Been having starter problems on my 80 vette. Had a new starter replaced about a month a go and now I am having problems with starting. Won't do it every time, But when I turn the key to start, I get a click(hesitation) before it will turn over. Do I need to shim the starter and if so, how do you determine how many shims are needed?

I doubt it's a shimming issue with the hesitation problem. Check your battery connections and grounds. To check for shim requirements, I would put some prussian blue on the starter gear and test it once or twice. Then remove it and see how the gears hit by the pattern left on the starter gear.

Checking the pattern is the best way to tell. There is a gauge you can get that will measure the starter gear to flywheel clearance. It's really nothing but a metal rod. It fits into the flywheel tooth grove, and lines up with the starter tooth at the top of the tooth. If it fits, the clearance is right.

Usually what ever shim the car had is what you put back. If it had none, use none. Granted this is only for inital adjustment. If it works there without grinding (tooloose) or whining or staying engauged (too tight) is okay.

But the spacing is not your problem. As stated, check for loose connections, battery voltage, and starter condition. Sometimes a new one can be bad.