Brake pedal contact or mercury switch

[Michael Oritt]

Has anyone replaced the standard hydraulic brake switch with one mounted on the brake pedal--activated either by mechanical contact or a mercury switch?

 

[CessnaTPA]

Yes I just recently installed a micro switch in parallel with the pressure switch that the brake pedal triggers. I can take some pics if you like.

 

[Michael Oritt]

I would appreciate seeing them and/or getting info on where you got the switch. This is for one of my race cars, not for my Healey, and it has an organ-type brake pedal--that is, hinged on the floor as opposed to suspended.

 

[Randy Forbes]

A micro-switch (mechanical) is perfect for the application. While the pressure switch(es) in my own car are still functional, I have put industrial-type (sourced from Grainger's) in other cars before.

There are a myriad of styles to choose from, and there must be something perfect for your car!

https://www.mcmaster.com/#micro-switches/=15tnq33

 

[roscoe]

I agree. We use micro switches on baggage, cargo and passenger doors on helicopters and airplanes. One small piece of advice is that you should have a secure mount for the switch that doesn't flex or loosen up. If you add a clamped on tab or similar piece to push the switch when the pedal is depressed make sure it it never going to slip, bend, or break. The other issue is checking the throw of the lever to be sure the switch you select will be activated at the lightest of pedal touches , yet have enough throw to allow full pedal deflection in emergency conditions. The switches go from being the best thing since sliced bread to a real pain in the neck when they slip out of adjustment and no longer work as they were intended. I like the idea of having it in parallel with the original switch.

 

[vette]

Michael, it sounds like your brake pedal is pivoted below the floor so that where your pedal creates a push the opposite side of the pivot creates a pull. At this point you can mount a small switch that has a pull plunger instead of a push plunger. Then mount this pull switch where the pulling part of the pivot will pull the switch plunger. Also use a spring (fairly stiff) to link between the switch plunger and the pedal arm. Many manufactures use a variety of switch configuration at the brake pedal some will pull some will depress.

 

[Michael Oritt]

All--

Thanks for the input and I should have been more descriptive in my first post. The pedals are a standard Wilwood set #340-12411 and I'll have to devise an arm that activates a switch on push, the challenge being much as Roscoe describes: having it activate on slight braking effort and still allowing for further pedal travel on max braking, etc. Even at the base of the pedal this could amount to 1/2" of travel.

Perhaps they are a thing of the past and banned as being hazardous but they used to make switches that were opened/closed by a solution of mercury which could be mounted to a brake arm--this eliminated the problem of allowing for pedal travel, etc.

I don't mind dealing with inline hydraulic pressure switches on a street car but on race cars they are a problem because their failure mode is decreased sensitivity to slight pressures and it is easy to have them seem okay when one stands on them hard in the shop or at tech and yet not have any brake lights when doing light/moderate brake applications when racing. A reliable make/break (no pun intended) would be a real treat!

 

[dh100m]

mount micro switch normally open in a way that that as soon as the pedal is push it goes to close most switch have n/c n/o connections then the
throw dose not matter

 

[Michael Oritt]

I googled "Mercury Switch" and found this:

"Mercury switches were used in automobiles for lighting controls (for example, trunk lid lights), ride control, and anti-lock braking systems. Scrapped automobiles can leak mercury to the environment if these switches are not properly removed. These uses have been discontinued in new American-built cars since 2003."

I guess I am off to the scrap yard, or I could try something like this:

https://www.newark.com/durakool/a1b-003/tilt-switch/dp/46M4086

 

[steveg]

mercury tilt switches are still available on eBay and elsewhere:

 

[vette]

Michael, I might be very wrong but I don't know that tilt switches where used on brake lights. Do you want this switch to turn on the brake lights when you apply the brakes or are you looking for something that will turn on the brake lights just because the attitude of the car changes. Ya know, in my original post I mentioned using a spring. With a stiff spring on a pull switch the first application of pedal no matter how lightly will pull the plunger, with increased pressure and also increased travel of the pedal the plunger is already out and the spring just expands. I'm thinking that a tilt switch could very easily turn the lights on when you don't intend to have them on.

 

[John Turney]

Why not use a normally closed switch where when the pedal is "up", the switch is in contact with the pedal and opens the switch? Mount the switch so it is between you and the pedal. When the pedal is pushed, the switch closes and loses contact with the pedal until you let off of it.

 

[John Kuzman]

Michael -

Here is the switch I installed on both of my Healeys.

https://www.watsons-streetworks.com/switches/specialty-switches/the-best-brake-switch

 

[Michael Oritt]

John--

That switch is for a through-the-floor setup as is found in Healeys whereas my pedal is floor mounted. However it is possible that Watsons has another type or that the switch could be adapted. In any case thank you for the info.

 

[CessnaTPA]

Probably won't work in your application but here is the pic I promised. My brake lights are triggered with about a 1/4" of travel and I had to add a spring to flex to compensate for the lack of travel in my switch.

I would appreciate seeing them and/or getting info on where you got the switch. This is for one of my race cars, not for my Healey, and it has an organ-type brake pedal--that is, hinged on the floor as opposed to suspended.

 

[Michael Oritt]

Here's a somewhat primitive solution:

https://www.sw-em.com/brake_light_switch_rustic.jpg

 

[Keoke]

These uses have been discontinued in new American-built cars since 2003."

NAW:
They just call them Tilt Switches now---LOL

 

[RAC68]

Hi Michael,

You may have already made your choice of alternate brake switch but I thought I would indicate that I wired my new switch in parallel with my still-working original pressure switch rather then eliminate the original. At the time, I felt this approach would allow the new switch to be initially tested and adjusted with the original still functioning to as alternate unit until confident in the new installation. To validate this approach, for over more then a decade my alternate electric brake switch has been in place and obviously performing reliably with appropriate response ... to this point, only recent testing confirmed my originally-working pressure switch had stopped working during that period without being noticed.


When I installed my alternate electrical brake switch, I created a simple under-dash bracket attached to existing screws located on my heater plenum which allow the bracket to position my new brake switch button to play high on the brake peddle arm. When selecting my brake switch, I looked at a number of recommended switches and felt many to result in higher complexity then I felt appropriate or necessary and when roam around a near by salvage yard, collected a couple of Van brake switches (something I could not do today as salvage yards in NJ are as scarce as dinosaurs and none allow free roaming). The reason for choosing a brake switch from a Vans was that these often have a longer button and would be easier to position for riding on, and activated by the movement on the brake peddle arm.

Hope this helps,
Ray(64BJ8P1)

 

[MisterB]

Maybe some of the motorcycle type pull switches would do?

The spring allows for pedal travel after the contacts are engaged.
HTH
Mike

 

[3798j]

I don't mind dealing with inline hydraulic pressure switches on a street car but on race cars they are a problem because their failure mode is decreased sensitivity to slight pressures and it is easy to have them seem okay when one stands on them hard in the shop or at tech and yet not have any brake lights when doing light/moderate brake applications when racing.

If you can't come up with a suitable alternative, you might consider looking at what the hot rod/street rod community uses. Low pressure switches from Ron Francis. They activate on less than half the pressure of regular ones. I use one on a '55 resto-mod pickup. https://www.ronfrancis.com/prodinfo.asp?number=SW-32