I'm on my third brake switch in as many years. Tried different brands, all with the same results: failure. So I machined off the crimp flange on the last one because I needed to know how it works, and why it failed. Pretty simple design with the brake fluid pushing against the rubber washer, which pushes the disc to make the contact. There's a small spring, not shown, that sits in the center. Anyways, it appears the contacts arch each time the brake is applied, and over time builds up gunk (not sure of the technical term) which inhibits the electric flow. The two external leads are brass, but the disc appears to be copper. Is this a dis-similar metal thing? Just wanted to show anybody interested why these fail, and why I'm switching to a mechanical lever switch.
Was it dry in there when you took it apart? Most times brake fluid leaks by the seal and messes it up in there. The next step is brake fluid visibly leaking out. New type brake fluid is more aggressive then the older type. That is why most cars since the 60's use mechanical switches.
if you use a relay less amperage would travel through the switch increasing the life of it. there are different quality switches too. even in Echlin line. last time I bought the best one possible and it still works .
I have a Napa switch in my Ford, the one that came with the CPP proportioning valve leaked fluid right away. I wonder if a tin-lead coating on the disc would have helped what you see going on with your switch, looks quite oxidized.
Bob, Thanks for showing how that brake switch functions. I wonder if it could be modified so that it threads together and is sealed with an o-ring? It would be neat to make a proto-type.
I would bet that the original switches had a solid copper disk to minimize transfer issues. If the replacements are not holding up, I would be inclined to look for an industrial grade Hobbs switch that would replace it or just do away with it completely with a mechanical switch on the pedal.
high current flow burns , see the pulled material on the contacts ?? . and that's real copper ( not a alloy to cheapen it out ) use it to operate a relay . some of the old ones I took apart has silver plated contacts and the copper disc .
Are you using DOT 5 brake fluid? FWIW and this is only what I was told. The hydraulic pressure switches are prone to failure when used with silicone fluid. A retired engineer who also was a high end car collector (think V-16 Cadillacs) that I was acquainted with came in and bought Harley Davidson brake light switches and used them on his cars. He said that the H-D ones were designed for use with DOT 5 along with DOT 3 & 4. While I cannot swear to that, I do know that they have been using DOT 5 since the 80's and my 82 FLH has had the same switch in it since at least 1998.
I steal them out of all the old ford cars(mainly falcons) and keep them when I dispose of the master cylinder or whole car. It seems that the original ford ones are pretty durable. At least for me they are. My 64 Ford Falcon one is the original and still works great. I have more problems with the "bullet" wire ends that ford used to press on the studs coming loose.
I've had an original switch on my mostly stock '37 Chevy coupe ever since I owned it (16-years). I've put at least 30k miles on it in that time and the switch still works fine. I did change it over to DOT 5 (silicone_ brake fluid when I first got the car. The new switches are junk, apparently with the exception of the H-D ones.
it has to do with the time it takes to turn your brake lights on and off. its not a snap switch like a toggle or a light switch. the hydraulic pressure moves a bit slower and is variable so there is plenty of time to arc and destroy the contacts.
I'll second the Harley switches; they're very reliable and not much more money than the crummy parts house versions. The Harley dealer is also a great place to get tail/brake lamps. They're a bit brighter, and have a heavy-duty filament that withstands vibration. The lamps are a different 'number' compared to an 1157, but will interchange. One other thing to check; make sure you don't have high-wattage lamps. The PO of my avatar fitted a 'high visibility' 55W brake lamp kit (!!!) and I went through a couple of heavy-duty mechanical switches before I discovered them and changed the lamps out. The irony is they weren't any brighter than the regular lamps because of how they fit...
This one was for a Harley, but not branded as such. Currently, I have the NAPA switch, so we'll see if it makes it thru the summer. I'm using LED tail lights.
I never use hydraulic switches. I use the old Chevy truck style lever switches, and have never had one fail. I hate bleeding brakes, so why would I want to put an easy-to-fail part right up at the top of the brake line system? You'd have to bleed all four corners. No way!
Arc-over is your main issue. You can resolve it in several ways: 1) Put a 1Mfd@25vdc capacitor across the connections. 2) Use a relay or some other pass device to reduce current through switch. 3) Use a mechanical switch, which might be just as bad. 4) Change stop lights to LED type if you have separate turn signal bulbs.
I've had a 59 chevy truck for 4 decades, I've had to replace that switch a few times. But not every year!
There's no need to bleed the brakes after replacing the brake switch. Seems like it would be, but it's not. I replaced the original brake switch on general principles though keep it as a spare. It had started to get "lazy" and was a little slow on the draw. The Harley switches are supposed to be a little better than the drug store replacements. Bob Drake or somebody like that makes a "special" version that is supposedly faster to trip, with a special price, too natch. Haven't seen the need.
I have mine wired (under the hood on fender well) long enough so I can bring the wires inside the car and attach it to a pedal switch if I need to.
I agree that brakes are not likely to need bleeding, given the typical location of a hydraulic switch, and no cycling of the M/C while changing the switch. Perhaps the switch itself should be bled a bit, but there is no likely reason for air to enter the brakes lines when the switch is changed out. Ray
Well, we all make mistakes. LOL! Kidding! Seriously, I am always learning, always looking to do things correctly, and safely. I'm also always looking to cut out big time wastage. "Work smarter, not harder". Can you post a scan of the task for replacing the brake switch from the '56 manual? It's not really described in detail in the '64 Ford manual, other than "remove wires". That's it. Well it's easy to slip over the line into silliness here too. If you look at the way these (Ford) things work, due to its location it's like opening up the reservoir cap, maybe some master cylinders are different. I shouldn't have made a blanket statement, for all master cylinders though, on my particular application swapping the brake switch out tends to push fluid out, if anything. It takes less than a second. If you think it's necessary to perform a 4 corner bleed after that, knock yerself out. For the record I don't personally need the "We're All In This Together" lecture, the entire braking system has already been replaced to include drums, springs, wheel cylinders and shoes on all 4 corners, all new steel hard lines, master cylinder, hoses, resurfaced the brake backing pads, all new shocks, leaf springs and wheel bearings, steering linkage and tires. And a new brake switch! I did leave the pedal alone though. The fucker stops on a dime. Truth be told I'm pretty retentive when it comes to mechanicals myself but I try not to make a big production out of it. If I thought it was necessary, in that instance I would have bled the system. If I'm way off base here - I'll bleed the brakes. If I truly put out bad dope.
I know Ford came out with the hydraulic switches for many years, along with many other applications. When it came down to choosing a brake light switch for my hotrod, I used knowledge of this and observations from many years. When I was an Air Force mechanic, the Emerson 25K aircraft cargo loaders our squadron had had a common failure---the brake light switch leaking fluid. It hung under the master cylinder and the machine was equipped with hydraulic brakes. Check one-failure. A buddy built a 66 F100 and went back with the same factory style hydraulic switch. He could feather the brake pedal and keep the brake lights from coming on. Check two-could cause traffic induced failures. I ended up using the Ron Francis style plunger switch on my A chassis with under the floor equipment. My two cents. And the relay suggestion is a good idea, because the dead switch looks like load induced contact failure.
The one thing I don't really like about them, they are "hot" all the time. Haven't really heard of too many incidents with the old school switches, but there have been some fires associated with leaks on late model OT vehicles. I'm not too paranoid about much, except Fire. Supposedly they don't play well with silicone brake fluid. I've never actually had one fail, but it became real slow to light after a hard panic stop so I replaced it. Avoid the "we sell the cheapest chinesium replacement parts" drug store auto section version. FleaBay has some good old NOS probably. Harley-Davidson uses the same switch as well, and Ron Francis sells a boutique version, silicone ready, for all the cork sniffers out there. Supposed to trip at a lot less psi than the stock type.
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