Using motorcycle brake light switch for quicker brake lights?

[Fun With VDubs]

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?
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Swing on over to our YouTube channel. There we post work we're doing on our VWs, and the adventures we take them on.
@FunWithVDubs

[oprn]

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.
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Our cars get old, we get old but driving an old VW never gets old!

[Fun With VDubs]

[Cusser]

[zerotofifty]

[Q-Dog]

You have a problem with your brake system.
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Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[Fun With VDubs]

Let's clarify something. There is nothing wrong with our brake system.
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:
"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?"
_________________
Swing on over to our YouTube channel. There we post work we're doing on our VWs, and the adventures we take them on.
@FunWithVDubs

[zerotofifty]

[Fun With VDubs]

[mukluk]

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.
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1960 Ragtop w/Semaphores "Inga"

[Fun With VDubs]

[jimf909]

[zerotofifty]

[mukluk]

[mukluk]

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.

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1960 Ragtop w/Semaphores "Inga"

[zerotofifty]