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!

100 thoughts on “How to Repair Your Own Alternator (With Simple Tools)”

  1. William Cormier III says:

    thank you very much, you saved me about 225 dollars (us)

  2. Willie Fufu says:

    It was good to watch your Video and learn that I don't have to take it to Autozone as a core, when I buy another one. This is empowering.

  3. Valentin Ioniță says:

    Thank you! Your video really helped me. It is a good video with all details we need.

  4. LL YNWA says:

    I don't know if its quite related but my tachometer for a diesel engine keeps as if vibrating at the zero mark when accelerating.. From the news i have read… It works together with the alternator… Any idea of the problem?

  5. Michael Lawson says:

    Pretty cool video!

  6. SV Zaya says:

    When the alt fails the diode test. and it was only producing 0.1 volts less than the battery running. My problem is that its a Westerbeke engine (Perkins 4108) and they want US$138 for the diode part. I dont know the OEM manufacturer of the alternator (possibly Mitsubishi), is there some way of identifying/replacing the diodes, avoiding Westerbekes prices ???
    cheers man

  7. donnyboy says:

    Thank you very much… Well said and well done.!

  8. pedro velazquez says:

    Hello and many thanks chris for this straight forward video. I have a question rather than a comment . Would the overheated plate that turned out to be the problem in your case ,be the cause of the alternator clutch wheel to fail ?

  9. Broken Motor Wagen says:

    I think the part where you hooked up a battery would have been the most useful part of the video if you went into detail.

  10. Jiwbink w says:

    NEW SUB!!!

  11. Mike Higgins says:

    I have a 1985 Austin Maestro 1.3 HL is the alternator easy to repair?

  12. solar energy says:


    Its amazing

  13. mdrnawy Dernawi says:

    How to test regolater?

  14. Jay M says:

    learned quite a bit, thanks for sharing your knowledge.

  15. Lebron Jordan says:

    Great info 👍!

  16. Lena James says:

    Thanks for including the ladies! ❤ .. Have done this once before, may have to again on another alternator. Love how you say aluminum 😍

  17. Joshua Christensen says:

    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.

  18. M AAR says:

    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.

  19. Renate Lewis says:

    I don't even know what you talking about.

  20. Jason McKenzie says:

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

  21. Benjamin Benjabliss says:

    How do I get those repair parts online? I need it in good quantities

  22. earl McDaniel says:

    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!

  23. Incony Blue says:

    excellent video.. ty.

  24. Fresh Vids says:

    Is every car alternator has the same problem like this also?

  25. B G says:

    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

  26. Marcin Otocki says:

    This tutorial is brilliant ! Best regards from Poland

  27. Jim Bronson says:

    No one but me can see my comment but good video bud.

  28. Jake Smith says:

    Too tedious; I just let warranty give me a new one

  29. BigFoot Too says:

    I can't stand dirty and greasy parts. I alway clean the up before and during repair.

  30. Michael Pierre says:

    thanks chris, you learn something new everyday.

  31. angkeltat says:

    I enjoyed ur video. Thnx chris.

  32. Jack Sorroche says:

    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!

  33. kens Vintage Toys says:

    Very good video, you sound like your from the UK

  34. Chris Owen says:

    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.

  35. Sondra L says:

    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"!

  36. Gary Langley says:

    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.

  37. Jason Junsay says:

    very helpful!

  38. ernest lee morell sr says:

    … Thanks for the info, I am pretty sure that I will be able to get it done before 2030 👎👈👉??

  39. MsCelicagt4 says:

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

  40. paul joe says:

    Awesome vid. You did a great job. Mate.

  41. Arthur Bradley says:

    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!

  42. living in a desert says:

    Do we stop for tea?

  43. Pat Rick says:

    awesome explainer vid!

  44. Darren Dixon says:

    Low reading from the bridge rectifier ie diode pack .360

  45. Dora Dean says:

    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!

  46. H Mac says:

    Nice work, thanks for sharing

  47. Sarah Alvarez says:


  48. Suavecito Soto says:

    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!

  49. Meesho Batayeh says:

    Awesome man thank you

  50. Johnny Vee says:

    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.

  51. arnietwo says:

    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 ??

  52. Ronnie Pirtle Jr says:

    I haven't been able to find an alternator kit in 20 years!
    I used to rebuild mine all the time.

  53. Rebekah Hendle says:

    Thanks mate great video. Very descriptive innit

  54. Paul Outten says:

    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??

  55. Chevy Van Travel says:

    why white paper?

  56. Serval Ferré Traficanté says:

    Thank you very much

  57. Little Reptilian says:

    What's an oil driven vacuum pump for the servo? Why oil driven?

  58. Lawrence Van Niekerk says:

    A wood saw 😂😂

  59. owen shannon says:

    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!

  60. Living the God life says:

    Awesome 😀

  61. Tau Ugava says:

    Thank you chris…excellent video

  62. chriss4365 says:

    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.

  63. Lazar Lazar says:

    Thanks , I am now an expert on alternators !

  64. Bold Creator says:

    Why not use newspapers on the table!? It's cheaper and thoose white papers are sliding around!

  65. Fire Links says:

    Wats the name of the parts them

  66. Ed Williams says:

    Thanks, but loose that British accent . Just kidding cheers .

  67. sashanesterov says:

    It is very encouraging in our time, that so many people still have hands and brains!

  68. Thomas Owens says:

    Why the white paper

  69. Paul Castro says:

    Thanks for posting it. The whole procedure is a full learning experience.

  70. Lucas Membrane says:

    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.

  71. Steve Roffey says:

    its hitachi not bosch.

  72. Effendi says:

    Great video mate! Thank you

  73. Jake Salisbury says:

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

  74. chukchee says:

    Wouldn't it be easier to buy a new one with lifetime warranty?

  75. RANDOM LIFE says:

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

  76. Nick Mick says:

    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!

  77. MikeDaTiger says:

    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

  78. blah says:

    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?

  79. Mark Almeida says:

    Big thank you Chris!!!!

  80. Joanne Philip says:

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

  81. Mark Sanders says:

    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

  82. shajahan legal says:

    more tutorial videos! plz.Thank you very much dear!!

  83. Lamster66 says:

    Got to get mine off this weekend not charging but also making noise like bad bearings

  84. jim noyb says:

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

  85. Robin Sattahip says:

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

  86. Pixelated Mushroom says:

    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.

  87. Randy Thompson says:

    Wow, you just made my day.
    Thank you from Pensacola, Florida, for your knowledge.
    New subscriber here.

  88. my 2 cents says:

    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

  89. David Perez says:

    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?

  90. T R says:

    Good job awesome 👍👌

  91. Fivas says:

    Kaput 😂

  92. Days Eye says:

    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

  93. Sam S says:

    Dude. Nice video! Subscribed!

  94. winandre says:

    Good video

  95. Rocky fish says:

    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

  96. Christian Pusey says:


  97. Ski Lawd says:

    very good video thanks

  98. Val Bigfish says:

    Vacuum pump on the back, thats off a diesel i bet!!!

  99. Nitro says:

    This is the best video so far. Extremely complete instructions and great camera angles. Cheers!

  100. Xhar Suarez says:


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