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Car Alternator Replacement Job

Updated on October 21, 2015
Car alternator replacement job.
Car alternator replacement job. | Source

For a car alternator replacement job you don't need special skills. But you need to follow the correct steps to avoid damage to electrical components during the procedure and ensure that the charging system will operate right after your repair.

You know you have to remove the mounting bolts and some electrical wires from the back of the alternator, but beyond that you may not know exactly how to proceed. You probably already have all the tools for the job like wrenches, ratchet, ratchet extensions, pliers, sockets, screwdrivers, and pry bar. Still, depending on your particular vehicle make and model, you'll need to remove one or more components, take important safety precautions, and follow a particular procedure to access and replace the alternator successfully.

Either way, on most vehicles you can do this repair job yourself in your own garage in about an hour or two using a few common tools, and save some money in the process. You'll spend between $100 and $500 dollars for the alternator - depending on your particular model - but you'll save around $200 or more in labor costs following this guide.

So, let's start.

Tools You'll Need
Wrench set
Ratchet extension
Socket set
Floor jack, 2 jack stands and 2 wooden blocks - if necessary
Pry bar or breaker bar, if necessary

Removing the Bad Alternator

On most modern vehicles, car manufacturers recommend using a Car Computer Memory saver, which connects to the cigarette lighter, before disconnecting the battery. It'll preserve the engine control settings, transmission shift settings on some vehicle models, alarm settings, as well as the memory of other vehicle modules, if equipped, plus your radio and clock settings.

Disconnecting the battery without the means to preserve modules' memory, the car computer will have to go through a relearning process, which will take a few miles of driving — up to 100 miles in some cases — before the engine and other systems stabilize. On some specific models, you'll need a scan tool to reset the modules. Check your owner's or repair manual, if necessary.

1. Disconnect the negative terminal from the battery using a wrench, and secure the terminal away from the battery post to keep it from accidentally touching the post during your repair. This will prevent any potential short circuits from damaging sensitive electrical or electronic components while you work on your alternator.

2. Now, check whether you have enough room to remove the alternator from the top of the engine compartment. Usually, you need to remove the air filter assembly, like the air duct, air intake tube, and heat shield. Sometimes, you'll need to remove one or two other components as well, depending on your particular model.

3. On some models, you have to work through the bottom of the engine compartment. If so, you may need to remove a splash shield from under the engine compartment. For this, use a floor jack to raise your vehicle and support it safely on jack stands. Then, block the rear wheels using a couple of wooden blocks, and engage the parking brake.

4. Crawl under the vehicle and remove the shield.

5. Now, you need to remove the drive belt or serpentine belt from the alternator drive pulley. Before you do that, make sure to note the belt's routing so that you reinstall it correctly if it slips off the other accessory pulleys as you work on the alternator. Depending on your car model, this belt may drive the water pump, air-conditioning compressor, steering pump, or some other accessory. Most vehicles have a decal on the engine compartment showing the belt routing. Double check that your belt follows this same route. If not, sketch the route on a piece of paper for later reference.

6. On most engines, two or three bolts hold the alternator in place. To remove the drive belt (if your engine uses a serpentine belt, go to the next step), start loosening the alternator mounting bolts (adjusting, pivot and locking bolts) using a ratchet, ratchet extension, socket, and wrenches. This will let you swing the alternator on its mounting bracket and slip the belt off the alternator pulley.

7. Vehicle models with a serpentine belt offer a more friendly way to remove ― and reinstall ― the belt. To remove this belt, rotate the spring-loaded belt tensioner against the spring force (to rotate the tensioner, you'll need a wrench, or ratchet or breaker bar with a half-inch drive). This will release the belt's tension, and allow you to slip the belt off the alternator pulley. Once the belt is off the pulley, slowly let the tensioner spring back into place.

8. After removing the drive or serpentine belt, completely remove the mounting bolts while holding the alternator in place with one hand. Note where each bolt goes since they have different length. Then, carefully rotate the alternator and disconnect the electrical wires and wiring harness from the back of the alternator. Note which wire connects where so that you install each one back in the correct place. Then, remove the alternator from your vehicle.

Removing the Drive Belt

Installing the New Car Alternator

To install the alternator follow the same procedure in reverse order.

1. Position the alternator in place and plug in and connect the electrical harness and wires to the back of the alternator.

2. Loosely fit the alternator's mounting bolts — don't tighten them yet, unless you have a serpentine belt.

3. Slip the belt over each of the accessory pulleys, if you have a drive belt. If you are installing a serpentine belt, leave the pulley you have the easiest access to for last.

4. If you're installing a serpentine belt, rotate the belt tensioner as you did before. Slip the belt over the last pulley and carefully release the tensioner. Then go to step number 8.

5. If you're installing a drive belt, pull the alternator away form the engine using the pry bar to tense the belt. On some alternators, the mounting bracket comes with a square hole for a 1/2-inch drive breaker bar for this purpose.

6. While keeping the alternator in position and the belt stretched, use the thumb from your free hand — or ask an assistant to do this for you — to press on the belt's middle section — the section that runs between two of the pulleys with the longest stretch. The belt should deflect between 1/8 to a 1/4 of an inch, if the distance between the pulleys is 12 inches or less; or between 1/8 to a 3/8 of an inch, if the distance between the pulleys is over 12 inches.

7. Once the belt has the correct tension, tighten the mounting bolts.

8. Double check that you routed the belt correctly, aligned it over each pulley, and tightened all the electrical connections on the back of the alternator.

9. Reinstall the splash shield and lower your vehicle off the jack stands, if you had to raise it.

10. Reinstall any accessories you had to remove.

11. Then, reconnect the battery's negative terminal.

12. Turn the ignition key to the On position, but do not start the engine yet. Verify that the charge light on the dashboard panel illuminates. Then, start the engine and verify that the drive belt is not wobbling. If it is, give more tension to the drive belt. Or, if your car uses a serpentine belt, you'll need to replace the worn out belt tensioner.

Replacing the Alternator

When on a car alternator replacement project, the most important part of your job is to work safely to prevent personal injuries and damage to other components. Although you don't need experience or special skills to do this repair, you still may run into difficulties on some specific vehicle models. When necessary, read the instructions on replacing the alternator that come in your repair or service manual for your particular make and model. The manual will help you clear up any issues you may encounter. Buy an inexpensive, aftermarket manual online or from your local auto parts store. However, if you don't want to buy the manual yet, you may consult a copy in the reference section of your local public library.

Find Your Repair Manual

Ford Mustang 2005 thru 2014 (Haynes Repair Manual)
Ford Mustang 2005 thru 2014 (Haynes Repair Manual)

With a Haynes manual, you can do it yourself. From simple maintenance to basic repairs. Haynes writes every book based on a complete teardown of the vehicle. We learn the best ways to do a job and that makes it quicker, easier and cheaper for you. Our books have clear instructions and hundreds of photographs that show each step. Whether you're a beginner or a pro, you can save big with Haynes!


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