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Alternator Belt Replacement

Updated on November 4, 2015
Jaguar diesel engine shot at the 2006 London Motor Show
Jaguar diesel engine shot at the 2006 London Motor Show | Source

An alternator belt replacement job is a relatively simple repair procedure in most vehicles. You only need some common tools, which you might already have in your toolbox, and a couple of hours of work on a Saturday morning in your own garage.

Depending on your particular vehicle model, your engine uses a drive belt or serpentine belt to run the alternator. Regardless of the type of belt your alternator runs on, the belt stretches and deteriorates after miles of service, developing tears and splits. You'll see these signs of wear on an aged drive belt. However, serpentine belts, commonly made with EPDM (ethylene-propylene terpolymer), rarely show their age, which makes it important to follow the manufacturer service interval.

Operating your alternator with an old, worn-out belt is unsafe and costly. If the drive belt or serpentine belt breaks on the road, you'll only have a few minutes of driving time before your battery power drains out and all electrical devices go out, leaving you stranded.

This guide helps you install an alternator belt replacement, whether your vehicle uses a drive or serpentine belt.

Worn out drive belt on a Toyota Corolla.
Worn out drive belt on a Toyota Corolla. | Source

Replacing an Alternator Drive Belt

Before you start, check for other accessory belts in front of the alternator belt, 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). To remove these other accessory belts, follow the same procedure described next to remove the alternator belt, if necessary.

Removing the Drive Belt

1. Note how the alternator belt threads around the accessory pulleys so that you install the new one following the same path. Some vehicles have a decal on the engine compartment that shows the belt routing. If not, make a simple sketch of the belt's position using a pencil and notepad to guide you during the installation, if necessary.

2. Remove any accessories like the air filter assembly to gain access to the alternator.

3. To remove the alternator belt, loosen the pivot bolt or nut and the locking bolt using a wrench and ratchet. On some vehicle models, you can't access these bolts from the top of the engine. You'll probably have to raise your vehicle using a floor jack, support it on two jack stands, and maybe remove a splash shield from under the engine compartment to access the bolts from underneath.

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

5. Remove the drive belt from the pulleys.

Installing the Alternator Belt

1. Route the new alternator belt over the corresponding pulleys.

2. Then, look for a square hole or a cast lug on the alternator mounting bracket assembly. If you find a square hole, 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. Some 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.

4. Tighten the bolts and nuts snugly to hold the alternator in position. 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, if you have enough room to position the pliers.

Maintenance and Repair Automotive Manuals

Haynes Publications, Inc. 24048 Repair Manual
Haynes Publications, Inc. 24048 Repair Manual

Using A Haynes Manual Is Like Having A Mechanic In Every Book, Each Manual Is Written And Photographed From The Hands-On Experience Gained By A Complete Teardown And Rebuild Of The Engine, Includes Procedures For Everything From Routine Maintenance To Complete Engine Overhaul


Checking the Alternator Belt Tension

1. Before you tighten the bolts, check for proper belt tension. 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.

An easy way to do this 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. Or use a belt tension gauge. A good investment if you have more than one vehicle you need to service.

Make the Necessary Adjustments.

* If the belt has too much tension, it'll put too much stress on and damage the accessories' bearings, and damage the belt itself.

* If the belt is too loose, it will slip, become noisy, vibrate and get damaged; plus the charging system won't operate properly. And if the belt runs you water pump too, the engine will overheat. So, once the has the correct tension:

1. Tighten the pivot bolt or nut and the locking bolt.

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 and turn off the engine.

Signs of a Worn Out or Damaged Alternator Belt

Replacing a Drive Belt

Serpentine Belt Replacement

You don't need to loosen the alternator when replacing a serpentine belt. But, you still need to thread the belt correctly around the different pulleys. Look for a decal on the engine compartment that shows how the belt runs around the pulleys; or make a sketch of this yourself on a piece of paper. This will save you from installing the belt incorrectly and prevent many engine systems problems.

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 loan you for free. 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.

2. Once you've removed the 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. Most manufacturers recommend replacing the belt tensioner when replacing the belt to prevent problems as well.

5. Then, install the new serpentine belt following the same procedure you used to remove the belt.

6. Visually check that the belt lines up properly on each pulley and the ribbed side of the belt faces the ribbed pulleys.

Serpentine belt.
Serpentine belt. | Source

You can do an alternator belt replacement job at home in about one or two hours with a few common tools and save some money in the process. But remember that it's also easy to turn a relative simple job into a source of problems for the charging system, cooling system, and the accessories where the belt rides on. When installing the new belt, make sure to tense the belt and torque the bolts correctly.

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