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My brake lights work, but I have to press firmly on the pedal, I don't suspect they're on when I'm just sitting at stop light with gentle pressure to keep my car from rolling. (53 Cavalier-Ultramatic)

I suspect I need to replace the brake light switch. I think I read somewhere that they can be problematic, or maybe this is just the way they were??? I know I can upgrade and put a mechanical switch under the dash, but I don't really want to.

In hindsight I should have replaced last summer when I rebuilt my Treadle Vac......

Thoughts?

On my ‘40, the switch comes directly off the end of the master cylinder, not angled off as in the photo. But someone with a ‘50s model knows btter

That's correct and is clearly shown here.

Not correct for V8's though: that switch is on the distro block for the driver front brake line.

https://packardinfo.com/xoops/html/modules/partslist/viewplate.php?cat=7&PlateNumber=42&partslist=1948-1954

The Napa SL134 is listed as the correct replacement in the parts x-ref but I seem to recall some having issues with leaks at the threads. Don't know if Napa had a bad batch or changed something but just be aware of that as a possibility if you try one.

Question - Are you using DOT-5 brake fluid?

If you are, be aware that brakelight switches are prone to failure when using DOT-5.

My brake light switch is perfectly fine.............when the car is running!

I was playing with my brake lights because I had changed housings, cleaned, polished, etc. I was checking all the lights after I put them back together, but without the car running, which of course makes a difference! I got it in my head that maybe the switch was failing, and started imagining someone running into the back of me because they didn't see my brake lights.

Oh boy, I think someone should take my keys away!

You brake lights should work regardless if the car running. They should be on a "always on" circuit vs a ignition/on circuit.

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And they do come on even when the car isn't running. What I was referring to is that when the car is running, and has vacuum, just a touch of the brake pedal and of course the brake lights come on, as opposed to when there is no vacuum and of course the brake pedal requires a firmer push. I think I was working on my car too late in the day.....

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It is amazing how much difference a few inches of vacuum does make. I did some very crude and unscientific tests years ago on a BTV's output pressure with and without vacuum.

Using round numbers, with 100 psi at pedal, no vacuum present gave approx 200 psi out of BTV. It is no wonder you really need to stand on the pedal if vacuum fails because 200 psi is barely adequate for a heavy car to even think about slowing down. Self energizing aspect of Bendix brakes when going forward explains how a low pressure can eventually bring the car to a stop. Very little effect from self energizing in reverse explains why it doesn't want to stop. A small driver even pulling on the wheel while pushing on the pedal would be lucky if they could even apply much more than 100 to pedal.

When vacuum was admitted and 100 psi was still applied at pedal resulted in approx 500 psi out of BTV and pedal pressure dropped so it registered only about 50 psi. Adding more pedal pressure to get applied pedal pressure back to 100 resulted in nearly 800 psi out of BTV.

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That's good information! When I get curious about something I do these "crude experiments" as well. Gotta know!

Just went through the debate about disconnecting the vacuum line when setting timing, some guys were saying you absolutely need to, and some saying nope, not necessary. The correct answer is that it is not necessary because our vacuum advance uses ported vacuum, not manifold vacuum. It's more important to make sure your engine idle speed is not too high and activating the mechanical advance. All this was confirmed by my experiments!