Product review (5 stars): Yay! it works
Have a Whirlpool Model WED5840SWO about 8 years old.
Symptom- drier would not turn on.
Checked the timer and it rattled and so replaced it as 'the internet' recommended.
Original was a 8566184 with no letter, this unit is a 'B'. Can see a few small differences but connections are identical.

Tools needed- needle nose pliers to remove wires from original, flat head screwdriver to help remove 220V connector.
Total time- less than five minutes to connect new unit, a couple more to close everything up.