I have a question about the dual diaphram 7" brake booster. I know that a single diaphram produces so much pressure, but a dual will at least get close to almost double the pressure. So, when testing the dual system, how does one know whether both diaphrams are good and working? You can do the test, but if one diaphram is shot will the other be shot as well or will the unit still work because of one diaphram still working. I've pumped the pedal to remove the vacuum and then started the car. The pedal moved but not by a great amount. This is why I ask the question. My brakes are very hard to apply, especially when slowing down to make a right or left turn. I have a disc/drum setup, new residual valves and a proportioning valve. I talked to another street rodder with the same dual setup and he also indicated that his stopping power isn't what it should be. As a matter of fact, while towing his tear drop he had to make a panic stop but couldn't and plowed into the back of a motor home that stopped suddenly. He indicated that a panic stop (if he could) would have prevented the accident. Any light on this would be greatly appreciated.