The contacts in the solenoid were just a little rough. What carbon was there was merely a trace and cleaned up easily.

No, I wasn't trying different starters (I have learned I can use starters up to a 1984 240, though, and will eventually source one from a junkyard for $10)

Anyhow, I did try your ideas about attatching power to the varous terminals and that faston (blade) connection. I got the solenoid to click smartly, and the starter to spin happily. All this was bench testing.

In car, I attatched all the wires to the positive bolt, along with the heavy battery cable. The only connection not put there is the faston connection from the ignition switch (I believe it's from there)

So now, the symptom is just a loud click from one of the relays on the firewall, and the engine barely moves, resentfully, a fraction of a turn.

To eliminate the possibliity of a bad battery cable, I hooked the positive lead from my battery charger directly to the large positive bolt on the starter, but this didn't help any.

I have the starter on the bench again now, end cap of the solenoid unsoldered and pulled off. The copper contacts are only slightly rough. Nothing remarkable to be seen here.

So, now I'm scratching my head as to what to do next, as the solenoid does seem to be engaging the pinion because the motor does at least grunt an inch of movement.

BTW, I don't know what tight scew you mean about disassembling the starter (I did have the starter all apart anyhow) My brushh holder is held by the two long bolts which hold the case together. There is also a circlip on the shaft with spacers and washers. But that's all I remember. The only solitary bolt other that this is the one which holds the clutch fork in place, but that's at the pinion end of the unit.

The brushes were at least half good, and the commutator clean by the time I reassembled things.

If I put the unit back in the car, what would happen if I used jumper cables and touched the positive clamp to the bolt on the solenoid side of its switch, or, that faston (blade) connector?

Seems to me, if I dont't light myself up, the first option would tell my whether or not the solenoid contacts are good.

The second way would tell me if my ignition switch and wiring are good or not?

(I say this because the starter did spin happily on the bench when i touched this faston lead. If the starter should run strongly again, it would have to be the wiring or ignition switch, right?

And, yes, both ground straps are clean and tight.
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'Don't Understand Why People Abort Volvos, Either'