ser. 70 spins very slow?

I have 4 kids, needless to say my washer is used EVERY DAY. I took a look while it was on spin cycle and the bottom thing (I don`y know the part name) is spinning as fast as it should be but the drum is spinning at 1/2 the speed or even less. I don`t know if it is belt or clutch driven either way something is slipping. If anyone knows the answer or even has an idea it would be very helpful.
Thanks Scott Girard
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