When I press my brake pedal my rear wheels slide when I try to stop.

What is your question?

Had rear brakes adjusted stopped normally for a few days and problem started again. Mechanic told me to buy new drums, brakes shoes, wheel clylinders and brake hose. Had these items installed and a few days later problem started again. This is a 1984 Ford F-150 302 5.0 liter engine 2 wheel drive. Please help?