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[jordanmills]

I think I figured it out. At least, what was wrong with mine.

The motor uses a basic brush motor. The brushes are carbon bricks, made to grind down as they keep contact with the (starter's) flywheel. The problem is that the casing doesn't allow this dust to drain well, and it gets caught up in the gear grease. This grease mixture gets all in the gears and makes things stick. It's not much of a problem in the summer, but when it gets cold the grease mix freezes.

This is really bad if it happens in the bendix gear. It seems to make the gear retract at a lower forward RPM. So the gear picks up the release of compression from the starting strokes and kicks back.

The solution, of course, was to rebuild the starter. I took it apart, washed it down (ajax works well, along with full immersion in ajax and water - note, do NOT immerse the flywheel or armature). I had to do a lot of scrubbing in hot water to get this nasty grease out.

Any way, I let it dry thoroughly, re-greased the gears and bearings, and put it back together. It's taking a few starts to get it back in order, but it gets better each time. I'm going to bet that I couldn't clean inside the bendix gear well, and that it's taking engine heat to work the gunk out. I think dropping it in a pot of boiling water for a few minutes would have helped a lot.

Any way, my truck is again starting almost reliably. And tonight my relpacement high torque starter from db electric came in. Oh well, now I have a mostly working spare.