not draining

Hello
Have a problem with my Whirlpool washer Model LSR8433KQ0.
The agitator works and fresh water will come into the tube,
but when the timer moves to any “Rinse” position the dirty
water does not pump out and the spin cycle doesn’t happen.
There is a humming noise when the timer goes over the “Rinse”
position but nothing happens.
Removed the pump, motor, and checked the motor coupling.
Outside the unit the motor shaft turns easily and turns the pump shaft.
I can turn the rubber/plastic coupling still inside the machine with my hand
and it turns the agitator OK.
Your expertise for a repair solution is very much appreciated!
Regards
Bruce