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Investigating the failure of brake switch with DOT 5 brake fluid (silicone).

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  • Brakes: Investigating the failure of brake switch with DOT 5 brake fluid (silicone).

    It is a subject much discussed. I never took it too serious until it happened to the only vehicle I have using silicone brake fluid. My 1951 Land Cruiser.

    I saved the old brake switch. In an attempt to determine why it failed, I began to study its construction. For years, I sold all sorts of fluid pressure devices... pumps,cylinders, gauges, pressure regulators, and fluid controls. For the most part, they are fairly simple devices. Their complexity usually involves chemical resistance involving specifications to meet what they are exposed to. Also, pressure limits to meet safety standards for the operating pressures of the system for their intended use.

    Although I had never opened up a simple old fashioned brake switch, I had a good idea of how they were constructed. I figured that a brake switch involved some sort of diaphragm seal, a contact (s), and some kind of spring (stand-off) to keep the contacts separated until pressure was applied to close the circuit.

    I used a continuity tester to see if I could manually close the contacts (thinking that the diaphragm had failed causing the switch to not respond to pressure.) I used a small ball-end allen wrench to manually push in on the switch. No matter how hard I pressed, the switch would not show continuity on the meter.

    So, I decided to open up the switch. Any of you who have held one of these switches in your hand knows, they were not intended to be dismantled. Since I don't have a metal lathe, I improvised by laying a small bench drill press on its side and secured the threaded end of the switch in the drill chuck.

    I adjusted the belt on the drill press to run at its lowest speed. Then, carefully used a hacksaw with a fine tooth bi-metal blade to cut the switch housing at the crimped end. The picture below reveals the simplicity of the switch.
    Click image for larger version

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    Just as I thought, the switch consists of a metal housing, Bakelite (hard plastic) insulator, a diaphragm, a thin copper wafer (main movable switch contact) spring, and the two copper conductors to which the brake light wires are connected.

    What surprised me was that the diaphragm was in great shape. Also, the side away from the fluid, was surprisingly dry. I was expecting to find a damaged diaphragm and the contact side full of brake fluid. My conclusion was that the mechanical function of the switch was intact and functioning as designed.

    However, if you will look closely at the copper wafer, you will notice a couple of small crescent shaped dark spots corresponding to the fixed copper contacts imbedded in the bakelite insulator. Those contacts have similar spots of corrosion as well.
    Click image for larger version

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    My conclusion is that there must be some tiny bit of silicone brake fluid getting by the rubber diaphragm. It is not much, but must be enough to cause some chemical reaction in the presence of electrical current to cause the corrosion to form. Apparently, the corrosion itself is non-conductive, and once the contamination
    reaches a certain build-up, it will not allow current to flow, even when the contacts are mechanically pushed together under pressure.

    That exposes the problem. All we need now, is a solution. I wonder if there is some type of lubricant or chemical that would prevent the corrosion? Of course, it is not something we could solve in our back yards. It will have to be addressed at the point of manufacture.
    Last edited by jclary; 04-23-2016, 04:47 AM.
    John Clary
    Greer, SC

    SDC member since 1975

  • #2
    Good sleuth work!

    Ron Francis makes a silicone compatible switch...

    http://www.ronfrancis.com/prodinfo.asp?number=SW-32

    Also Painless Wiring and Harley Davidson. Probably others.
    Dick Steinkamp
    Bellingham, WA

    Comment


    • #3
      Excellent work John! This may be why that some Members, I believe Jon Myer is one, recommends a drop or two of DOT 3 or 4 Fluid in the switch before installing a New switch on a Dot 5 Silicone equipped Car.

      If that DOT 3 stays in there, it would prevent the DOT 5 from damaging the contacts and could actually extend the life or permanently save it.
      You also could add fittings to those Switches that mount other than upside down, to make them fit that way helping to hold the DOT 3 fluid in.
      StudeRich
      Second Generation Stude Driver,
      Proud '54 Starliner Owner

      Comment


      • #4
        Good job John.

        A thought, Silicon is the material found in electrical connectors to keep them from corroding. It doesn't like moisture (hydrophobic) and generally doesn't allow moisture infiltration. It would probably be better to pack the switch with silicon to reduce the corrosion but as opposed to Dot 3/4/5.1 it may not adsorb the moisture that enters the switch but just let's it reside there and corrode the contacts. Packing the switch with silicone would keep the moisture out. I'll bet a piece of copper placed in Dot 5 will be there for years with no corrosion. Bob

        Comment


        • #5
          As a side note... it may also be a quality issue. I have tried various brands of this switch on my cars and get between 6 months and 5 years depending on the brand. I also know of at least one original Studebaker switch that has been in service on a silicon fluid equipped car since 1978 and is still working well. Avanti Motor Corporation switched to silicon fluid around the same time and didn't have a problem. Along the way something has changed.

          Chris.

          Comment


          • #6
            I've had this same problem on my '33 Ford. In the Hot Rod World, the suggested solution is to run the brake light switch with a relay. I did just that and it has been 5 years since I made the change and no problem.........yet. Prior to that it was almost an annual event and the location under the floorboard in a very tight set up was a bear to change. BTW Harley Davidson sells a switch that they claim is silicone friendly. Why should the rely make such a difference? I have no idea, but to date it is working for me.

            Comment


            • #7
              Many years ago, I found that the best solution for my '63 Avanti (with DOT5) was to simply install a mechanical stoplight switch. All this required was fabrication of a simple bracket to mount the switch above the brake pedal. I ran the wires out to the harness at the original switch location and used bullet connectors to plug in. This left the original wiring unmolested. End of problem. An additional benefit is that the brake lights come on sooner than with the pressure switch.
              Jim Bradley
              Lake Monticello, VA
              '78 Avanti II
              sigpic

              Comment


              • #8
                Giving this a little further thought...it wouldn't surprise me if these switches are not swedged (sealed) at final assembly in open atmosphere. That would entrap oxygen inside the contact chamber. The solution could be to enclose the final assembly in a nitrogen filled chamber. That would exclude oxygen and prevent oxidation that results in the corrosion seen in these switches.

                I was once tasked with solving a problem a customer was having with dispensing an adhesive in a manufacturing operation. The material was very unstable when exposed to air. Attempts to pump it resulted in seized pumps, plugged lines, and clogged nozzle tips. My solution was to dispense it using a pressure pot pressurized with compressed nitrogen instead of compressed air.

                Regarding these switches, the flaw in my theory is that if entrapped "normal" air is the culprit, it would be a common failure regardless of what type brake fluid is used. Therefore, there must be something else going on in the presence of DOT 5. I would like to have a failed brake switch from a system still using DOT 3 fluid and see if it is due to the same kind of corrosion. Problem is, I can't recall ever having a switch fail on regular brake fluid. I've had wires to fail, and bulbs burn out, but can't recall a single incident having to replace a switch.
                John Clary
                Greer, SC

                SDC member since 1975

                Comment


                • #9
                  John, if you decide to get rid of the hydraulic switch all together, here is how I converted my '54 sedan to a mechanical switch: http://forum.studebakerdriversclub.c...e+switch+sedan
                  Paul
                  Winston-Salem, NC
                  Visit The Studebaker Skytop Registry website at: www.studebakerskytop.com

                  Comment


                  • #10
                    Originally posted by jclary View Post
                    Giving this a little further thought...it wouldn't surprise me if these switches are not swedged (sealed) at final assembly in open atmosphere. That would entrap oxygen inside the contact chamber. The solution could be to enclose the final assembly in a nitrogen filled chamber. That would exclude oxygen and prevent oxidation that results in the corrosion seen in these switches.

                    I was once tasked with solving a problem a customer was having with dispensing an adhesive in a manufacturing operation. The material was very unstable when exposed to air. Attempts to pump it resulted in seized pumps, plugged lines, and clogged nozzle tips. My solution was to dispense it using a pressure pot pressurized with compressed nitrogen instead of compressed air.

                    Regarding these switches, the flaw in my theory is that if entrapped "normal" air is the culprit, it would be a common failure regardless of what type brake fluid is used. Therefore, there must be something else going on in the presence of DOT 5. I would like to have a failed brake switch from a system still using DOT 3 fluid and see if it is due to the same kind of corrosion. Problem is, I can't recall ever having a switch fail on regular brake fluid. I've had wires to fail, and bulbs burn out, but can't recall a single incident having to replace a switch.
                    A couple more thoughts. I'll bet swagging doesn't provide an air tight seal between the metal and hard plastic unless there is a provision for a seal or sealant at that interface which is not obvious to me in the pictures. H2O is a tiny atom and it can get a lot of places. Like through the plastic wrap you have around food in the fridge so a swagged interface is a weak barrier.

                    Silicone has been a material of choice for many years as a di-electric fluid/grease to resist corrosion of electrical connections.

                    I've had several brake switches fail with Dot3/4 over the years but not Dot5. That's not a large data base as my cars with Dot5 are treated much better than the ones with Dot3/4.

                    It's possible that with the hydrophylic Dot3 on the other side of the diaphram moisture will permeate into it while the Dot5 won't allow it. I'd like to see them pack the switch with Silicone fluid and that should be the end of those issues unless there is something in the formulation of Dot5 that causes corrosion.

                    Bob

                    Comment


                    • #11
                      Ideally, a pressure switch with a welded stainless diaphragm would solve this. Someone must make one for the automotive market. Otherwise, there are lots of industrial switches to use - at a price.

                      Adding the relay seems to be a common way around the problem. Here's a link to a page where the guy used a relay with a capacitor across the contacts and a diode on the coil to prevent arcing.
                      http://www.omgtr.ca/technical/brakel...lightrelay.htm
                      Gary Ash
                      Dartmouth, Mass.

                      '32 Indy car replica (in progress)
                      ’41 Commander Land Cruiser
                      '48 M5
                      '65 Wagonaire Commander
                      '63 Wagonaire Standard
                      web site at http://www.studegarage.com

                      Comment


                      • #12
                        I like your thinking Bob. Another thing has occurred to me. When I switched over to DOT 5, I drained and cleaned everything. I replaced the flex hoses, and fabricated new metal brake lines. I either rebuilt, or replaced, the master cylinder, and all four wheel cylinders. However, I think I merely re-installed the brake switch. It is possible that the brake switch was the one that left the factory in 1951. At the time I did the conversion, the car only had around 58,000 miles.

                        It is easy to see how incorrect assumptions can be concluded from such crude unscientific observations. I like the alternative mechanical switch solution that Paul and others have made. I have several of those switches. Surely, with the early automatics like my Land Cruiser, having those wide double brake pedal shafts...room to safely install the switch shouldn't pose a problem.
                        John Clary
                        Greer, SC

                        SDC member since 1975

                        Comment


                        • #13
                          What about using a dab of silicone caulk on the exterior of the switch where the phenolic meets the aluminum body in order to prevent moisture from entering from the exterior. I am guessing that since the DOT3 would ABSORB the moisture, it was less of an issue because it would draw the m,oisture AWAY from the contacts, whereas, now, it allows the moisture to stay inside the switch and corrode the contacts.

                          Just my $0.02.......
                          Dis-Use on a Car is Worse Than Mis-Use...
                          1959 Studebaker Lark VIII 2DHTP

                          Comment


                          • #14
                            John, how long was the dot 5 in there before the switch failed?
                            Dan

                            Comment


                            • #15
                              OR...drill two small holes in the opposite sides of the switch, and fill the switch full of silicone grease...

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