* Flywheel/Flexplate Damage: The most likely culprit is damage to the teeth on the flywheel (for a manual transmission) or flexplate (for an automatic). The new starter might be engaging with a bent, broken, or worn tooth, causing the grinding. Inspection is crucial. You'll need to visually examine the flywheel/flexplate for damage.
* Starter Mounting Bolts: Even with shims, the starter might not be perfectly aligned. Check that all starter mounting bolts are tight and that the starter is securely seated in its mounting bracket. A slightly loose or misaligned starter can cause grinding.
* Incorrect Starter: Though less likely after a new installation, double-check that you installed the correct starter for your specific vehicle. A slightly incorrect starter can lead to engagement issues.
* Engine Block/Transmission Misalignment: In rare cases, the engine or transmission itself might be slightly out of alignment. This is less common but could contribute to the problem, especially if there's been recent engine work. This is a more complex issue to diagnose.
* Starter Drive Gear: Although you have a new starter, there's a small chance the starter drive gear itself is faulty or slightly damaged. This could cause inconsistent engagement.
Troubleshooting Steps:
1. Visual Inspection: This is the most important step. Remove the starter (carefully!) and thoroughly inspect the flywheel/flexplate teeth for damage, wear, or bending. Look for any signs of impact or debris.
2. Check Starter Mounting: Ensure all the starter mounting bolts are tightened correctly and that the starter sits flush against the engine block.
3. Re-check Shims (and their placement): Make absolutely certain the shims are correctly positioned and haven't shifted during installation. Incorrect shim placement can worsen alignment.
4. Professional Diagnosis: If you've checked all of the above and the grinding persists, it's time to seek professional help. A mechanic with experience in older vehicles can diagnose more complex issues like engine/transmission misalignment or a more subtle starter problem.
Remember safety first! Disconnect the battery negative terminal before working on any electrical components. If you're uncomfortable working on your vehicle yourself, don't hesitate to take it to a qualified mechanic. Ignoring a grinding starter can lead to more significant damage.
