Originally Posted by northiam
11 inches of vaccum with standard pads
tha vacuum is your problem, i would say without looking at the vehicle. the booster to work at its best requires a text book 17-21" of vauum. does your booster hold vacuum when car is not running? is your one way valve working? with this amount of vacuum you will probably never get your car to lock up at all. you would be better off with drums on the rear as they dont require a booster they are self energizing.
my enginner is requiring me to run disc on the rear as well, i have explained to him this point when using a low vac engine. but the guidelines set out require this upgrade(downgrade) and it is not correct for the application intended.
you can use a vac tank to increase your booster storage, but this will not help it will only give a few more applications before recovery time. if you use one of these also make sure there is a one-way valve between tank and manifold port.