Re: {Chrysler 300} Hydraulic brake lamp switch

["mgoodknight@xxxxxxxx" <mgoodknight@xxxxxxxx>]

I too have explored several failed brake light switches in hopes of ending the unfounded belief that silicone fluid was the culprit.  I have a '55 Chrysler 300 and a new STANDARD MOTOR PRODUCTS switch ( made in Mexico) was the subject.  That switch lasted only a little more than a year (I use the car almost daily, but for only a few miles)  and I was terribly trouble over such a short life.  Upon disassembly of the switch I discovered that the "dry" chamber where the contacts are located had filled with fluid causing a liquid lock disallowing any movement of the diaphragm that should have been able to move the contacts to close. The failure mode was not a sudden event, but instead it was progressive over a few weeks when I noticed that it was taking progressively more brake pedal pressure to illuminate the brake lights.  I back my car into its garage mostly in the pre-dawn hours and I use the brake lights as back-up lighting due the the fact that the '55 does not have backup lights.  

 

I had previously disassembled an older version of the same switch, also a STANDARD MOTOR PRODUCTS sample from one of our parts car '55 Chryslers.  The failure of that switch was in fact a problem with the contacts, maybe a little burned, but mostly a little corroded.  Also the orifice in the threaded end through which a small volume of fluid must flow when the brake is applied had become somewhat filled with solid particles (apparently corrosion) from contaminated fluid and I believe that prevented fluid from entering to the diaphragm-------contact had been intermittent, sometimes lights worked and sometimes did not.  Because of the orientation of the switch pointed it downward I feel that it was subject to such contamination.  Orientation might have been the only initial problem on that one making it susceptible to contamination.

 

Regarding the Harley Davidson version of the pressure switch, I've dismissed the idea of using it because I suspect it is not suitable for the higher pressure that we have in automobile hydraulic brake systems.  I have not explored one of those to confirm or dismiss my belief that it should not be used on my car..

 

---------------Marshall Goodknight     3n552650        also '06 Harley Davidson Road King Classic

Please note: message attached

From: "Dan Plotkin" <dplotkin@xxxxxxxxxxxxxxxxxxx>
To: "'300 Club'" <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: {Chrysler 300} Hydraulic brake lamp switch
Date: Mon, 21 Aug 2023 12:26:23 -0400

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• From: "Dan Plotkin" <dplotkin@xxxxxxxxxxxxxxxxxxx>
• Date: Mon, 21 Aug 2023 12:26:23 -0400

I found the following website post dealing with the untimely death of many pressure operated brake light switches. Many are under the impression DOT 5 fluid is the culprit. The switch I installed in 2019, a Harley Davidson switch failed last week. No continuity. The link below takes you to a fella who cut the failed switches open to determine what failed. He contends it has little to do with fluid type as the failure occurs in the dry side of the switch.

 

He says the contacts burn because with hydraulic activation the contacts are brought together slowly, the incandescent load is high and there is no wiping or self-cleaning action of the switch contacts. He says Volvo gave up on them along with every other mfg after 1967.

 

I have one in a 63 Ford that failed after 19 years of DOT 3. I have an original, never been out, on a 1960 Buick on DOT 3.

 

Options are to replace the switch and see if it will go 4 years like the last one, use LED bulbs, install a relay, or install a mechanical switch on the pedal arm as many of you have done.

 

https://www.sw-em.com/hydraulic%20brake%20light%20switches%20notes.htm

 

 

 

Daniel D. Plotkin

Licensed in MA, CT, RI, NH & NY

360 Bloomfield Avenue

Suite 208

Windsor, CT 06095

Office: 860-683-9000

Cell:  413-237-9629

Fax: 860-683-1600

www.northeastretail.com

 

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