Advise on my car brakes?

i have a 1986 Chevrolet caprice 4 door 305 engine all stock on 24 inch rims. i have a slight problem. i noticed the other day when i had to brake very fast and hard that i pressed the brakes all the way to the floor (well as far as i could press them) yet the car seemed not to stop as fast as i thought it would. it has stock from dis brakes and drum in the back. i need some advice on either some simple tweaking or upgrading my brakes? i know the 24's do affect the stopping distance. what do you guys suggest? (and no im not trying get rid of the 24's)