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How to Install an Alternator Belt

Updated on June 14, 2018
Dan Ferrell profile image

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

Jaguar diesel engine shot at the 2006 London Motor Show
Jaguar diesel engine shot at the 2006 London Motor Show | Source

Knowing when to replace an alternator belt is not an issue if the belt breaks apart, or it shows clear signs of wear:

  • Cuts
  • Tears
  • Splitting
  • Deterioration
  • Glazing

But, it can get confusing when you want to do some preventive maintenance and your old drive belt or serpentine belt still looks good after all those years of service. The problem is especially with newer serpentine belts made of EPDM (ethylene-propylene terpolymer), which rarely show their age.

Whether you want to replace a worn out belt or do some preventive maintenance to avoid getting stranded by the side of the road, you can do this repair at home yourself.

Replacing a belt is a relatively simple repair procedure in most vehicle models. Usually, all you need is a few simple tools and a couple of hours on a Saturday morning in your garage.

And this guide helps you make the installation. First, we follow the steps to replace a drive belt; then we follow the procedure to install a serpentine belt.

Worn out drive belt on a Toyota Corolla.
Worn out drive belt on a Toyota Corolla. | Source
I. Replacing an Alternator Drive Belt
II. Replacing a Serpentine Belt
III. When to Replace the Alternator Belt

I. Replacing an Alternator Drive Belt

Before you start, check for other belts that might be running other accessories like the steering pump, oil pump, or fan belt (some vehicle models have two or three accessory belts, but one or two drive belts is more common). If you need to remove one or more of these other belts to gain access to the alternator belt, you can follow the same procedure described next to remove the alternator belt.

A) Removing the Drive Belt

  1. Make a note of the path your alternator belt follows (what accessories it runs), so that your new belt follows the same path. Some vehicles have a decal on the engine compartment that shows the belt routing. If not, make a simple diagram of the belt's routing on a piece of paper that you can refer to during the installation.

  2. Remove parts or components like the air filter assembly or radiator fan shroud, to gain access to the alternator. Depending on your particular model, you may have to remove the fan and fan pulley as well.

  3. On the alternator, loosen the pivot bolt or nut and the locking bolt using a wrench and ratchet. With some vehicle models, you can't reach these bolts from the top of the engine. You'll probably have to raise your vehicle using a floor jack. In this case, support the vehicle on two jack stands, set the parking brake and chock the rear wheels. Now you can access the bolts from underneath.

    NOTE: On some models, a transverse bolt (jackscrew) on the alternator mounting assembly provides tension to the drive belt. Look for this screw behind or underneath the alternator. You need to unscrew this bolt a few turns to loosen belt tension to remove the belt.

  4. Once you've loosened the alternator bolts, pivot the alternator toward the engine to remove belt tension.

  5. Slip the old belt off the alternator pulley and the rest of the pulleys it runs.

  6. When buying the new alternator belt have the information of your car ready like year, make, model, and engine size, to get the correct replacement.

B) Installing the Alternator Belt

Before installing the new belt, match the old alternator belt to the new one to make sure you have the correct replacement.

  1. Route the new alternator belt following the same path from the old belt. Center the belt vertically on each pulley to avoid damage to the new belt when running.

  2. Look for a half-inch square opening or a cast lug on the alternator mounting bracket assembly. If your alternator mounting bracket has one, use a breaker bar with a 1/2-inch square drive to lever the alternator and provide tension to the belt. If your alternator has a cast lug, use an open wrench to lever the alternator.

  3. Other alternators do not provide a square hole or cast lug. So you need to lever the alternator by hand or by using a pry bar for the same purpose, being careful not to damage the alternator's case or some other component.

    Or ask a helper to lever the alternator away from the engine to stretch the drive belt while you finish installing the belt. Another way to temporarily hold the alternator in place is to use a pair of vise grip pliers as a stop on the alternator's mounting bracket, against the adjusting bolt. This may work if you have enough room to position the pliers.

  4. Hold the alternator in position and check the belt tension.

NOTE: Some alternators use a transverse bolt to provide tension to the belt. If you need help with the proper belt tightening procedure for your particular model, consult your vehicle repair manual. If you don't have this manual, you can buy a relatively inexpensive aftermarket copy at Amazon, like this Haynes manual. Haynes manuals come with step-by-step procedures for many maintenance, troubleshooting and parts replacement repair projects. So the manual is a excellent investment.

Check all accessory pulleys for proper operation before installing the new belt.
Check all accessory pulleys for proper operation before installing the new belt. | Source

C) Checking Alternator Belt Tension

Before you tighten the bolts, check for proper belt tension. The best way to do this is using a belt tension gauge. However, you still can do it without a gauge following the next procedure:

  1. Locate the stretch of belt with the largest span between two pulleys. The stretch between the alternator and the engine crankshaft pulleys, for example.

  2. Now, using your thumb, push down on the belt at the midpoint of the stretch.

  3. See how much the belt deflects. You want the belt to deflect between 1/8- to 1/4-inch, if the distance between the centers of the two pulleys is less than 12 inches. Or between 1/8- and 3/8-inches, if the distance is more than 12 inches.

    One way to measure how much the belt is deflecting is to position a ruler perpendicular to the belt at the point where you are pushing down on the belt and see how much the belt deflects.

  4. Once the belt has the proper tension, tighten the alternator bolts.

D) Checking Belt Operation

Proper belt tension is important:

  • If the belt has too much tension, it may damage bearings and bushings on those accessories it runs; tension can glaze or even break the belt itself.

  • If the belt is too loose, it will slip, become noisy, vibrate, prevent the charging system from working properly, or even slip off a pulley. And if the belt runs you water pump too, the engine will overheat.

So, once the belt has the correct tension:

  1. Tighten the alternator pivot bolt or nut and the adjusting or locking bolt to the torque listed in your vehicle repair manual. Use a torque wrench for this.

  2. Reinstall the other belt or belts you had to remove to access the alternator belt, following the same procedure you used to install the alternator belt.

  3. When ready, start the engine and apply the parking brakes. Then check the belt to make sure it is running properly. The belt should run quietly and should not flutter; otherwise, the belt is loose and needs adjustment. Let the engine idle for about 15 minutes to allow the belt to seat properly and stretch.

  4. Then, turn off the engine.

If you still need to get some visual clues about replacing the drive belt, you can watch the following video.

Replacing a Drive Belt

Making a Complete Service Maintenance Repair

Besides replacing the serpentine belt, manufacturers recommend replacing the automatic belt tensioner and idler pulleys to extend the serpentine belt service life.

II. Replacing a Serpentine Belt

Before proceeding to remove the belt, look for a decal on the engine compartment that shows the belt path around the pulleys; or make a sketch of the path yourself on a piece of paper. This will serve as a reference when installing the new belt.

  1. To remove the belt use a breaker bar or a large ratchet with a 3/8 or 1/2-inch drive to swing the tensioner arm (belt tensioner) to remove the tension off the belt. On some models you'll need to use a large wrench for this, or even an auto-tensioner tool, which some auto parts stores will lend you without charging you for it. Still, on other models you need to turn a drive bolt to release the belt tension. If necessary, check the vehicle repair manual for your specific make and model.

    NOTE: If your vehicle doesn't have a belt tensioner, it's probably using a stretch belt. You need to cut this belt to replace it and use a special tool for installation. Check your car owner's manual or vehicle repair manual for more information.

  2. Once you've removed tension from the belt, slip the belt off one of the pulleys it rides on.

  3. Slowly release the belt tensioner.

  4. Before installing the new belt, check that all the accessory pulleys - including the belt tensioner pulley - rotate freely. You may want to replace the belt tensioner at this time, since the tensioner is subject to wear as well.

    Check all the pulleys for noise, alignment, and dirt. Rotate each pulley by hand to check for roughness and noise. You can use a straightedge to check pulleys' alignment. If any pulley is noisy or out of alignment, make sure the accessory is correctly mounted and the mounting bracket is not damaged; replace that component or accessory, if necessary. You can remove dirt and debris from pulley grooves using a wire brush.

  5. Buy the new belt for your application using the year, make, model and engine size of your vehicle to get the correct replacement.

  6. Compare the old belt to the new one to make sure you have the correct replacement. The old belt might be slightly larger, but should have the same width.

  7. Then, install the new serpentine belt following the same procedure you used to remove the belt. Make sure the ribbed side of the belt faces those pulleys with grooves.

  8. Visually check that the belt is vertically centered on each pulley. Otherwise, remove the tension and correct the belt position.

  9. Once the belt is installed, start the engine and check belt operation.

  10. The belt should run quietly and should not flutter; otherwise, there's a problem with the belt tension. Make sure the belt tensioner is working properly or that you installed the correct belt for your application. If your alternator uses a decoupler pulley, check it as well.

  11. Let the engine idle for about 15 minutes to allow the belt to seat properly and stretch.

The following video can give you some visual reference that might help you complete your serpentine belt replacement job.

III. When to Replace the Alternator Belt

You can learn how to replace an alternator belt in a few minutes. But knowing when to replace the belt may not be that simple sometimes.

A drive belt has an average service life of 4 years. So you can replace your drive belt every four years, or follow the service maintenance schedule recommended by your car manufacturer. However, you need to replace the belt before the recommended service interval if it shows signs of wear. You can find the service schedule in the vehicle repair manual for your particular make and model.

Serpentine belts in used today are hard to inspect by sight. But you still can follow your car manufacturer service schedule or use a serpentine-belt gauge.

Just remember that operating your alternator with an old, worn-out belt is unsafe and can turn into an expensive repair. Keep this guide handy and use it to replace an alternator belt or serpentine belt as necessary.

Serpentine belt.
Serpentine belt. | Source

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© 2015 Dan Ferrell


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