Re: Treadle Vac Conversion

Posted by JeromeSolberg On 2022/2/1 21:50:29

Hi,

If it works it is very interesting, at the very least.

I have one observation, and a couple of suggestions.

Looking at the picture of the linkage:

Unless there is something I am not seeing, the pedal ratio would be the ratio of the distance from the pedal to the pivot, divided by the ratio of the distance from the booster axis to the pivot, measured perpendicular to the pivot axis. So looking at that picture and eyeballing it, I don't see anything more than 2:1. Could even be less. They seemed to go to a lot of trouble to make the pedal lever longer, but in the process moved the pivot away from the booster axis as well. Maybe i am just looking at it from the wrong angle.

I would suggest before you go this route you should:

A) Verify how the pedal ratio is calculated and what it actually measures out to.

B) Verify the master cylinder diameter they are using.

That way you can compare to what you would get with the original setup with an approximately 5/8" master cylinder diameter and a 1:1 pedal ratio.

Note - I have never measured the actual diameter of the T.V. piston (really a rod displacing fluid) myself, I have seen it as either 0.655 or 0.625 or even 0.62.

Pressure/pound of foot force =

4 X P.R. / 3.14159 / D^2

P.R. = pedal ratio
D = master cylinder diameter

So for:

D = 5/8 and a P.R.=1, you have

Pressure/pound of foot force ~ 3.25

for:

D = 1 and a P.R. of 4 you have

Pressure/pound of foot force ~ 5.09

for:
D = 1 and a P.R. of 3 you have

Pressure/pound of foot force ~ 3.82

for:
D = 1 and a P.R. of 2 you have

Pressure/pound of foot force ~ 2.55

Personally, I tried a 1:1 pedal and a Ford Courier dual master system with a small booster that fit just where the TV does, so like 7" diameter. It had a 3/4" cylinder diameter. So

for D = 3/4 and a P.R. of 1 you have

Pressure/pound of foot force ~ 2.37

it was NOT ENOUGH.

Now in the system above, it looks like they moved the booster over so they could fit a bigger booster in there, which would give you more boost/assist than the T.V., so perhaps you would have better or adequate brakes as long as you had vacuum. But if you lost vacuum - not a fun time.

Hope this helps!