manifold vacuum and brakes

I have always found that I have to press the brake pedal fairly hard on my CAV GT (#51). This is especially true on track days and the right leg gets a little tired. I today hooked up a vacuum gauge on to my holley 750 vac secondaries and found the reading to be 12mm Hg. Is this too low to operate the power brakes effectively?. Would a reserve vacuum canister help?.

 

[Johann]

If my memory recalls correctly, you need at least 18" HG at idle. (X 25.4 = 457.2 mm HG) for decent brake vacuum. (I stand corrected)

Don't you have a vacuum take off on the manifold?

 

[Randy V]

12" is pretty low to expect good consistent performance from your Power Brakes. Yes a reserve canister would be in order. There are also 12v powered Vacuum Pumps available for cars such as yours..

 

[Ian Clark]

Hi Syed, let me know how you make out on the diagnosis proceedure I sent. Cheers

 

[David Briggs]

Toss the brake booster, get a slightly smaller diameter Master Cylinder or better yet install a Tilton dual brake cylinder pedal assembly, as a bonus you will have lighter clutch action as the ratio on the clutch pedal is correct.
Dave

 

Thanks guys for all your advice. I will try to rule out a vacuum leak before doing any modifications to the braking system.