| fordmerc | -- 05-07-2012 @ 11:11 AM |
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My brake lights do not light unless there is almost full pressure on the pedal. Braking to slow down does not make the light go on, thus creating a lack of warning to those behind me. This is a "new" switch and master cylinder. Is there an explanation for this and is it fixable?
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| c-gor | -- 05-07-2012 @ 12:24 PM |
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What type of Brake Fluid ars you using?
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| CharlieStephens | -- 05-07-2012 @ 12:32 PM |
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c-gor probably should have said if you are running silicone brake fluid this is the type of problem you can expect with regular brake light switches. Ron Francis Wire Works, (800) 292-1940, wire-works.com, sells a switch designed to work with silicone. I think he also sells switches designed to run on low pressure. Charlie Stephens
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| fordmerc | -- 05-07-2012 @ 5:21 PM |
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Yes, I used silicone fluid! It certainly has been a bad choice. I had lots of leaks in the beginning and the thought of changing switches is devastating! Nevertheless, I will probably have to do that. Thanks for the source.
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| Stroker | -- 05-07-2012 @ 5:32 PM |
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Silicone fluid has its' place, especially in seldom driven museum cars that live in a humid climate. Changing the switch however, shouldn't be particularly traumatic, unless you have a phobia regarding getting under your vehicle. Which is better; flushing your brake system regularly, or using silicone? I don't, as I prefer the former, but for some it is the ultimate solution.
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| trjford8 | -- 05-07-2012 @ 8:35 PM |
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If you are not concerned about being strictly stock you can use the lever type mechanical brake switch that was used on the early Chevy pickups.It mounts under the floor and goes on as soon as you move the pedal. I use them in all my old Fords.
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| fordmerc | -- 05-08-2012 @ 5:06 AM |
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My car is 99% "correct". Even that low pressure switch doesn't look original because of a strange electrical connector. Nevertheless, I'd claim safety as the reason for changing the switch. My aversion to getting under the car is only on principle, since everything seemed to be OK until friends behind me pointed out the flaw. I agree that the switch change is preferable to frequent bleedings (of me or the brakes). I'm surprised that other amateurs like me haven't complained about this issue: why does silicone fluid operate at lower pressure than other fluids? That is not intuitive.
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| Stroker | -- 05-08-2012 @ 6:27 AM |
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fordmerc: Yeah, I agree that it is not intuitive. I have never used silicone fluid, as I have heard that on a frequent "driver", it is less lubricious; leading to premature wear of the brake cylinder and master cylinder cups. I've never sawed a brake switch apart, but I'd assume it only contains a diaphragm. Perhaps you simply got a bum switch with a pinhole in the diaphragm. The only good thing I've heard about silicone is that it is non-hygroscopic.
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| TomO | -- 05-08-2012 @ 7:28 AM |
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I have been using DOT 5 for over 30 years and I use the stop light switch from NAPA. They work well for about 5-8 years and then I have to change it. If you have a new switch, I suspect that you may have a small amount of air still in your system. DOT 5 gets very small bubbles of air in it that are hard to bleed out. When I do a repair on the brake system, I bleed all of the visible air and then let the car sit for a couple of days to let the air settle into larger bubbles and bleed the system again. Tom
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| supereal | -- 05-08-2012 @ 10:17 AM |
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The key to your problems is likely the "new" switch. The foreign made switches are prone to problems, if they work at all. You are right about silicone fluid being a headache. A good replacement switch is the one used on Harley Davidson motorcycles. It is silcone proof, and seems to operate at a lower pressure than the standard switch.
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| 51f1 | -- 05-08-2012 @ 5:32 PM |
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But the Harley switch has a different type of connector. Richard
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| supereal | -- 05-09-2012 @ 9:41 AM |
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The terminals on the wires may have to be adapted, but that isn't a big deal. When you buy the switch, ask for the mating plug, if you don't have an assortment of terminals on hand. The switch is a simple "normally open" type, so the orientation of the connections isn't important.
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| 41fatso | -- 05-11-2012 @ 5:55 AM |
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I am a strong advocate of silicone brake fluid, as I have used it in my 41 deluxe coupe for 14 years. I've never had to service my brake system other than change brake shoes occasionally. My car is regularly driven. I too have had the problem with my brake light switch. Ron Francis seems to be the way to go in getting a new switch. Which I plan to do. Thank you all for your help.
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| 37 Coupe | -- 05-11-2012 @ 6:37 AM |
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While I was ordering wiring from Tyree Harris I had him make up two short jumpers,probably 6 " long or so,green that connected to my original brake switch terminals and the Ron Francis switch. This so I didn't have to cut or alter my new wiring.
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| fordmerc | -- 05-19-2012 @ 5:08 AM |
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Follow-up: I replaced the old switch with a low-pressure switch from Ron Francis: PHENOMENAL DIFFERENCE!! Now a light tap on the pedal lights up the lamps. Based on all comments, a low pressure switch seems essential with silicone fluid.
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| 40cpe | -- 05-19-2012 @ 9:44 AM |
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Not to have any misconceptions about silicone fluid: It does not apply the same or more pressure to the brakes with less pressure applied at the pedal than any other hydraulic fluid under the same circumstances. Likewise, a switch will operate at the same pressures with any fluid. When the fluid migrates to the switch side of the diaphragm is when the switch requires abnormally high pressure to operate.
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| thirtysixford | -- 05-19-2012 @ 3:09 PM |
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Just a FYI I bought the same switch RF sells for $40 for $17.50 on eBay from autorewire. Just do a search.
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