Brake Vacuum Booster

[foxxinabox at wideopenwest.com (foxxinabox@wideopenwest.com)]

  currently my '85 is only getting about 23mpg and it's performance is
lackluster with the modifications made to it. i have noticed that the pedal
takes much more effort than my '86 to get the car to stop. i'm thinking that
the brake booster is hosed (hence severe vacuum lead), but is there anyway to
test? the bentley makes mention of testing and replacing but only gives
instructions on replacement. i also have a few boosters from cars i've parted
out. anyone know of a way to test those? just looking for information before i
go draining and rebleeding the brakes multiple times. thanx.