Only enough for one good stop. 73 Duster

Trevor,

If you do a search on how power brakes work, you will see that all the booster does is assist. Which is why when you press slowly on the brakes all feels fine, but I suspect you are feeling what we all do with manual brakes. You should also know that the pedal to piston travel is generally less on manual brakes than on power assist brakes. This gives a greater mechanical advantage but longer throw with manual brakes. So required pedal pressure is less to achieve same stopping power. In your case you are likely not getting much assist because your vacuum may be too low. Generally you need at least 16 inches of vacuum at idle to generate assist. So your pedal to piston travel is likely less than a manual brake car, which means without assist it is harder to stop the car. You can check your brake pedal to see if there is a hole further from the pedal to connect the brake booster too and see how that effects the effort on braking. Keep in mind that the futher from the pedal you connect the booster, the longer your pedal travel will be. You can also try adding a vacuum canister. About $60 at Summit. Your engine is close on needed vaccum and the canister will see higher vacuum on deceleration as an example. The idea hear is that the canister accumulates vaccuum and holds it. Then when you hit the brakes there is sufficient vacuum to provide assist on repeat applicatons of brakes. Of course there is a limit and likely in heavy stop and go driving the benefit of the canister will drop off rapidly. This is where using an electric vacuum pump can help.

You also need to find out why your vacuum is as low as it is. If engine is stock it should be higher. You may have a vacuum leak. How does the engine idle? If it is rough and you hear some popping sounds at the exhaust, you have some engine issues.

I am considering going to vaccum assist brakes, but becasue of the cam in my 340 I will likely need a pump and canister. I am around 11 inches at idle. It is tough woeing this puppy down with manual disk/drum brakes.