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Since it will kick out and spin with no load, doesn't that mean the parts inside the solinoid are fine? Or it's broke just enough to work without a load but not under one? Interesting. I'm with ya on it being the starter solinoid since I can't find anything else it could be. Once I can replace the starter, again I'll let you guys know if it works. I've tried 3 (2 donors) but maybe they were all bad too. Thanks to everyone having patients with me. I don't call myself a mechanic, but I can make things better than they were.Sure sounds like the solenoid on the starter is bad. I know you say it works during bench testing... but it isn't working under load.
GM has used this type of solenoid forever. There is a contact internally in the solenoid that connects the path for power to reach the armature brushes. They do this because you can't start spinning the gear before the gear is engaged on the flywheel/flexplate. So the first action of the solenoid is to drive the gear to the flywheel. Once there... contacts allow power to the armature.
Haven't heard of that before. It's just so odd that there's no other issues with this truck. If it's not the starter solenoid, I would think there's other things that would be wrong. As I said, I'm just going to replace the whole unit (again) and see if thet worksCould the "bendix" be pooched. On the old ford starters with an "over running clutch drive" the inside rollers or ramp can get screwed up so that it wont spin the flywheel even if its engaged.