Why does my driver rear tire skid when I hit the.

What is the problem, the left wheel locks up too easily under light braking or the right wheel won't lock under heavy braking? If the left one locks too easily, suspect a left parking brake cable rusted in the partially-applied position or the axle seal is leaking gear lube onto the drum. If the right one doesn't apply hard enough, suspect the pistons are stuck in the wheel cylinder.