Top Load Washing Machine Wont Spin Effectively?

My Whirlpool top loading washing machine will attempt to spin, and does rather slowly but will not effectively wring out the clothes. This has been happening on and off for a couple months .. usually only when the load was improperly balanced. I would balance the clothes in the basket and respin, then it would work. Now it barely works at all on high spin and not at all on low spin.

Could this be something simple or do i have to call the repairman? Thanks!