How to Repair Your Own Alternator (With Simple Tools)

How to Repair Your Own Alternator (With Simple Tools)

In this video, you and I are going to troubleshoot and then fix a problem with this alternator. Now, before we start the’res one very important thing that we’ve got to do… Can you guess what that is? Exactly: put some white paper on top of your work surface and don’t ever trust anybody does a job like this without white paper! This alternator was removed from the car once I was sure that there were no other issues on the vehicle itself so I’ve checked the wiring, I’ve done voltage drop checks and I’ve also check the belt tension – all the simple things that could have been wrong with the vehicle. So let’s start with the really simple things first – before we start getting into deep and breaking things down – let’s just check… This particular alternator like many others has a slip pulley, so the first thing to do is just hold the rotor still – stick a screwdriver in to the case – and then in one direction you should be able to turn that nice and smoothly and in the other direction it should be rock-solid, so do your best try and turn it… Ok that is rock solid so i’m satisfied that the clutch isn’t slipping. That could have been another cause of the non charging issue that I had. On this particular alternator you will see it’s got this strange attachment to it – it’s an oil-driven vacuum pump for the brake servo. Most alternators don’t have these and that makes it a lot easier to get the alternator on and off the car. Before we start disassembling the alternator, there is a simple test we can do (we should have done this on the car but let’s pretend that we haven’t done that) so we’re going to put the multimeter on to the continuity check and then we want to go from the battery positive terminal and then go on to, and scratch dig into, the case so that will be grounded and there we have one that hasn’t changed that’s what we’re expecting a good Alternator. And then if we switch these around do the same again there we are, I don’t know if you can see that…. So, it should be between about five hundred and eight hundred (millivolts) That’s around 470 so that should be fine we’re testing the diodes there so it doesn’t appear as though we’ve got any diodes that have ‘gone’ (burnt out) from this test. I’ve hooked up a battery from a drill here so I’m now supplying 11 volts to the alternator and this is a full field test – I’m checking to see if it generates with some voltage applied there …and it doesn’t, so we are now going to have to move on to the disassembly and see if we can find a problem in there. Before we start to disassemble this, we want to make sure it goes back in the same orientation so just to mark that out… [Scratches alternator case to form witness marks] I know that looks awful doesn’t it but it’s quick and no about of cleaning can remove those marks so I know it’s gonna go back the same way it came off. These bolts are 8 millimeters [unscrews retaining bolts] I’m just giving these a gentle tap with a hammer just to get them started and then afterwards I can wedge it apart with a flat blade screwdriver. There we go – that’s it started. Ok, the rotor came out with a little bit of gentle persuasion I got a flat blade [screwdriver] and I was just against here because I thought somebody was going to say ‘don’t hit the lugs – you’re going to crack the lugs!’ But then I wasn’t recording anyway! The [front] bearing is in really good condition. The slip rings are in excellent condition, much better than I had imagined actually, and I’ve measured the resistance of the armature winding on this rotor and it’s about 3 Ohms, which is good and there’s nothing immediately wrong with this part of the alternator so I’m now having to dismantle – because I have also looked into the stator here and the brushes are in good condition, nice and long and there is no evidence of overheating here really – yeah, there’s nothing completely obvious. So I’m afraid i’m just going to keep dismantling – take off the ‘oily part’ as well and get out the electronics, so that I can test things properly. No doubt you know this already but just in case somebody doesn’t.. This fastener here is ridiculously tight… I’ve been trying to undo it ther with a flat blade [screwdriver] and it’s just not working. So a little trick: just get that nice and centred. Lump hammer: [bang] Give it a good whack, and then try again. There she goes… I’ve got these three fasteners out now… Make sure they are the same length… yeah. Ok I’m now going to remove my little oil pump… or vacuum pump… oil driven vacuum pump! (Third time lucky…) and now I can access some more fasteners and get this little bad boy apart! The nuts on the back of this are 8 mm on this Bosch Alternator. And I’ll just just undo these, and try to get some more access. Thes nuts have got little captive washers with them. And it looks as though this is going to have to come off as well, the stud [nut]. Gentlemen! And potentially a few ladies I suppose as well sorry – I don’t mean to be sexist… I think I may have found a problem I’m in the process of removing the stator armature [winding] form the aluminium housing, and before we go any further I just wanted to show you the problem. If I wobble this around this is going to one of the windings and that should be connected here electrically and mechanically and it’s not. So, I believe this is our problem. I’m about to split the stator here the stator armature from the aluminium housing and actually everything’s gonna come out together – the electronics all come out together, and the studs as well, come through the body and all out as one assembly. I just wanted to show you – It didn’t look as though this was going to be easy to split but then I just found now, sneakily hidden there is a small gap and you can get screwdriver into there and that should help me to start prizing this apart. There she comes… There we are so it allcomes out in one go. Now we can get a good look at what is wrong with this. Here we see what this assembly should look like. The windings from the stator are soldered here and then these, in turn, are soldered to the rectifier and control assembly there. So if I wobble that around you can see that this is all moves together. However, if we come over this side this should be the same but – hopefully you can see this – it’s not. So we have some solder broken there. So of course there’s no electrical connection or mechanical connection here and the same has happened under here: This should be soldered onto the base plate below it – or above it as we are looking at it now – but it’s not! I’m now going to snip the attachment here and here. I’ll come back to you in a minute… I need two hands. There we go that’s this one done. So, I’ll do the second one now and then that will release this is. I’ve got these all snipped now… I’m just going to withdraw… Ther we are. Now we’ve got this separated we get a really good view of the rectifier and regulator assembly and this is most definitely our problem… As let’s started to work loose, it will have started to arc and overheated: hence the melted plastic that we can see just here, so this is kaput! There we are then we found our fault! Now the good news is I’ve been online and you can buy these separately so you can buy just the diode plate here and that costs around 25 dollars or you can buy this entire assembly and that’s about fifty dollars so you may be able to spend $25 to fix your alternator, instead of $350 to buy a new one… If you wanted to replace this entire component, it is really easy: You just place it back into position like so and then you crimp over the tabs and you get some high temperature solder AKA silver solder… 1,2,3,4 dabs… There you go that’s ready to go back together and then once you’ve completed a successful bench test and you know it working again you can fit it to your car and you’ve got the car back! I’ll leave some links in the description of the video to that the parts i mentioned this is a Bosch alternator but by looking at these parts you can get an idea of the kind of parts that you might need for yours and no doubt they will sell them for your alternator too. Thanks for joining me guys, I hope you enjoyed this video and I hope something useful came of it I’m sure something useful it will come from the comments below: We’ve got a good community going here guys and you always come up with some great comments so I’m looking forward to reading them when you ‘make’ them. That’s it, until next time, don’t forget love life!

About the Author: Michael Flood


  1. Before i replace my alternator what should else should i check? im thinking my cheap battery might have killed the one I have but it has had 190,000 through it.

  2. شــُـكـرً لــّـك
    Chris :
    ،Thank you very much
    Very Excellent Lesson.
    Keep Up.
    I benefited very much from your instructions,
    so thank you again and again.
    I’m very grateful for you
    An Arab, Engineer.

  3. Would it be possible for him to go further? Instead of buying that part could he just solder the wire that was disconnected?

  4. Mrs. E here, Thank you! My Dad left me an amazing shop and tools, so there are ladies in the audience. You help me carry on the DIY spirit. A firm Texas handshake to you!

  5. hey Chris, I hope you see this soon, I have a 2007 Honda Pilot, and the continuity test is good, as well as the reverse one where you switch the test leads…. however when I do the test where you put a screw driver, the alternator pulley does not move on either direction, aka locked up. I opened it up and checked the brushes and the copper rod where you were checking resistance and it is good too, only problem is that it is locked up with the screwdriver inside, with no screwdriver it is very smooth in both directions. the pulley doesn't look sophisticated and I am wondering how it works on this car, or what could be wrong. any help appreciated

  6. Great vid. Very informative. I used to just get a new alternator, now, I'm going to save some money! Thank you very very much!

  7. Thanks a bunch. I was looking for how to open mine and see the problem, already got a replacement (used) but started making a humming noise and stalling/ dragging the engin when idle.

  8. Thank you so much I just replaced my alternator myself, I didn't even think of repairing the old one I gave it in for a core. I think the problem inside mine was the clutch from the loud squeal I smell I was experiencing. "subscribing"!

  9. Good info Chris. During the first part of the video the alternator was off screen. I would like to suggest using a tripod instead of a camera mounted to your head. Thanks.

  10. Chris, My restoration has stalled as I cannot even take the four long screws out that holds the alternator together.

  11. bloody good, mate! starters, alternators are very easy to repair. but. i think they intimidate somewhat. I had one i repaired for two dollars one time. all it needed was the brush end, bearing. wholesale distributor right up the street. only two dollars. wallah!

  12. Chris, in your opinion, is an oem remanufactured alternator worth buying over a new oem one for replacement on a 98 honda accord with 110000 miles on it? Thanks in advance!

  13. I have an 83 diesel ranger with the same oil pump on the back of the alternator. Will this be the same taking apart/fixing as this one? Also if anybody has a diesel ranger out there with some tips let me know please!

  14. Great vid , great step by step and easy to understand , but at the end of the day , the bone yard has a pile of good ones for 40 bucks each.

  15. Ive been working on my 1995 fiat barchetta over the winter. I had the battery removed and after charging and connecting before i even turned the ignition on, smoke puffed up from alternator area. Now battery light will not go off on dash !
    I can only think that some fluid has dripped down into it and caused problem.
    Do u have any idea if its a simple fix or a new alt ??

  16. Could you help me with an issue I have on my 1997 Fiat Ducato Alternator, it's a MAGNETI MARELLI, my van is a motorhome. The reading at the starter battery was 13.28V and roughly the same on the habitation battery, with the engine running at idle. I tried disconnecting the leisure battery and voltage went up a bit to 13.49V, I have checked all the wiring, also done a voltage drop, checked the earths etc. Took a reading with my multimeter directly from the alternator with engine running and got the same reading 13.49V. Nothing like 14V which I was expecting. Is this a fault with the VR??

  17. I love videos like this I stupidly left my rav4 into Toyota to get a new throttle body sensor fitted they charged me €300 euros for the sensor I coulda got it online for $25 dollars and they charged me €300 euros to fit it my own mechanic woulda charged me €45 the job was that easy I coulda done it myself!! very well informed video!

  18. can you make a video showing what they do with the old alternator you give for a core refund? What causes them to go bad? Why do alternators have brushes? Ac motors are brush less and can generate ac power.

  19. great tutorial thankyou. I'm not a mechanic but dad was a royal engineer and I'm a scientific engineer but love my project cars.

  20. I am curious, couldn't you have just resoldered the original part without replacement? Thanks

  21. same problem as mine, i ordered an entire assembly to replace" no doubt your a good mechanic sir!

  22. I didn't know that Rodney from Only fools and horses has knowledge of alternator repair!Good work man!I'm bug fan of Only fools and horses but this channel is also cool!

  23. Just ordered a brand new alternator for my F150. But I think I'll keep the old one and try this rebuild. It might come in handy if/when this new one ever goes out

  24. Hey Chris, nice video. I'm an amateur mechanic but a professional electronic technician. As such it was a nice tip you mentioned silver solder.

    But out of curiosity, was it not possible for you to make a mechanical connection and then solder those wires down yourself onto what was left of the original diode assembly?

  25. awesome. gave me hope. I can not find a alternator for my car any where looked and looked so great video.

  26. Thanks for the dismantle that alternator , have you ever thought about doing a video on producing AC power out the back of the alternator from beginning to end connecting the three wires to the stater out the back cover hooking up the few transformers you need from what I can figure out 12V to 240V out of each wire off the stater you have 110 AC volts three wires what I can see 330 V AC power into transformers connected to easy generator plug into your home fuse box ! Back up power in case of electrical failure in what I see they say out of each alternator out the back is 90 Amps , 2 Alternators = about 600W @ 180 Amps – off you’re electrical company they provide 250W @ 240 Amps

  27. I have not seen anyone rebuild an alternator since the mid 70's. Didn't know you could even get the parts. Thanks.

  28. Good video, real mechanics fix parts such as alternators, they don't exchange them for a dubiously rebuilt one at a car parts store.

  29. Wtf why are these things built so cheap, broken solder points? This is in a moving vehicle. You should be able to roll the thing down a large hill and have it work fine afterwards.

  30. Hey Chris,great video,I just subscribed,my local electric repair shop used to rebuild the alternator's,but now say to just through away and buy a new one,I believe he don't make enough money with it ,so they just tell me that,not doing me any service? What do you say?Where do I get parts to do the job my self? Thanks

  31. Great job I'm looking through the web to see if I can find one of a MKX Lincoln alternator but it'd be the same or similar to it?

  32. You do have females watching love well done catching and correcting yourself, my mothers a Mechanical Engineer who is designing off shore wind turbines and I'm here learning how to fix my jeep cheers for the content magical being. X

  33. Just done mine the bushes were covered in crap cleaned them off and wiped the copper junctions down touchwood it's OK. But taking it off I now have a slight leak of power steering fluid bloody Citroën Berlingo

  34. Pretty cool, but for most cars you can pick up a used working alternator for not much more than the parts cost to repair it so not really worth it unless you have a rare type of alternator that’s expensive to replace

  35. Excellent excellent video Chris. I wanted to check that I had done my alternator rebuild correctly. The only bits I didn't properly check were the resistances with my meter. Unfortunately it's now back in the car. My only feedback is that the video was a wee bit blury when you were showing where the solder was meant to be. That was all. Again, Excellent video.

  36. My car's battery dosen't charge while engine is started and head lights on,on other time when i turn off the head lights and accelerate the engine,then the battery is charging.this issue only comes while lights are on…can you explain this to me,why this is a toyota corolla dx wagon…

  37. Outstanding work! Not only well-videographed, with good audio and lighting, but the narration is smooth and the information beyond compare. I subscribed immediately.

  38. Thank you for the video. Finally someone who repairs the problem instead of replacing the entire alternator. Great work and very detailed instructions. Saved $300 US.

  39. اصلان کارت قشنگ نیست..اشتباه باز کردی..فولکش میخاد..دینام خراب میکنی. عزیزام .بلد نیست ی نکن.مرسی.

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