Just broke in my trans am yesterday.. It started up fine, I didn't put in any shims, the engine turns over good still.. Today, after fixing my distributor, and a few other things, when going to start it back up to adjust the carb, it made a horrible grinding sound from the starter.. So, I figured it had to be shimmed, went to part source, and tested it out..
No luck, same noise.. Removed the starter, the bendix seems to be hung up, i put a flathead screwdriver in a slot where the starter gear is visible, and tried pushing it out, it comes out about.. 1/8" and won't go any more.. Could this be the problem?

I made sure to stop before I damaged the ring gear.

 

Any time you put a starter on a Chevy. You should check the starter alignment before you use it. You probably already damaged the starter. try this http://www.marinemechanic.com/site/page169.html

 

The starter looks more like figure two, with the end of the gear worn down.. I didn't try and start it while it was running though.