Alternator Pulley Coming Off While Driving

1. Faulty Alternator: It's possible that the alternators you purchased may have a manufacturing defect or are not compatible with your specific vehicle. It's crucial to ensure you are using the correct alternator for your DeVille. Double-check the part numbers and consult with a trusted automotive parts specialist to verify compatibility.
2. Belt Tension: Insufficient tension on the belt can cause the pulley to come off. It's important to ensure that the belt is properly tensioned and aligned according to the manufacturer's specifications. If the belt tensioner is worn or malfunctioning, it may need to be replaced.
3. Misalignment: Incorrect alignment between the pulleys and the belt can cause excessive stress and lead to pulley failure. Make sure all pulleys, including the alternator pulley, are properly aligned. If any pulleys are misaligned, they may need adjustment or replacement.
4. Seized or Damaged Pulley: As you mentioned, one of the parts driven by the belt may be seized or damaged. It could be a pulley, idler pulley, or another component. Carefully inspect all the pulleys and associated components for any signs of wear, damage, or restricted movement. Replace any faulty parts as necessary.

Considering the difficulty you're facing in finding a mechanic in your area willing to work on your car, it may be beneficial to seek out a specialized Cadillac or vintage car enthusiast community or forum. These communities often have experienced members who may be familiar with the specific issues related to your vehicle model and can offer advice or recommendations for mechanics who are knowledgeable about older Cadillacs.

Additionally, you can try expanding your search for mechanics outside your immediate area, considering those who have experience working on classic cars or specialize in older vehicle models.

Remember, diagnosing and repairing complex automotive issues can be challenging, so seeking assistance from a qualified and experienced mechanic is typically the best course of action. They will be able to provide accurate diagnostics and carry out the necessary repairs to resolve the problem with your alternator pulley.