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How to Know If the Alternator Bearings Are Bad

by Kelly Gray

An alternator on a vehicle keeps the battery charged while it is parked and while it is being driven. This is also where the power is generated to operate lights and other electronics inside the vehicle. The bearings are inside the alternator and are what the rotor rotates on to create the power. Many times, the bearings will squeak or make a grinding sound if they are going bad. If that is the case, it is likely that you will have to replace the alternator.

Feeling for Bad Bearings

Step 1

Turn off the engine and remove the key from the ignition. Never check the alternator bearings while the engine is running.

Step 2

Open the hood of the car. Locate the fan belt and remove it.

Step 3

Turn the alternator gently by hand. Reach down to feel the bearings as you turn the alternator. If you hear squeaks or sounds are heard or if the bearings feel rough as the alternator is turning, the bearings could be bad.

Push up and down on the fan. If the bearings are in good working order, the belt should not move.

Listening with a Tube

Step 1

Put the car in park and start the engine. Open the hood and locate the alternator.

Step 2

Cut a 12-inch piece of tubing. It doesn't matter what the diameter of tubing is, but a larger diameter will help you hear the sound better. Heater hose is also a good option.

Put one end of the hose near the alternator. Put the other end up to your ear. If the noise is louder near the alternator, it could indicate bad bearings.


  • Symptoms for a bad alternator are similar to those of a bad battery. Test the battery first before checking the alternator.

Items you will need

  • Tubing

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