I think I'd noticed an inch of firewall flex. Besides, when you keep your foot on the brake pedal and turn on the engine- the pedal just falls away. It has to be the booster. I think 69hurstolds nailed it. There is no solid connection between the pedal pushrod and booster pushrod. The internal workings difference is the inch of travel. This whole argument began when a buddy suggested that with manual brakes- boosted brakes- or boosted with no boost- the pedal travel is the same. I showed him the yardstick difference yet he won't budge. In any other circumstance I would call him a moron and move on. But he inspects my cars and I don't want to alienate him. No matter how ignorant he can be.
Like I said, my explanation mode doesn't work all the time and words don't match what's in my head. Which is usually nothing new. I also acknowledge I am not an expert of the inner workings of the Delco dual diaphragm brake booster. I started looking up parts and stuff for it and the "balance" valve I was thinking of is simply called an "air valve". And the "control valve" is what regulates the atmospheric air coming in from the cabin, which goes through a felt filter around the pedal pushrod. If you hear a loud "whoosh" sound from the booster when it operates, check to see if the felt has degraded or fell out. It kinda acts like a noise filter too.
The m/c push rod, once it starts to move, will move the m/c pistons to stop the car with nominal difference in distance, which is what
TURNA was trying to describe. That's the "no" part of the travel distance. It's not really much of a difference in push rod travel at that point when the brakes are applied. But the booster guts have to move a certain distance and with the power assist, the movement is easier.
I guess the best way to explain the hard pedal you get when you run out of vacuum is that you're basically pushing the valve guts taking up the "slop" so to speak. THEN you start pushing on the m/c. So taking up the slack takes some pedal travel. So assuming you had the same length fulcrum between the manual or power brake systems, the "yes" part of the increased travel is including the part taking up the slop in the booster valving.
Is one better than the other? I prefer power brakes over manual brakes any day, although you always have to remember the more moving parts you add to a system, the more maintenance that system may need. Gigantic cams or boosted cars making plss poor vacuum makes manual brake systems more desirable due to that alone, but you can get vacuum cans, and other "tricks" to maintain your system with monster cam applications. Or get a hydroboost system, which comes with it's own set of problems. I don't know too much about that system except to me it acts like a mini brake system to assist your brake system.
In either case, manual or power assist, always make sure your brakes are adjusted properly and workings are top notch. You don't want a faulty brake system keeping you from celebrating your next birthday.
