I have a 86 Monte Carlo SS replaced all brake parts including the line, the brakes work good for a year or so but now the brakes are hard again,I can't even do a burnou(but after driving the car awhile I can do a burnout) the car tries to go forward when I'm on the brakes and the gas ,before driving it for awhile, I just put a vacuum can on it and the brakes are still hard and how much vacuum does a car suppose to have, and also I have a single booster is a dual booster bettr? 
