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Strapped for cash this holiday season? Replacing an alternator can cost you several hundred bucks at the local repair shop, but it’s one of the simplest repairs you can do at home. With a few tools and about an hour you can swap it out yourself — and keep your dough in your pocket where it belongs. In this case we’re replacing an alternator on a ’95 GMC truck, however the process is very similar for most vehicles.

Note: As this is a Craftsman-sponsored project, you’ll notice a number of Craftsman tools in the photos. But here’s a secret: we already owned ’em all. They’re the same tools we’d have used if they weren’t sponsors. Really!

First and most importantly: disconnect the battery. There may be several wires or just one wire on your alternator, but rest assured that one of them is hot. If you don’t disconnect the battery, you’re very likely to end up grounding a live wire during the process. This causes all manner of bad things to occur — not the least of which is giving you quite a shock.

Now that the battery is out of the way, disconnect the wire or wires from the back of the alternator. This is usually a very simple process but if you’re unsure as to where they go, label them as you take them loose.

Every project has a tough spot, and this is the tough spot for alternator replacement: remove the belt from the pulley. Somewhere on your vehicle there is a tensioner pulley. You’ll need to move it enough to slip the belt off the pulley. Our ’95 GMC has a standard spring-loaded GM tensioner that required us to pull it back with a wrench. On some vehicles you’ll find screw-type or rod-end type tensioners that apply tension by turning a bolt through threads to increase/decrease the length of a rod. In this case, just turn the bolt/rod-end with a wrench or socket until it releases enough tension to allow you to remove the belt.

In our case we grabbed a Craftsman 17mm Cross Force wrench and pushed hard. Normally that would be a pretty painful experience, but the Cross Force was designed for just such a situation. There’s a 90-degree twist in the middle of the Cross Force wrenches, so you end up pushing on a flat surface. The result: we could push harder without discomfort. So we just laid into it and the belt came free.

Once the belt is off just remove whatever bolts connect the alternator to the bracket and you’re good to go. Our model required the removal of three bolts: one at the front and two at the rear.

Read on to page two for our How To.

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20 Responses to How-To: Replace An Alternator

  1. Clark F says:

    I own basically the same truck, and yes, replacing the alternator was, “one of the simplest repairs you can do at home”. I replaced mine do to junk bearings a few months ago. But dont be misguiding. Ever tried replacing a newer VW alternator? If I remember right, book time on it is 3 or 4 hours, and involves disassembling the entire front end, moving the radiator to the “service” position, and finally replacing the alternator.

  2. KMR says:

    Much of the work to pull the alternator on our S10 shop truck has to be done through the passenger side wheel well opening into the engine bay. If you’ve never done it before, and I hadn’t, it wasn’t fun. Putting it back in went much faster, but I couldn’t believe when I opened the manual and the first instruction was to jack the car up and remove the passenger side front wheel.

  3. Jesper says:

    Just make sure you know how to wind the belt back through all the different pully’s. On my Mom’s Chevy Cavalier there was a diagram on the inside of the hood. Not sure how all the other cars diagram it. I haven’t had to touch the alternator on my VW Golf yet. I guess it’s a good rule of thumb for any car repairs, make sure you know what it looks like on before you take a part off. Take photos if necessary. It was a tight place to work as well. In some instances a long handle on the wrench that fits on the tensioner bolt helps with leverage in those tight places. Sometimes a shorter handle is necessary just for clearance.

  4. Harry says:

    Just remember when disconnecting the battery to remove the negative cable FIRST and reinstall it LAST to prevent unwanted arcing.

  5. Adam R. says:

    My favorite alternator so far has been on a 2000 Malibu. You have to jack up the engine and disconnect two bolts from the engine mount to route the belt.

  6. Toolhearty says:

    [i]Adam R. Says:
    December 23rd, 2008 at 5:22 am

    My favorite alternator so far has been on a 2000 Malibu. You have to jack up the engine and disconnect two bolts from the engine mount to route the belt.[/i]

    That’s insane. Someone should be shot.

  7. Joe says:

    One little added tip–have the local parts store test your alternator before you buy one, even if you’re planning on going to the junkyard, there are plenty of other problems that can fool you into thinking it’s the alternator. Saves time and money.

  8. KMR says:

    The parts store has one goal in mind: selling you parts. Autozone’s alternator tester only gives a PASS / FAIL result, I can’t trust a diagnosis that doens’t give me data to qualify the result.

    If you have a decent multimeter there are a whole host of test procedures you can carry out to diagnose a charging system issue before you even remove the alternator. If you’ve got access to a DC clamp on ammeter, it’ll make the job easier, but they’re not common and expensive to buy.

    Oh and, THE AUTO-REFRESH SUCKS! People are going to stop posting because of the auto-refresh issues

  9. PeterP says:

    On my old Saturn, I had to remove the passenger side wheel, a fair amount of plastic trim, and ultimately get a helper because the thing was in such an awkward position. This is one of those conceptually simple repairs made difficult by auto manufacturers that simply don’t care about maintenance costs.

    I actually wish someone would rate cars by ease of repair. I don’t know how many people would actually care about it, but it would make a difference in my car buying choices.

  10. fred says:

    I had one of those 2000 Malibus that shredded its belt – luckily on a week end.

  11. Mike Y says:

    This was one of my favorite money saving things when I owned a BMW 325e (years ago). Great car, but repair costs were like having your own personal Space Shuttle.

    Dealer wanted $350 for a rebuilt alternator (plus labor!). I found out the name of the shop that actually rebuilt their alternators. Turns out he only charged $40 to do the rebuild. A half-hour of wrenching (each way) got it done.

    This must have been about 18 years ago, but the price differential probably still stands, if not the same prices.

  12. BC says:

    My worst experience was with a ’98 Buick Skylark – 3100 V6. The tensioner pulley had a 3/8″ square hole in it, but there wasn’t enough room to get a ratchet between the pulley and the strut tower. It was a friend’s car, and I was just trying to help her out, but that one wound up going to the shop to get the job done – glad it wasn’t mine.

  13. stephen colbert says:

    My 1999 Subaru Legacy wagon is great to work on, especially for an alternator. I would recommend Subaru (to PeterP) as a car that is “easy to work on.” Choose an engine like the H-4 where you have plenty of room or a Scotch-Yoke Kinematic Design. I just did my alternator and it took 1.3 hrs including going to Autozone to get it tested (along with the batt) and replacing the alternator. Additionally the plugs, wires, coil packs, oil, belts, and other basic maintenance tasks are relatively easy to do compared to the crammed engine bay of my ’92 Chevy Lumina 3.1L.

  14. strizzy says:

    Check with a local alternator rebuild shop, sometimes they can be fixed for not much money at all. A lot of times the diodes go on them, not very expensive for a specialty shop to replace.

  15. Old Donn says:

    Ran into the same dilemma with my 99 Grand-Am as Fred & Toolhardy did with their Chevys. My most interesting alternator job was on my 02 Astro. You can’t get at the bolts, the whole bracket has to come out.

  16. Coach James says:

    My ’96 Saturn was also a remove through the front passenger wheel well. I spent 5 hours on the side of the road, in the rain replacing it on a trip one time. Designers should be forced to fix what they design.

    And I second the hatred for aiuto refresh. And I’ve already cut back on my posting because of it. I can’t fathom why it is still on here.

  17. Old Donn says:

    Hey Coach, the quick answers to your entry about designers. 1) Putting that stuff on during assembly is a snap. And, 2) They don’t want us working on their cars.

  18. Coach James says:

    Agree with you on both points, but I really do think design would be improved if designers did more repair work themselves.

  19. Old Donn says:

    You’re right, Coach. That noise you heard was me screaming at the GM Tech Center.

  20. Dan B says:

    Surprised no one has mentioned to go ahead and put the battery on a charger while you are installing the alternator. Some vehicles have a starter that will incur damage if engaged with less than 9 volts.

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