you probably need to grease the caliper sliders, replace the pads, and get the rotors turned or replaced.

 

Right-o. There's a good reason for this too. It's a little off topic, but here's an experiment you can do yourself and you'll see exactly why the front brakes do most of the braking.

Find a long piece of wood, or something hard, and lean it up against a wall or on a pile of books to create a fairly decent slope. Get two toy cars (hot wheels work great), and some masking tape. On one car, tape the front wheels so they cannot spin, and on the other, tape the back wheels so they cannot spin. Let both cars run straight down the slope, and you'll see exactly why we use front brakes.