Why does my engine shake and feel like it will slall when i brake?

Could be a few reasons but most likely a vacuum leak or the power brake booster

is defective... that is to say if you keep the car serviced... if not then it could be anything!!!!!!!!!!!!!!!

It could need a tune up, sparkplugs, distributor cap, rotor, and sparkplug wires. If it's old enough (1980) it could need a set of points !