The Stovebolt Site Forums The Shop Area The Electrical Bay Starter troubleshooting advice needed

I am trying to troubleshoot a problem with starting my vehicle. I have a '48 Fleetmaster with a 6 volt electrical system and 216 stovebolt. The starter is a Delco Remy 1107009. When depressing the starter button on the floor, there is a bit of a grunt but the starter does not engage with much more than that. It tries but does not have enough power to turn the flywheel. Here are the things I have done so far:

Battery is freshly charged and putting out appropriate power.

Battery cables and connections are tight and without corrosion. Removed cables at both ends and re-seated and torqued them down.

Confirmed that motor is not seized by rotating the main shaft via fanbelt. Turned without difficulty and provided appropriate resistance for a normal engine.

Confirmed that starter motor rotates freely.

Depressed the starter button on the starter thus supplying power to the starter motor without engaging the drive gear to the flywheel. The power was sufficient to rotate the starter without a mechanical load.

The bottom line is that the starter appears to work without a load but does not have enough umph to turn the flywheel. Could this be a function of worn or missing brushes or something else failed on the inside?

So my initial thought here is that there is something wrong with the starter. Is there anything else I should check before popping for a rebuild? Am I even on the right track? Any advice is most welcome.