Re: Power brake and standard trans.

Posted by PackardV8 On 2011/1/16 14:19:42

Yes, i deleted the post because i thot it no longer applied due to suddenly realizeing that we are talking about DUAL DIAPHragm boosters, not single diaphragm.

I'll add it back rite here:

Here's the way i think it works:

Engine vacuum is only used to exhaust or diminish the atmospheric pressure in the front 1/2 of the power unit. THus NORMAL atmosphereic pressure is doing all of the work on the pedal side of the power unit.

APROXIMATE conversion: 2 in hg of vacuum = 1 #/in**2.
SO 2 inches of vacuum = 1 psi of force.
i.e divide the vacuum gauge reading by 2 and that will yield the PSI force on the power unit.

Therefore: 15 in-hg of vacuum = 7 pounds/sq.in of force.
SO:
10" diaphragm = 3.14(5**2) = 78 sq inches x 7 psi = ~560 pounds of force OUT.
7" diaphragm = 3.14(3.5**2) = 38 x 7 psi = ~ 280 ponds out.

5.5" diaphragm = 3.14(2.7**2) = 24 x 7 = ~175 pounds out.