OK...need help. I just don't get it. Dual M/C with a booster...then added a reservoir...with the cam in my 351C, I get one or two good stops then a hard pedal. So...I am adding a vacuum pump. Now - here's what I just don't get... The vacuum pump doesn't pump air out...it ****s air in...so From where in the hell is it ****ing air from? And then how does it fill a reservoir and the booster? And what is it filling it with? What am I missing here? Do I need some special gl***es to see it!?
It is not filling anything, it is emptying the air that is in the system out thus creating vacuum. When you push on the brake pedal you are letting air in on the other side of the booster diaphragm and that air pressure is helping you (***ist) in pushing the brake pedal down against the master cylinder. Normally there will be check valves in the vacuum side of the system that prevent the vacuum from leaking to the air pressure side of the system. So, think of it as the high pressure side (atmosphere or "air" at 14.7 psi) and low pressure side, the side that your pump has ****ed all the air out of it that it can. The difference between the two sides is what is pushing on the diaphragm inside the brake booster, you are letting atmospheric pressure into one side when you push on the brake pedal and acts against the vacuum that came from the intake manifold / vacuum pump combination (low pressure). At some preset point the vacuum pump will turn off because it has removed all the air it can remove from the reservoir / booster. When the pressure rises in that side of the system (low pressure side, you let air in by pushing the brake pedal) normally the manifold vacuum will remove enough air to create proper vacuum to make the brake booster work but if the cam is not letting the engine produce enough vacuum the pump kicks in to ***ist. Even cars with big cams make vacuum when decelerating with a closed throttle, if everything is plumbed correctly with check valves you should never run out of vacuum while driving.
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