Alternator Clutch Pulley Symptoms: Diagnosed and resolved overrunning alternator pulley

A noisy engine, problematic battery, and having issues with the car startup, all these problems can be the indicator that your alternator clutch pulley is probably not in good shape. While sometimes, there cannot be any alternative but changing the alternator pulley, it can be fixed by following simple steps even by yourself, if you are lucky.

Today we are going to look deeper into some common alternator pulley problems and some possible ways to fix them.

Schematic of one-way clutch alternator pulley source:

Bad alternator clutch pulley symptoms

If you notice too much noise in the engine that lasts for 1 to 5 seconds after shutting it down then it is most probably the alternator clutch pulley that is at fault. The very first sign of a worn out overrunning alternator pulley is the excessive tensioner movement that is the main cause of this sound.

A short chirping sound during the startup or shutdown of the engine is the first symptom of a bad alternator clutch pulley.

How to fix Alternator pulley not spinning?

The unspinning alternator or a seized alternator causes various problems to the engine. It sometimes agitates the owner and the first thing that comes to mind is to replace the seized alternator pulley. But knowing the correct way of fixing an alternator pulley will solve the problem as well as save that money as an alternator pulley in the market can cost up to $200.

To fix a seized alternator pulley it is not even necessary to take it out of the car and it is very simple to fix it at home.

The alternator is around the stator and not the bearing, put in a little bit of motor oil or some transmission fluid, wait for it to soak it in. Now put a socket with a breaker bar on and work it back and forth.

If the alternator is on the car squirt oil into the alternator, you can also spray quite a bit of oil in because the oil will not damage the windings, here old motor oil can also be used.

The seized up alternator can also burn off the belt completely, if the engine is turned over with the seized alternator it can create smoke and squealing. Now put a socket in the breaker bar and move the seized pulley, the first movement can get a little tricky but once it is done it will become as smooth as a brand new one.

If the belt is burnt, change the belt and everything will get just like new again.

How to fix alternator pulley loose?

There are two ways to fix a loose alternator pulley, here we are going to discuss both briefly:

  • You can tighten the pulling nut with a 15/16 pass through socket, using a torque wrench with a 5/16 hex head socket secure the pulley nut so it does not move. The rotor shaft has to be tightened to 95 to 108 N-m or 70 to 80 lb. ft.
  •  In the hexagonal hole at the end of the rotor shaft place a 5/16 hex wrench to hold. Now use a click-type torque wrench with an open ended 15/16 wrench tighten pulley nut to 95 to 108 N-m or 70 to 80 lb. ft. Make sure to tighten the pulley properly if not done right the pulley will loosen over time.

What is alternator overrun pulley?

The alternator overrun pulley or one way clutch turns only one way clockwise or anticlockwise and the other way is locked. It allows the alternator to free turn when the engine slows down or decelerates and decouples that mass away from the engine so it is not creating any vibration in the belt drive system.

What is the purpose of a clutch pulley on an alternator?

The clutch pulley on an alternator allows the belt to turn freely in its own speed in one direction when the engine suddenly slows down.

VW alternator pulley noise:

A properly functioning overrunning alternator pulley results in a smooth and quick running accessory belt system. Whereas when the overrunning alternator pulley fails it starts to make lots of flapping and chattering accessory belt noise that comes from the front side of the engine when the engine is running.

Alternator clutch pulley price:

One has to keep all the internal parts of the car working at a high level in order to obtain the best experience of the vehicle. Even the slightest problem in one of these parts can affect the engine directly. Also if one of the parts gets into trouble its replacement cost can become quite expensive.

The price of an alternator clutch pulley depends on the severity of the problem, if the car is in inspection regularly and the problem is a spot in time the cost will not be as much as the fully bad alternator.

The total cost of replacing an alternator clutch pulley ranges from $80 to $200. With that labour cost will be added depending on the specific auto body shop and its hourly labour cost.

How to remove alternator clutch pulley?

First you need to wear a heavy glove to get started with the task, it is important to take safety measures like wearing gloves and eyewear. If the alternator has external fans it can spin while removing and you may hurt yourself. Now if the pulley nut has the standard right hand threads rotate in an anticlockwise direction for removal if not then rotate clockwise with a ½ drive impact wrench or 15/16 socket while keeping your eyes at the alternator.

How to replace alternator clutch pulley?

Alternator pulley replacement can be started after removing it successfully following the steps mentioned above. Now for the alternator pulley replacement take a new pulley and they usually slip fits perfectly but sometimes thread locking fluid or rust gets between the shafts. In this case a slight amount of heat or puller is needed to remove the pulley. Remember not to overheat. Now, install the new pulley, lock washer and nut then secure by hand. Do not overtighten the nut.

How to check alternator clutch pulley?

To check the alternator clutch pulley first remove the plastic cap. Stop the alternator from rotating and then try to spin the pulley over the alternator. If it is okay it will freely spin one way and it won’t move backwards.

Why do alternators have a clutch pulley?

Overrunning alternator pulley or OAP simply works as a one way clutch mechanism that has been incorporated into the alternative pulley. It rotates freely in the overrun direction and immediately locks in the drive direction. This is the internal one way clutch inside the pulley that allows the insides of the alternator to stop when the engine is shut off. This overrun feature eliminates the belt chirp noises during engine shutdown as well as during transmission shifting.

How to test an alternator clutch pulley?

To test an alternator clutch pulley first the top plastic cover has to be removed. Then stop the rotation of the pulley and spin it. It will move freely if it is alright and it will move only in one way and stop moving in the other direction.

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Alternator Not Charging Battery But Alternator Is Good.


How do you know if your alternator pulley is bad?

There are few signs of the alternator pulley when there is a problem in it. The first is excessive tensioner movement. If a short buzzing of 1 to 5 seconds is heard after shutting down the engine it signals that the alternator might have to be replaced. There can also be a chirping sound caused by the worn out bearing when the engine is starting or shutting down.

How do you check an alternator clutch pulley?

A properly functioned alternator pulley will work smoothly without any chirping or flapping noise. But if there is any abnormality in the engine it will give signals and it’s better to keep it on check. To check an alternator clutch pulley first its plastic cover has to be removed then try spinning it. If the alternator is fine it will spin smoothly and will stop if moved backwards.

What does an alternator clutch pulley do?

An alternator clutch pulley is a one way clutch mechanism. It rotates in the overrun direction and stops moving when in drive direction. This is a one way clutch that helps the insides of the alternator come to a halt immediately when the engine is shut off.

Should the alternator pulley move freely?

Yes, the alternator pulley should move freely in the overrun direction and come to a stop in the drive direction. It helps the alternator to shut off right away after the engine is shut. Its overrun feature removes the belt chirp noises during engine shutdown.

How do you Unseize an alternator pulley?

It is actually a very simple task to unseize an alternator pulley. Put a bit of motor oil, transmission fluid or even old motor oil will work. Then put a socket in the breaker bar and move the seized pulley back and forth. The first movement can get difficult but once done it will start moving like a brand new one.

What does a bad alternator pulley sound like?

A bad alternator pulley initially will cause excessive tensioner movement. A short buzzing or chirping sound can be heard for 1 to 5 seconds after shutting down the engine. The sound can also be heard during engine start. It is because of the worn out bearing and it can cause further damage to the belt.


Finding the exact problem of the alternator clutch pulley is very important to fix it at the right time. Sometimes the issues might not be big but avoiding the little problems can make it bigger. If you are facing chirping, growling or whining noises coming from under your car hood, facing battery issues, having trouble starting the car, headlights getting dim or too bright or the car smells of burning rubber or wire than it is time for you to get a check-up done of your alternator clutch pulley.

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