I would make sure you have the correct starter motor, they have many different variations, next the starter shouldn't need shims, I would get a high-quality starter and like joe says inspect the flexplace teeth. Here is a generic guide and the instructions for your car in the images below:
https://www.2carpros.com/articles/how-to-replace-a-starter-motor
A clashing or grinding condition may exist due to improper engagement of the starter to flexplate on some 1987-88 models equipped with 4.3L/V6-262, 5.0L/V8-305 and 5.7L/V8-350 engines with automatic transmission.
To correct this condition, replace the starter drive assembly, with new drive assembly P/N 10456422, which utilizes a stiffer jump spring allowing for proper engagement. During starter drive assembly replacement, all ring gear teeth should be inspected. If three or more consecutive teeth are damaged, the flexplate should be replaced. Use flexplate No. 10128414.
1. Disconnect battery ground cable.
2. Raise and support vehicle.
3. Remove starter to engine brace and heat shields, if equipped.
4. Remove starter mounting bolts and lower starter.
5. Disconnect wires from solenoids, then remove starter from vehicle.
6. Reverse procedure to install.
Here is the part number of the starter you need.
ACDelco part number 337-1022
Please upload videos in your response to the problem so we can see what's going on.
Tuesday, April 16th, 2024 AT 8:46 PM