2001 Cavalier 2.2 5-speed manual 255K.

Have had starter / starting issues off and on for years. Same problem, multiple mechanics, lots of money, a bunch of different starters, nobody was ever able to explain anything - have heard it all from just bad luck with getting bad starters, to faulty recall work on the starter relay harness and/or relay, etc.......

Well after not having the problem for 5 years from May of 2015 to February of 2020 - it came back. Loud screeching, grinding noise with totally intermittent starts. Starter always activates when I turn the key but doesn't always start. It sounds like it either doesn't engage the flywheel or barely engages the flywheel and slips off (I have no idea if that is what is happening but it is why I am asking this), Anyway back in February, I knew that this time I was going to try and solve this problem myself and buy and install a new starter myself since every place I have taken it had no clue and ended up wanting to put a new starter in anyway even though that hasn't fixed the problem (for long).

Well it turns out that so many other disasters and problems have happened in the last 3 months, that I have been starting the car all this time with the same loud horrifying noise and same problem. Sometimes it starts right up like a new car, and other times, it takes 20 attempts and gets everyone's attention fort a square mile because of how lout and awful the noise is.

So my question is - could it be a shimming issue? And if so, can someone explain how this could be with so many different starters over the years. What would make a starter that had been working fine for 5 years suddenly need a shim? I am worried that if I put this new starter in, it wont fix the problem. I also don't understand how to measure for whether the shim is the issue or not - because it is impossible to get into the bendix gear area once this thing is bolted in because it is inside a half-dome metal protective shield.

If anyone knows what I am talking about then feel free to enlighten me. Do Cavaliers like mine require shims? I see that there are 2 types of shims too - the ones that move it further away from the transmission (downward), and the ones that move it laterally further out away from the flywheel to the side). How do I know which of those would be causing my problem or if this has anything to do with my problem at all? I initially was sure it was a relay problem but this starter has worked all these months consistently as far as the solenoid goes. So maybe it is a shimming problem.

It sounds like you need to have a look at your flywheel ring gear.
Take out the starter and using a screwdriver or similar, rotate the flywheel a bit at a time until you have physically SEEN all of them.
I suspect you have some damaged teeth.

Steve