85 Z28 starting problem

I have an 85 z28 305 4bbl automatic. It wont start when you grind the starter as you normally would. However, if you just bump the starter you can eventually get it to catch and start. Runs like a sewing
machine after that. You have to use this bump method anytime you start the car. It is getting gas. So far I have replaced the starter, alternator and rebuilt the distributor. Can anyone tell me what is going on?? Im stumped as is my father in law who has been a mechanic all his life.
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The first thing that comes to mind is a broken tooth, or a severely cracked flywheel. If it's not catching, that's an obvious potential problem. I once had a similar problem with a '78 Regal, and what it turned out to be in my case was a cracked flywheel. Somehow, the flywheel was cracked ALL AROUND...how it kept in place without completely disintegrating amazed everyone! With the crack all the way around the flywheel, the angle would change, pretty much at random, and pretty much just jammed the starter gear against the flywheel like it was in a vice, and it simply refused to turn over. End result was that we replaced the flywheel and fixed the non-starting problem.
Keep in mind that, even with the cover removed, you COULD BARELY SEE THE CRACK!!!
Another is that you might need to shim the starter, as it may be pressing too hard against the flywheel and not being allowed to spin freely, or simply not catching. You can shim the BACK of the starter if it's too far out, shim the FRONT of the starter if it's too tight to the flywheel. (You can also take the time while you've got the starter off to check the flywheel for damaged teeth, "semi-circular" cracks, or cracks around the bolts which can cause the same problem.)
Final idea is that it might just need a new cable to the starter. If it's not getting POWER, it's obviously not going to spin...although I've personally never seen this myself, I've heard it's possible.
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sintalio wrote:

Have you got an ignition feed while you are engaging the starter. You appear to have a feed once the key is released.
The old Mercedes had two feeds to the ignition using a high & low rated ballast, One for start, One for run.
I think my old '78 Camaro had just the one feed to the ignition though.
HTH
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sintalio wrote:

Have you got an ignition feed while you are engaging the starter. You appear to have a feed once the key is released.
The old Mercedes had two feeds to the ignition using a high & low rated ballast, One for start, One for run.
I think my old '78 Camaro had just the one feed to the ignition though.
HTH
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