How to Change your Alternator

Electrical system failure is a common problem in aging cars. There are several things that can go wrong with an electrical system as parts age, wire insulation cracks and connections corrode. A common problem with older vehicles is the alternator. This is the part which uses some of the energy from the engine to charge your battery and power your accessories. Without a properly functioning alternator your battery will run down after about an hour or so of your engine running by sheer draw needed to fire your sparkplugs. The more accessories that are running, the faster the battery will die.

Commonly when the alternator in the car begins to fail you will notice a dimming in the lights on your dash panel, as well as your headlights etc. Commonly reving the engine will cause the lights to brighten, and when you take your foot off the gas, the lights dim again. You may also hear a squealing or growling noise coming from the engine compartment. Don’t confuse a slipping belt with a worn alternator however. A slipping belt, resulting from poor belt tension, or a worn out belt will cause a squealing noise as well. The best way to diagnose this problem is to first determine that the cars battery is not the problem, likely if you have noise associated with the problem this is not the case, however, check the battery first regardless. Make sure your terminals are connected tightly; you should not be able to move the wires which are attached to the terminals of the battery, as well as the alternator, and starter. If they are loose, tighten them and see if your problem is still present. If the car starts easily and the symptoms only present themselves when the car is idling it is likely not the battery. Just to make sure however, charge the battery on a charger outside of the car, and then apply a load tester to ensure the battery is able to hold a charge. If the load test passes, the problem is likely the alternator. If you are unsure, it is best to get a mechanic to check the problem out. However if you are reasonably sure the problem is the alternator it can be quite easily replaced.  In case at this point you are confused as to which part on the engine the alternator is, simply go online and look up your model of car and you should be able to find a diagram of where the alternator is and what it looks like.

Some alternators can also be rebuilt, by replacing internal bearings, and can be done so cheaply, however the process is more involved, so for the sake of this article we will not be covering alternator rebuilding/repair.

To replace a worn alternator, first disconnect the positive lead on the cars battery, to ensure that nothing will arc while messing around under the hood. This is a good habit to get into when doing any repair work in close proximity to the electrical system. Don’t forget when you’re all done to re-connect the wire to the terminal however, or you will be going no-where.

Once the battery is disconnected, unplug and disconnect all wires from the alternator, remembering or marking which wires went where, so that you know how to connect the replacement. Write it down if you have to, draw a little picture, use tape as a label, just don’t forget. Electrical parts do not like to be hooked up incorrectly.

Next you must remove the belt which powers the alternator off of the engine. Some engines use V-belts and others use a serpentine belt. Engines that use a V-belt generally adjust tension on the alternator belt right at the alternator itself. You may see a bolt in a channeled bracket. If the bolt is loosened the alternator will swing allowing more or less tension to be put on the belt. Or the bolt itself may regulate the tension itself. Either way, this should be obviously visible at the alternator. Loosen the tension on the belt so that it can be pulled off of the alternator pulley. Leave it on the other pulleys of the engine, there is no need to remove it further unless you are replacing the belt at this time as well. Then simply find the bolts holding the alternator to the engine and remove them. The alternator can then be removed. Replace it with the new one, bolt it in place, and replace the belt applying tension to the belt before tightening the bolt which holds it from swinging. You may need to use a prying instrument to get significant tension on the belt before locking it in place. Once the alternator is secure, check the tension by pushing on the belt like you would strum a guitar. There should be some give, but the belt should not be floppy.

If the engine has a serpentine belt, the alternator will be powered by this belt, as this is the only belt present. Generally these belts are tensioned by a spring loaded auto-tensioner. This will usually look like a pulley on a small bracket arm. You can pull up or push down on this device and it will move, removing tension from the belt. There will be a small square hole into which you can place a ratchet to give you leverage for this task. Remove the tension using the ratchet with one hand and slip the belt off of the alternator pulley with the other. Let the belt stay on the other engine pulleys. Unbolt the alternator and swap it for the new one. Bolt the new alternator in place. Replace the belt and re-connect the wires as they were connected to the old alternator. Re-connect the batteries positive lead and make sure all connections are tight. Ensure all of your tools are out of the engine compartment and any rags or cloths are also clear. Ensure the belt is correctly on all pulleys of the engine and not loose. Finally, start the car. If everything starts and runs, close the hood and test drive the car.

If you are unsure about what you are doing, consult a mechanic. This is not an overly difficult job, and as long as you take care to pay attention to what you are doing, no harm should come to you or your vehicle.