TheSamba.com :: View topic - Using motorcycle brake light switch for quicker brake lights?

Tue Apr 29, 2025 2:28 am

It takes a lot of brake pedal pressure to activate the brake light switch!
I’m going to replace one of the switches on my dual master with one intended for a motorcycle. With the hopes the lights come on sooner, at a lower pressure, when applying the brakes.
My question is, which chamber of the master builds pressure quickest? Or, which builds the most pressure when brakes are first applied? Should I put the sensor in the “closest to the pedal” position or furthest away?

Tue Apr 29, 2025 5:18 am

If pressure is the issue then just mount a micro switch on the peddle cluster or on the firewall ahead of the brake peddle then you are working off motion instead of pressure.

Tue Apr 29, 2025 6:05 am

oprn wrote: If pressure is the issue then just mount a micro switch on the peddle cluster or on the firewall ahead of the brake peddle then you are working off motion instead of pressure.

That's our plan B. :)

Tue Apr 29, 2025 6:25 am

oprn wrote: If pressure is the issue then just mount a micro switch on the peddle cluster or on the firewall ahead of the brake peddle then you are working off motion instead of pressure.
If pressure is the issue then you've got an issue with your brake system !!!

Tue Apr 29, 2025 6:46 am

Fun With VDubs wrote: oprn wrote: If pressure is the issue then just mount a micro switch on the peddle cluster or on the firewall ahead of the brake peddle then you are working off motion instead of pressure.

That's our plan B. :)

Plan B should be plan A The switch on the pedal is superior, it can activate the stop lamps well before the master cylinder even begins to build pressure, it is very handy and safe. Many many modern car use this system.

This is a super upgrade, and is easy to implement

https://www.thesamba.com/vw/classifieds/detail.php?id=2140061

Tue Apr 29, 2025 7:33 am

You have a problem with your brake system.

Tue Apr 29, 2025 7:49 am

Let's clarify something. There is nothing wrong with our brake system. :lol:
ALL old Beetles that light the brake lights through pressure in the master have a slow response time and are far less sensitive to motion on the brake pedal compared to an electrical switch on the pedal itself. In other words, you have to press the pedal down further than with a pedal mounted switch to send current to the brake lights.

Yes, a switch on the pedal would probably be a superior way to go. But getting back to my question in my original post: :lol: :lol:
"My question is, which chamber of the master builds pressure quickest? Or, which builds the most pressure when brakes are first applied? Should I put the sensor in the “closest to the pedal” position or furthest away?"

Tue Apr 29, 2025 8:38 am

Fun With VDubs wrote: Let's clarify something. There is nothing wrong with our brake system. :lol:
ALL old Beetles that light the brake lights through pressure in the master have a slow response time and are far less sensitive to motion on the brake pedal compared to an electrical switch on the pedal itself. In other words, you have to press the pedal down further than with a pedal mounted switch to send current to the brake lights.

Yes, a switch on the pedal would probably be a superior way to go. But getting back to my question in my original post: :lol: :lol:
"My question is, which chamber of the master builds pressure quickest? Or, which builds the most pressure when brakes are first applied? Should I put the sensor in the “closest to the pedal” position or furthest away?"

High pressure is built as the shoes are pressed hard on the drums. This can be shoe to drum gap dependent in a dual circuit system. If your rear shoes are very close gap, and the front are very far gap, Id expect the rear circuit to see higher pressure first. And visa versa.
Likewise the flex in the rubber hoses can have an effect, old soft hoses on one circuit will give more stroke until higher pressure is built up Air in the lines or cylinder will also have an effect.

Why not install two lower pressure acting pressure switches? Then you are really covered, no matter which build up pressure first?

Also for faster light activation, LED lamps light up a good deal faster than incandescent lamps.

I run LED lamps and the linked switch for pedal movement, my stop lights turn on with about 1/8th inch movement of the pedal pad, I also installed high mount stop lamps (and turn lamps) in my rear window in the two lower corners.

Tue Apr 29, 2025 12:28 pm

zerotofifty wrote: Quote: Yes, a switch on the pedal would probably be a superior way to go. But getting back to my question in my original post: :lol: :lol:
"My question is, which chamber of the master builds pressure quickest? Or, which builds the most pressure when brakes are first applied? Should I put the sensor in the “closest to the pedal” position or furthest away?"

High pressure is built as the shoes are pressed hard on the drums. This can be shoe to drum gap dependent in a dual circuit system. If your rear shoes are very close gap, and the front are very far gap, Id expect the rear circuit to see higher pressure first. And visa versa.
Likewise the flex in the rubber hoses can have an effect, old soft hoses on one circuit will give more stroke until higher pressure is built up Air in the lines or cylinder will also have an effect.

Why not install two lower pressure acting pressure switches? Then you are really covered, no matter which build up pressure first?

Also for faster light activation, LED lamps light up a good deal faster than incandescent lamps.

I run LED lamps and the linked switch for pedal movement, my stop lights turn on with about 1/8th inch movement of the pedal pad, I also installed high mount stop lamps (and turn lamps) in my rear window in the two lower corners.

Thank you! That basically answers my question. One thing I neglected to mention is that I have discs in the front. What's your opinion on which of those will build pressure quickest, discs or drums?

Tue Apr 29, 2025 2:15 pm

In a dual circuit brake system, neither circuit will build working pressure faster than the other unless one of the circuits is failed. A brake being out of adjustment doesn't alter how soon a brake circuit builds pressure relative to the other, it only increases the distance the pedal must be moved before that happens. Doesn't matter if you have drums at all four corners, discs all around, or a mix of the two.

To answer "My question is, which chamber of the master builds pressure quickest? Or, which builds the most pressure when brakes are first applied? Should I put the sensor in the “closest to the pedal” position or furthest away?", the answers for the first two would be neither one in a properly functioning system, and the last would be it doesn't make a difference which you choose.

Wed Apr 30, 2025 2:12 am

mukluk wrote: In a dual circuit brake system, neither circuit will build working pressure faster than the other unless one of the circuits is failed. A brake being out of adjustment doesn't alter how soon a brake circuit builds pressure relative to the other, it only increases the distance the pedal must be moved before that happens. Doesn't matter if you have drums at all four corners, discs all around, or a mix of the two.

To answer "My question is, which chamber of the master builds pressure quickest? Or, which builds the most pressure when brakes are first applied? Should I put the sensor in the “closest to the pedal” position or furthest away?", the answers for the first two would be neither one in a properly functioning system, and the last would be it doesn't make a difference which you choose.

Thanks!!!

Thu May 01, 2025 11:38 am

Fun With VDubs wrote:
ALL old Beetles that light the brake lights through pressure in the master have a slow response time and are far less sensitive to motion on the brake pedal compared to an electrical switch on the pedal itself. In other words, you have to press the pedal down further than with a pedal mounted switch to send current to the brake lights.

It's not just old Beetles, newer Vanagons have the same problem. There's absolutely NOTHING wrong with the brake system other than the design requiring pressure to activate the brake lights. It's dumb: it delays activating the brake lights, it's a proven source of leaks, etc.

Using a brake pedal motion switch allows the driver to flash their brake lights w/out actually activating the brakes, even ever so slightly. Just like a modern car and it allows the driver to communicate to the text addled drivers behind them.

Thu May 01, 2025 2:25 pm

mukluk wrote: In a dual circuit brake system, neither circuit will build working pressure faster than the other unless one of the circuits is failed. A brake being out of adjustment doesn't alter how soon a brake circuit builds pressure relative to the other, it only increases the distance the pedal must be moved before that happens. Doesn't matter if you have drums at all four corners, discs all around, or a mix of the two.

To answer "My question is, which chamber of the master builds pressure quickest? Or, which builds the most pressure when brakes are first applied? Should I put the sensor in the “closest to the pedal” position or furthest away?", the answers for the first two would be neither one in a properly functioning system, and the last would be it doesn't make a difference which you choose.

Actually if one circuits brakes are way out of wack and the shoes dont touch the drum and the other not, one side may build pressure before the other. It is simply a matter if the volume required to build pressure on one of the other side exceeds or not exceeds the volume of fluid needed to activate the other side in the master.

Thu May 01, 2025 5:03 pm

zerotofifty wrote: Actually if one circuits brakes are way out of wack and the shoes dont touch the drum and the other not, one side may build pressure before the other. It is simply a matter if the volume required to build pressure on one of the other side exceeds or not exceeds the volume of fluid needed to activate the other side in the master.
Again, in a dual circuit brake system, neither circuit will build working pressure faster than the other unless one of the circuits is failed.

Situation 1, all brakes are properly adjusted. You push on the brake pedal and all shoes are quickly in contact with the drums. Pushing on the pedal past the initial point of contact builds equal working pressure in both circuits and all four brakes work.

Situation 2, the rear shoes are out of adjustment while the fronts are properly adjusted. You push the brake pedal and the front shoes are quickly in contact with the drums, rear shoes aren't there yet. Pushing the pedal farther, working pressure doesn't build in the front circuit because pedal movement is still moving the rear circuit piston/fluid/wheel cylinders to get the rear shoes in contact with the drums. You're getting a little concerned because you're having to push the pedal farther than normal. A little more into the pedal and the rear shoes are in contact with the drums, the pedal firms up, and pushing on the pedal past that point builds equal working pressure in both circuits and all four brakes work.

Situation 3, all brakes are out of adjustment, the rears are worse because "somebody" keeps driving around with the parking brake on. You push on the brake pedal and all shoes start heading toward the drums. It takes an increased amount of travel than before, but the fronts start to contact the drums. Pushing the pedal farther, working pressure doesn't build in the front circuit because pedal movement is still moving the rear circuit piston/fluid/wheel cylinders to get the rear shoes in contact with the drums. About the time you start to wonder if you're going to find out what the steering wheel or windshield taste like, the rear brake shoes come in contact with the drums and you finally feel the pedal firm up an inch away from the firewall. Pushing the pedal past this point results in working pressure building equally in both circuits and all the brakes work.

Situation 4, the rear shoes are horribly, hopelessly out of adjustment while the fronts are properly adjusted. You push the brake pedal and the front shoes are quickly in contact with the drums, rear shoes aren't even close. Pushing the pedal farther, working pressure doesn't build in the front circuit because pedal movement is still moving the rear circuit piston/fluid/wheel cylinders to get the rear shoes in contact with the drums. Unfortunately, the rears are so hopelessly out of adjustment that the rear circuit piston runs out of travel and its stop contacts the rear of the front circuit piston. Being now solidly in contact on through to the front circuit piston, pushing the pedal past this point will build working pressure in the front circuit only, and only the front brakes will work... hopefully well enough to stop before hitting the car in front of you. This is how you build differential pressure in the circuits and is effectively the same as having a failed brake circuit.

Thu May 01, 2025 6:58 pm

We can also look at this another way. Pascal's Principle applies here, as once the compensating ports in the master cylinder are blocked off by piston movement we are dealing with an incompressible fluid inside a closed container. The principle states "A change in pressure at any point in an enclosed incompressible fluid at rest is transmitted equally and undiminished to all points in all directions throughout the fluid, and the force due to the pressure acts at right angles to the enclosing walls."

The dual circuit system is essentially two closed containers, each with multiple pistons. Each wheel cylinder has two pistons, there are two wheel cylinders per circuit, and all are connected to the tandem master cylinder. Inside the master cylinder we have the rear circuit piston and the front circuit piston, each is capable of moving independently of the other (within certain travel constraints) as fluid moves into or out of the master cylinder.

The confines of the front circuit are the two front wheel cylinders and their pistons, the hoses and hard lines connecting the wheel cylinders to the front of the master cylinder, the interior walls of the master cylinder, and the front circuit piston.

The confines of the rear circuit are the two rear wheel cylinders and their pistons, the hoses and hard lines connecting the wheel cylinder to the rear of the master cylinder, the interior walls of the master cylinder, the rear circuit piston, and the rear of the front circuit piston. This last bit is important to note.

Since we know per Pascal's Principle that a change in pressure at any point is transmitted equally and undiminished to all points throughout the container, and we know that the front circuit piston is shared as a container confine by both the front and rear circuits, then we know without question that any change in pressure in one circuit will be transmitted equally to the other circuit. In other words, you cannot have a change in pressure in one circuit without also having the same/equal change in pressure in the other.

Thu May 01, 2025 8:54 pm

mukluk wrote: zerotofifty wrote: Actually if one circuits brakes are way out of wack and the shoes dont touch the drum and the other not, one side may build pressure before the other. It is simply a matter if the volume required to build pressure on one of the other side exceeds or not exceeds the volume of fluid needed to activate the other side in the master.
Again, in a dual circuit brake system, neither circuit will build working pressure faster than the other unless one of the circuits is failed.

Situation 1, all brakes are properly adjusted. You push on the brake pedal and all shoes are quickly in contact with the drums. Pushing on the pedal past the initial point of contact builds equal working pressure in both circuits and all four brakes work.

Situation 2, the rear shoes are out of adjustment while the fronts are properly adjusted. You push the brake pedal and the front shoes are quickly in contact with the drums, rear shoes aren't there yet. Pushing the pedal farther, working pressure doesn't build in the front circuit because pedal movement is still moving the rear circuit piston/fluid/wheel cylinders to get the rear shoes in contact with the drums. You're getting a little concerned because you're having to push the pedal farther than normal. A little more into the pedal and the rear shoes are in contact with the drums, the pedal firms up, and pushing on the pedal past that point builds equal working pressure in both circuits and all four brakes work.

Situation 3, all brakes are out of adjustment, the rears are worse because "somebody" keeps driving around with the parking brake on. You push on the brake pedal and all shoes start heading toward the drums. It takes an increased amount of travel than before, but the fronts start to contact the drums. Pushing the pedal farther, working pressure doesn't build in the front circuit because pedal movement is still moving the rear circuit piston/fluid/wheel cylinders to get the rear shoes in contact with the drums. About the time you start to wonder if you're going to find out what the steering wheel or windshield taste like, the rear brake shoes come in contact with the drums and you finally feel the pedal firm up an inch away from the firewall. Pushing the pedal past this point results in working pressure building equally in both circuits and all the brakes work.

Situation 4, the rear shoes are horribly, hopelessly out of adjustment while the fronts are properly adjusted. You push the brake pedal and the front shoes are quickly in contact with the drums, rear shoes aren't even close. Pushing the pedal farther, working pressure doesn't build in the front circuit because pedal movement is still moving the rear circuit piston/fluid/wheel cylinders to get the rear shoes in contact with the drums. Unfortunately, the rears are so hopelessly out of adjustment that the rear circuit piston runs out of travel and its stop contacts the rear of the front circuit piston. Being now solidly in contact on through to the front circuit piston, pushing the pedal past this point will build working pressure in the front circuit only, and only the front brakes will work... hopefully well enough to stop before hitting the car in front of you. This is how you build differential pressure in the circuits and is effectively the same as having a failed brake circuit.

Yeah, situation #4 is what I am thinking off, if there aint shoe to drum contact, pressure wont build in that circuit, but it may still build in the other after a certain amount of pedal travel.

Sat Jun 28, 2025 10:24 am

Does anyone know if there's a pedal-actuated brake switch for a '57 Oval pedal assembly?

https://www.thesamba.com/vw/classifieds/detail.php?id=2140061

Sat Jun 28, 2025 5:05 pm

Just go with a low pressure switch, I installed this one from good old amazon and it works very well.

https://a.co/d/cHvpP8C

Sat Jun 28, 2025 5:25 pm

liquidrush wrote: Just go with a low pressure switch, I installed this one from good old amazon and it works very well.

https://a.co/d/cHvpP8C

Are those threads compatible with VW MCs? What kind of electrical connections are those? They don't look like spade connections.
Appreciate the info.

Sat Jun 28, 2025 9:49 pm

Switches activate at ca. 50 psi, brakes operate at 500-2000 psi.

You guys are inventing a solution for a non-existent problem other that poorly serviced brakes