How to Replace an Alternator Pulley

Written by chris stevenson
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How to Replace an Alternator Pulley
It takes a few special techniques to remove the alternator pulley. (Hemera Technologies/ Images)

All vehicles have alternators. Alternators produce electricity by using a rotating pulley, driven by a single belt or serpentine belt. The rotation of the pulley spins a shaft connected to an armature and brushes inside the alternator housing. Sometimes, the pulley suffers impact or wears on the key way shaft, setting up an out-of-balance wobble. As a result, the pulley can break, or wear the belt prematurely or throw it off the pulley grooves. Replacing the alternator pulley requires a few steps and special tools, but any vehicle owner who wishes to tackle the job can perform the task.

Skill level:

Things you need

  • Owner's manual
  • Bench vice (wide-jaw)
  • Socket set
  • Box-end wrenches (six-point)
  • Hammer
  • Rags
  • Wood blocks
  • Penetrating oil
  • Air ratchet (if applicable)

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  1. 1

    Place the vehicle in park or neutral with the emergency brake set. Raise the hood and disconnect the negative battery cable at its post. Consult your owner's manual for the location and mounting bolts for your alternator. You will have a serpentine belt system or a single alternator belt configuration.

  2. 2

    Locate the back of the alternator case. At least three wires need to be removed -- one large battery (BAT) wire and two smaller ones. Make a note of which wire goes to what terminal. Use a small box-end wrench or a small socket to remove the nuts and pull the eyelet wires off. Push them out of the way.

  3. 3

    Find the adjusting bolt on the alternator. It will usually be on the top of the alternator, connected to a slotted support arm. Loosen the adjusting bolt and slide the alternator along the arm so it slacks enough to pull the belt off. Set the belt aside.

  4. 4

    Find the belt pulley tensioner and place a socket on its centre-mounted hex nut (if you have to remove a serpentine belt). Your owner's manual will show the location of the pulley tensioner. It has a flexible pulley arm that holds the belt tight. Twist the socket counterclockwise, enough to unload the spring pressure on the belt, then slide the belt off. Important: for serpentine belts, make a diagram of the belt routing configuration, so you can install the belt back in the position.

  5. 5

    Locate the alternator main mounting bolts and nuts. Most alternators have a long shaft bolt with a nut on the end. Use the correct socket to loosen it and pull the mounting bolt completely out. Set the bolt and nut aside. Take the alternator to a workbench equipped with a large-jaw vice. Soak the alternator pulley bolt with penetrating oil and let sit for 15 minutes.

  6. 6

    Wrap the pulley in several rags and place it edge-on in the vice. The vice jaws should grip the pulley only, not the cooling fins. Prop the weight of the alternator up with some old books or wood blocks. Place a box-end, six-point wrench on the alternator pulley bolt and turn it counterclockwise. Strike the wrench with stout taps of a hammer if it proves to be stubborn. Pull the pulley straight out on its key way shaft.

  7. 7

    Take the alternator to a tire shop, if the pulley refuses to come off. They will use an air ratchet to shock the mounting nut loose. Pull or use a hammer to tap the pulley off the alternator shaft. Do not lose the small metal guide key.

Tips and warnings

  • Do not wedge any tool in the pulley fins to stabilise it for removal. You could break them.

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