How to Replace a Pulley Bearing on Alternator


Replacing a pulley bearing on 90 percent of alternators is a fairly benign task, the hardest part typically being the removal of the alternator. Some vehicles feature the alternator on top of the engine, and hence relatively easy to remove. On other models, the alternator is on the bottom of the pulley system for the drive belt, in which case you must lift the vehicle. A Haynes repair manual for your specific vehicle will guide you through the alternator-removal process. In many applications, to replace the pulley will require the removal of the alternator.

Things You'll Need

  • 1/2-inch pneumatic impact gun
  • 1/2-inch drive impact socket set
  • Channel locks
  • Replacement pulley bearing
  • Torque specifications for the pulley bearing
  • Torque wrench
  • Place a suitable sized 1/2-inch drive impact socket onto the alternator pulley bearing retaining nut.

  • Test the gun to make sure it is rotating counterclockwise.

  • Attach the anvil of the gun to the square drive of the socket.

  • Use a pair of channel locks to hold the pulley bearing stationary.

  • Remove the pulley bearing.

  • Insert the new pulley bearing in the alternator. Replace the washer and the pulley bearing retaining nut. Hand-thread the nut on.

  • Snug the nut with the impact gun, but do not over-tighten it. Tighten the pulley bearing retaining nut to the correct torque specifications for the specific alternator you're working on.

Tips & Warnings

  • Be sure that your replacement is the same size and kind of pulley bearing as the original. Altering pulley sizes can cause the ratio of the crank and pulley bearing to become out of sync, drawing too much power from the alternator or not enough.
  • Be sure that the alternator doesn't call for an overrunning alternator decoupler (OAD) pulley. If so, replace it with one. Many new vehicles use OAD pulleys because of their superior performance over a conventional pulley. Replacing a regular pulley on an alternator that uses an OAD pulley can cause severe vibration in the drive belt and damage other pulleys.

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