I have a Sears riding mower 17 HP, 42" Model # 917/271661 that engages the blades fine but will not disengage the blades unless I cut the engine off. There is a spring that provides resistance when I move the lever on the dash to engage the blades; should there be another spring that pulls the blade pulley back away from the belt when I disengage the blades? I can't find one or where it would attach. The pulley just sits there when I release the lever up top.
With the motor turned off I can move the lever to engage the blades; then move the lever to disengage the blades.They don't disengage but if I pull just a little on the belt, the pulley moves to the disengaged position. Again this is with the engine off, but does it tell you anything?
And why will it disengage when the engine is turned off, but not when the engine is running?

Some of the Craftsman decks do have a return spring on top of the deck that goes from the moving pulley to a small hole in the top of the deck. It is close to the middle of the deck on top.

You can go to www.searspartsdirect.com and put your model number in there. You can see the breakdown of all of your parts including the deck.