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.
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.
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.
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.
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.
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.
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