To be honest, I've never worked on the PTO of a 550. If it's like the Fleetlines  Supers or 880's, the shaft from the flywheel turns anytime the engine is running. That gives you &quot;live&quot; PTO. At the rear of the tractor there should be a large &quot;round&quot; cover where your PTO lever goes in. Inside that cover are the PTO clutches and a mechanism to take the PTO in and out of gear. I think that is the area you need to look at.

 I'll take a looks at my IT manual and see if it's got anything in there.