Home Maintenance: Washing Machine (from the archives)

If the machine is rocking or vibrating excessively during the spin cycle, it may be unbalanced. To fix this, stop the cycle, open the lid, and redistribute the clothes evenly around the agitator. Close the lid and restart the spin cycle. But if the problem persists, check that the washer is level and adjust the feet as necessary.
As I discovered recently, if the machine is bouncing excessively, and the above steps don't help, check the shock absorbers. These can wear out over time, especially if the washer is frequently overloaded. Replacing the shock absorbers is a more involved repair, but still something a moderately handy person can do.