Why won't my washing machine spin on its own?

Why won't my washing machine spin on its own?

My washing machine will agitate, drain, and sometimes spin. But most of the time, I have to open the lid and manually turn the tub to start the spinning process. Sometimes I have to do this several times before it will catch and start spinning on its own. My husband replaced the motor coupler, but that didn't solve the problem. What else could it be?

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