96 yukon rear tire locks up when apply brakes

I have a 1996 Gmc Yukon. My passenger side rear wheel locks up when apply brakes in dirt and wet roads. The brake pedal also seems to be soft. When I press the pedal it travels down aways and then it brakes very quickly and very jerky. I had Anti-lock brake light on but replaced the speed sensors and the light went away. Also have had a rear end brake job that didnt seem to fix the problem. Any help or suggestions would be greatly appreciated.

Thanks

Brake fluid on the shoes or a leaking rear axle seal will cause the wheel to lock up when the brakes are applied.

//2000CAYukon