How to Change an Alternator

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When changing an alternator on a car, the first step is to loosen up the negative battery terminal and the belt tension. Remove the bolts and set them aside when removing an alternator with help from an auto mechanic in this free video on car repair and diagnostics.

Part of the Video Series: Auto Repair & Diagnostics
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Video Transcript

Hello. My name is Tom Brintzenhofe. I'm a certified master mechanic from Redding Pennsylvania. Today we're going to talk about how to change an alternator. First thing you want to do; always be safe, wear your safety glasses. Your eyes are one thing that can't ever be fixed or replaces, so always be safe and do that. There's several different kinds of alternators, the configuration is a little different. This is a typical Ford; two plugs; kind of; if you can see the position compared to the two bolt holes. Here's a typical Chevy alternator. It has a single plug, single battery port on the back. Again the two bolt holes are off set. This jeep here has got an additional two holes, not similar to either one of these two. The first thing you want to do on this one is loosen up your negative battery terminal. You never want to work on anything electrical with your battery hooked up. The second thing you want to do is your belt tension on here, loosen that up so you can get your serpentine belt out of the way. Unfortunately you won't be able to see that on this vehicle, so I have one sitting here. As this is bolted to the engine, you have; your belt runs up over it. You have a little port right here your ratchet fits right into. As this bolts to the engine; as you turn on this it will either tighten or loosen it. It's got a spring in here that keeps the tension on the belt. So, you want to take that off first. Take the tension off. Get your belt off. Disconnect your main battery terminal here and your plug on the back of the alternator. Your two bolts; take them off and set them aside somewhere close by so you won't lose them. We all know how that is on a weekend; working on a Sunday. You end up dropping a bolt, you can't find it, and the parts stores are all closed. It just makes for a bad afternoon. Pull your alternator off. The first thing you want to do, once you get the alternator off; like I say. Your pulleys don't always come from your parts stores identical to what's on your vehicle. As you see this one has got a six groove serpentine belt. This one's got a single groove. Now, when you get them from the parts store a lot of time they don't match your vehicle, so you have to change them. On the front is the twenty-one millimeter nut, you've got a socket and sometimes you can get it with a ratchet, other times you might have to take it to a local garage and get it with an impact gun. Switch them off. Put the correct one on. Sometimes you'll have to take it off the alternator you have, put it back together the same way you got it. Most of the time you might have to check with your repair manual for your specific vehicle; every vehicle is a little different. Put it back together the same way you took it apart. Run your serpentine belt back the way; like I said every vehicle is a little different, so you might have to either pay attention to what you're doing; a lot of times it will be marked right on the vehicle how the belt goes. Put your belt back over it. Hook your battery backup. Before you start it the first thing you want to make sure on your battery is you have at least 12.5 volts. This one's got 12.6. If you have everything all back, hooked up again, when you start this vehicle up; don't forget to tighten your battery terminals by the way. You should have at least thirteen volts on it when all is said and done. Now, when you start it up, everything is all good. You should have 13 volts on it. Let it run for a little bit. Check it again in about a minute or so. Like I said, make sure you're got thirteen volts. If you've got thirteen bolts you're good to go. That's about all there is to it; changing an alternator on a vehicle.

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