76 Camaro Dirt Track Car... starter is (was) a rebuilt bigblock HD one,
that's been given a new nose to match the flywheel, and the gear
(bendix?) swapped for a used one when it jammed in the 307's bent
flexplate.

Was working fine. We had to pull the engine for oilpan repair (6 quart
circle track pan + inner tie rod grease fitting = hole.)

The car has three switches - power, ignition, and start. (makes it easy
to bump the starter without the ignition coming on.)

What started happening was the starter button appeared to jam on - spin
and spin and spin. Hitting the main power switch didn't kill it either.
Had to pull the battery cable. We did the "screwdriver" test across
the terminals with the main power off (only the big power wire is still
live straight from the battery) and it did the same thing - had to pull
the battery cable. Double checked all the wiring and the switch - same
thing.

We pulled the starter, and started dismantling it. Everything looked
ok, so we double checked the connections and bench tested it - ok...put
it back in the car, same thing.

the closest thing I could find in the shop manual taked about replacing
the "clutch" and showed the gear assembly which engages the flywheel as
being possibly bad, so we swapped it for one in a rebuild kit. That
appears to have fixed it, but I'm wondering if that was just dumb luck
or if that could actually have been the problem.

From what I can tell it's like the circuit that pulls the plunger and
everything "forward" when engaged was staying energized even when you
disconnected it (we have a quick connect on the firewall for pulling the
engine) and not disengaging.

The only "good" out of this is that I didn't discover this at the track.

Ray