Re: {Chrysler 300} Brake switch for silicone fluid

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On Apr 24, 2023, at 9:17 AM, mgoodknight@xxxxxxxx wrote:

Regarding brake light switches and DOT 5 fluid use we certainly have a mix of observations,opinions, and diagnoses. I too have had some failures and I have rejected the idea that DOT 5 was the cause. There are, no doubt , numerous manufacturers of those switches but my experiences have been limited to those made by Standard Motor Products, Inc. whose products have worked well for me for more than 5 decades. That said, my recent 2 failures were with newly manufactured (in Mexico) Standard brand switches. I have carefully disassembled both an old switch and one of the recent new ones and I found that the internal design was changed.

In both cases the contacts are NOT exposed to any brake fluid, but are enclosed within a sealed air chamber isolated from the pressurized brake fluid by a flexible diaphragm which is linked by a small pin to press a spring loaded plate against the two electrical contacts. A mechanical failure within the switch is the only way that fluid would ever enter the chamber where the contacts reside. This very old switch had failed because of an accumulation of rust particles and maybe other contaminants that had entered the small orifice through which the pressurized fluid must enter to move the diaphragm and contact disc. When cleaned out it was still a functional switch.

The newly manufactured switch was different only in that the diaphragm was made of different material.. The old one had a pressed-in springy brass disc which was stretched a bit and acted like the bottom of an old oil can so that it "snapped' the contacts together" when applied and then "snapped " back when released, The sealing was excellent and I believe not at all prone to failure. The new switch had a rubber-like material for the diaphragm and when I opened the "sealed" contact chamber I found it flooded with fluid that had leaked into it through poor sealing of the diaphragm against the body of the switch There was no rupture of the diaphragm. When the air chamber (contact chamber) became filled with fluid the diaphragm could no longer press the contacts together. Air in the chamber could be easily compressed, but the liquid filled chamber prevented that.

Early stages of the failure displayed a that a slight increase in the amount of brake pedal pressure was required to turn on the brake lights. As the next 2 or 3 weeks passed I had to press the pedal quite a bit harder to turn them on and soon they no longer worked at all. My experiences were with my '55 Chrysler 300 which I drive almost every morning in the early (not yet daylight) hours. I store my car in a shed that I back the car into each time I drive it and It is easy to see brake light function. I have no back-up lights and the brake lights are useful for me as I back into the shed. I depend upon them to work well.

The switch presently installed is also a newly manufactured STANDARD switch and continues to function well now for about 2 years.

---------------------------Marshall

---------- Original Message ----------
From: John Grady <jkg@xxxxxxxxxxxxxxxxx>
To: dplotkin <dplotkin@xxxxxxxxxxxxxxxxxxx>
Cc: "D.C. Mason" <petergriffinforpresident@xxxxxxxxx>, 300 Club <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} Brake switch for silicone fluid
Date: Mon, 24 Apr 2023 07:49:56 -0400

Hi ,

I got into this after a few failures , I took one apart by cutting as i felt at the time it was inaccurate and anecdotal story that DOT 5 (which i use always ) causes switch failure . But here were failures , and i never had a hydraulic switch fail before —,ever .

So inside the switch there was a white coating on the switch contacts . Further looking into it from EE perspective , there is some kind of chemical decomposition of the silicone oil when an intense enough arc happens in it . That probably means current level / heat when the contacts separate millionths of an inch as silicone itself is a very good insulator ( 40,000 v per .1” !) .

The problem is not unlike points , and current is maybe 4 A, ok in oil or apparently glycol , but chemically the arc does something to silicone oil leaving an insulating residue on the contacts .

So after seeing it myself , I admit to a 180 .

Contacts in silicone oil are a bad idea no matter what you do , one might envision sliding self scraping contacts etc etc but the basic problem is real . I expected a bellows or something but contacts them selves were in the oil . These were stock switches . Unless a bellows is used moving contacts out if oil is in a Harley switch , it has to deal with the residue .

( like batteries discharging on cement floors — also true— another 180 ) .

Best cure is microswitch on pedal box , V3 with a long arm is a good place to start to roll your own , — as it is a matter of when it fails ( number of operations ) not if .

Being rear ended because of no brake lights and you don’t know that is not a happy day .

Quick check watch ammeter when stepping you can see the jump .

John

Sent from my iPhone

On Apr 24, 2023, at 6:41 AM, dplotkin <dplotkin@xxxxxxxxxxxxxxxxxxx> wrote:

The Harley-Davidson hydraulic brake light switch works with Dot 5. I have had that switch in my 300f with Dot 5 since 2019 no trouble. I don't know anything about mixed reviews either I have not heard anybody else say a negative thing about it.

Danny Plotkin

Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------

From: "D.C. Mason" <petergriffinforpresident@xxxxxxxxx>

Date: 4/23/23 10:55 PM (GMT-05:00)

To: 300 Club <chrysler-300-club-international@xxxxxxxxxxxxxxxx>

Subject: {Chrysler 300} Brake switch for silicone fluid

Hello club,

In reviewing the email archives I read mixed reviews on the Harley brake light switch (P/N 72023-51D ) that is supposed to be silicone proof. Has anyone had good luck with a pressure switch or is the consensus to put a switch at the pedal? Lots of old cars used the pressure switch but guessing they are all prone to failure with Dot5….
Thanks,
D&K

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