'87 BII 2.9L FM146.

When I left work to go home Wed., I started the engine, engine ran fine, but the starter didn't disengage. Left the truck at work and came home, at Thanksgiving dinner, went back today. Same problem. Brought it home, took the starter out and discovered that I could slide the starter gear in/out by hand with almost no resistance. After a couple of test starts (starter still out of vehicle), The starter gear began sucking itself in and I could no longer slide the gear out by hand.

I'm looking for help understanding how the starter gear kicks out/sucks in, why it would not suck back in on its own, and (ultimately) whether or not I need a new starter.

 

When the starter is first connected to the battery current flows through a grounded feild coil actuating a movable pole shoe. The pole shoe is attached to the starter drive plunger lever and thus the drive is forced into engagment with the flywheel. When the movable pole shoe is fully seated it opens the field coil grounding the contacts and the starter is then in normal opertion. Normal field current and a shunt coil is used to maintain the movable pole shoe in the fully seated position during the time that the starter is cranking the engine.