Vacuum advance brake

[cadcap2]

I am a brand new flathead ford owner. It’s always been classic motorcycles (Harley, Indian & BMW) and vintage airplanes ( pre 1967) but now it’s a ‘36 Phaeton with ‘12 volt, Pertronix, ‘39 brakes and engine, restored 30 yrs. ago and stored last seven. About finishing up the electronic ignition and can’t find a replacement vacuum advance brake piston. Need some advice / help locating a replacement vacuum brake piston. Also wondering if it’s really needed with today’s fuels?

Thanks much,
Chris

[Flathead Fever]

Most people say not to bother using it at all with modern octane. Just back it off all the way and if it doesn't ping don't worry about it, or they are replacing the end of it. Somebody will tell us what they are using on the end of the piston. You want the advance to come on as fast as it can without pinging. I don't have any personal experience with it yet but that is what I plan to do. It's not like it's one of your vintage airplanes so if it the experiment doesn't work out it's not such a big deal.

By the way, I'm jealous, I have wanted a vintage airplane ( 1930s biplane) all of my life and a 1947 Indian Chief. I already like you.

[Bill OH]

I backed the vacuum brake full off on my 38 distributor and I have done that as early as 1950 - top speed increased 12 mph. I think you will need to plug the vacuum port or line because if you remove the piston, the you have a vacuum leak in @5 cylinder, You should be able to find and install the piston, but leave it backed off, which in effect plugs off the vacuum to #5 cylinder.

[ford38v8]

I agree with most of the above, but with one caveat: The advance disc must have a minimum amount of dampening action applied to prevent erratic advance/retard bouncing. This requires only a gentle scrubbing by a freshly oiled piston leather, which itself may be cut from the tongue of an old leather shoe.

[flatjack9]

When vacuum is present, the brake is fully pulled away from the plate, so no damping action. If your plate wobbles, there is wear and should be fixed.

[ford38v8]

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Originally Posted by flatjack9

When vacuum is present, the brake is fully pulled away from the plate, so no damping action. If your plate wobbles, there is wear and should be fixed.

I didn't say wobble, I said bounce between advance and retard. Big difference.

[cadcap2]

Thanks much! I get the idea...just enough tension on the advance disk to let it go full advance with just a bit of friction on the disc to keep it from "bouncing" too much back n forth. I've got some thick leather...makin a replacement friction tip and then better than new!