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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!

Bernard Jenkins

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