How to check a used alternator before you buy it

A used alternator is one of the better value second-hand parts you can buy, but only if you know what you are looking at. Here is what our team checks before anything leaves the yard.

Spin the pulley by hand. It should turn smoothly in one direction and lock in the other if it is a one-way clutch pulley. Grinding, roughness or side-to-side play in the shaft means worn bearings, and a bearing failure will strand you just as surely as a dead alternator.

Look at the slip rings through the rear vents. Deep grooving means the brushes have worn in hard, which shortens whatever life is left. Light scoring is normal on any used unit.

Check the case for heat damage. Discolouration around the rectifier usually means the unit has been run hot, often because it was fighting a failing battery. That history matters more than the mileage on the donor car.

Finally, match the part number, not just the model. Two cars of the same year and badge can carry different output ratings depending on options. Send us your VIN and we will confirm it for you.