washing machine works intermittently?

Any ideas? My top loading washing machine keeps cutting off. It will run for 30 seconds and stop. after a few minutes it will start up and run for another 30 seconds and then stop. another couple minutes it will start run for 30 seconds and stop..........until a cycle is complete. I'm guessing that there is some sort of thermal protection on the motor that is doing its job. what could be causing this? worn brushes? control unit? Short? I did replace the timer with a new one and it seemed to fix it for a couple of days then it went back to doing the same thing. Thanks for your input.