Whirlpool washer stops at spin cycle

Machine runs wash cycle fine but when spin/drain cycle initiates the tub jerks and motor hums but the motor seems to be trying to overcome a load it can't and the thermal overload switch will trip if I leave it on in that part of the cycle. I have tried to manually start the drum rotation when spin cycle starts but it doesn't help even after I emptied the drum.
Does this have something to do with the basket drive or transmission system?
Thanks for your help
Larry