Bronco starter over heating-HELP!!!

I have a 1986 Ford that after I drive it around a little bit it I start to hear a grinding noise when I it is started. I thought it was maybe the starter was bad so replaced it. Kept on doing it, so replaced the flywheel. Still no fix. Shimmed the stater, replaced hot and nutrual wires, replaced sylonoid, and put a cover on the starter. Thougjht maybe the exhaust was making the starter hot and no that is not the propblem.

Once hot the start just free spins and I am lost as to what it could be. Flywheel is fine, stater tests good, and once it is cool starts fine.

Any suggestions?

351W
4x4

A starter that grinds and then free spins only once everything is hot, and works fine cold, usually is not getting enough voltage when hot, so the drive gear never fully meshes with the flywheel. Heat raises resistance in tired cables and connections, and a new starter will not cure that.

Measure it while the problem is happening, engine hot, with a helper cranking:

1. Meter across the starter itself: red lead on the starter's input stud, black lead on the starter case or engine block. Compare that with the voltage across the battery posts while cranking. A big difference means the loss is in the wiring.
2. Meter across the positive cable: one lead on the battery positive post (the post itself, not the clamp), the other on the starter stud. More than about half a volt while cranking means that cable or one of its connections, including the fender relay's terminals, is the problem.
3. Meter across the ground side: battery negative post to the engine block. Same half volt rule. A missing or corroded engine to frame ground strap is a common one.

If the voltages hold up when hot, go back to the mesh itself: pinion to ring gear depth (the shims you added go between the starter and the bellhousing, and too many or too few both cause grinding) and the teeth on the new flywheel or flexplate.

Our 1980 to 1986 Bronco wiring page has a starting circuit diagram (Fig. 11) showing the battery, fusible link, neutral safety switch, starter relay and starter, so you can see every connection in the path:
https://www.supermotors.net/reference/ford/bronco/1980-1986/wiring-diagrams

Dana