wipers? They conveniently neglected to mention
>>his
>>earlier inventions: intermittent headlights, intermittent ignition,
>>etc!!
>>
>> Eric
>> Bridgewater, MA
>> <ejrussell@sprynet.com>
>>
>
>
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