pentair dynamo pump issues

hello new to the forum and looking for advice on my dynamo pump. My pump wouldn't start Monday evening after back washing, it just hummed. The motor is a 1.5 hp without a capacitor. On the bench, I can get the motor running with the impeller off and by turning the shaft a little to help it get going. Whenever I put the impeller back on it screws too tight against the diffuser and rubs, stopping the motor. I am wondering if this would be the seal worn down too much, the front bearing, or the impeller itself. Everything seems to be very clean and in good repair, just cant figure why the impeller tightens down too much.
Thanx in advance for any help

. . . membership updated.

I can't help with your question; I've never disassembled that particular pump, nor have I encountered a problem like that on any other pump.