How to remove and install an overrunning alternator pulley in 3 easy steps

The importance of overrunning alternator pulleys

Overrunning alternator pulleys (OAP) play vital roles inside accessory belt drive systems (ABDS). Every time the engine decelerates - for example during gear changing or engine shutdown - the alternator’s inertia creates resistance against the belt. OAPs allow alternators to “free-wheel” or “overrun” when the belt suddenly slows down. This prevents the belt from slipping and reduces vibration, wear and chirp noises.

As there is an OAP fitted in almost every recent car model, technicians need to be aware of the role and importance of the OAP, in order to maintain them properly as part of a drive system overhaul.

When to change alternator pulleys

A damaged overrunning alternator pulley cannot effectively dampen vibrations nor properly transmit power to the alternator; this can compromise the engine accessories, hence the importance of checking the overrunning alternator pulley at each service interval. It is also important to replace the overrunning alternator pulley when installing a new alternator. Specially adapted tools are required to remove and install an OAP. The Gates GAT4955A OAP tool kit contains a complete set of removal and installation tools.

The following guidelines will help you to remove and install an OAP in 3 easy steps. Note that these are general guidelines. Before attempting to install any OAP, always refer to the vehicle manufacturer’s recommended procedures for replacement and maintenance.

How to replace an alternator pulley in 3 easy steps


Make sure to use the appropriate tools: special tools are needed to remove and install an overrunning alternator pulley. Gates handy GAT4955A tool kit contains the complete set of required removal and installation tools.


Use the proper alternator pulley type for the specific vehicle: solid pulleys, one-way clutches and overrunning alternator decouplers are not interchangeable. So it is vital that the new alternator pulley is the same type of pulley that was installed by the vehicle manufacturer as original equipment.


Proceed with caution.
This type of installation requires the pulley shaft to be held with a calibrated torque wrench and the correct tool, the alternator rotor shaft is then rotated with a torque wrench (counter clockwise for right-hand threaded pulleys and clockwise for left-hand threaded pulleys).
Typically installation torque is 65 ft-lb/90 Nm unless otherwise specified.
In many cases it is possible to remove and install the overrunning alternator pulley while the alternator is still on the engine.

Special note when replacing overrunning alternator decouplers
The plastic protective cap cannot be re-used after it has been removed from the pulley. A replacement cap is supplied with the new part. Don't fit the new cap until you are absolutely sure the new pulley is fixed correctly. Some caps cannot be removed without damaging them after installation.

Inspecting for misalignment

Pulley misalignment is the most common cause of premature belt failure. Be sure to inspect your drive for misalignment and take corrective action.