Overrunning alternator pulleys (OAP) are the key element for less wear to the accessory belt drive system. They take away much of the abuse in the system. Failure of the pulley, wear and tear on the inner spring and malfunction of the overrunning clutch mechanism can occur. A damaged overrunning alternator pulley cannot effectively dampen vibrations nor properly transmit power to the alternator.
Replace the overrunning alternator pulley when servicing the accessory belt drive system

Gates recommends:
  • check the overrunning alternator pulley when replacing any accessory belt drive component and replace if necessary;
  • replace the overrunning alternator pulley at the vehicle mileage or age specified by the manufacturer;
  • always replace the overrunning alternator pulley when you install a new alternator;
  • replace the belt, the tensioner and the OAP at the same time.
If one of these two tests fails, the overrunning alternator pulley must be replaced immediately!
  • Test 1: Use your index finger and your thumb to hold the inner ring (shaft) in place. Rotate the outer ring with your other hand in the same direction as the belt would. If the outer ring moves, you have to replace the OAP.
  • Test 2: Hold the inner ring (shaft) so it cannot move. Rotate the outer ring in the opposite direction of the belt. You will probably feel a little resistance, but the outer ring should rotate smoothly. If it does not, replace the OAP.
  • Note: OAD's will have a spring feel in the drive direction and should rotate smoothly in the opposite direction. If not, replace the part immediately. The internal spring is strong and may require a wrench and special tool to properly diagnose the pulley.

Overrunning Alternator Pulley toolkit GAT4955A

Specially adapted tools are required to remove and install the overrunning alternator pulley. Gates offers you the GAT4955A tool kit, containing a complete set of OAP installation and removal tools.

Illustration of the overrunning function of an OAP.

Watch how the torsional vibrations in the drive are being absorbed.

Watch the difference in performance of the drive.

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