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Lucas Alternator Rebuild
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Sun Mar 23, 2008 9:09 pm    Post subject: Lucas Alternator Rebuild Reply with quote

Last year the stag’s alternator packed up, it s a Lucas ACR, as fitted to thousands of cars from the 60’s through to the 90’s, I fitted another alternator at the time but today rebuilt the faulty one. Thought this post may be useful to others and save you a few bob.

First of all I put the alternator in the cleaning tank to get rid of what turned out to be 32 years of grease and grunge!


You can purchase a repair kit for the Lucas ACR alternator for about £12 the bits are in the pic blow, its well worth it unless you just need to change the brushes. Worn or damaged brushes account for most alternator failures and only cost a couple of quid, this is where the recon trade make its money! To rebuild an alternator with all the bits in the kit will take about an hour, if you only need to change the brushes it is a 5 min job once the alternator is out of the car.


So in the pic from left to right t you get;

• A set of brushes
• Slip Ring
• Voltage regulator
• Rectifier (converts the AC an alternator produces to DC)
• And the 2 alternator bearings



Tools required are, a ¼ “socket. 5/16” socket, & a 6BA socket, if the rectifier or slip ring need changing, a 40Watt soldering iron.

First of all remove the plastic cover.



The screws for the brushes can now be seen these are the 6ba jobbies, and you can take the brushes out by remover the 2 screws per brush. If the brushes are worn or damaged then replacing them will probably bring your alternator back to life.

On removing mine it was very evident what the problem was, the carbon brush was detached from the copper wire.



Replacing the just brushes would have got the unit working , but as I had a kit of parts I wanted to do a puka job, the bearings were a little noisy so at a minimum these would be replaced.

The slip ring is a visual check, either the copper may be worn or like mine the plastic was beginning to break up (would not stop it working,but as I had one this would be replaced). You will need at least a 40Watt soldering iron to heat up the copper lugs, tin it first with a pool of solder, and the add the 2 rotor wires in.
The slip rings are keyed so you can’t fit the incorrectly, and will have some form of spring clip to hold it in place.



You can check the rectifier with any ohm meter, there are 9 diodes which will conduct with the meter one way round and not conduct with the meter the other way round, takes a couple of mins to do the test, you could be really unlucky that a diode is failing under load, but this simple check will cover 99% of faults. If there is a problem you need to un-solder the 3 wires from the rotor and re-solder on to the new rectifier.

The voltage regulator is more difficult to check, my advice would be to change it if everything else appears ok.

There are 2 coils in the alternator one on the stator which has the 3 wires which go to the rectifier, if you put an ohm meter between any of these 3 wire it should read like a short circuit, they very rarely fail and if do so physical damage is normally visible.

The rotor coil can be measure from the slip ring, and will be about 5 ohms; you can of course measure through the brushes where it could be up to 10 ohms.

I should add that it is really rare to get a coil failure, and if you do either ditch or exchange the alternator.

The shaft and outer bearing can removed simply by placing in a vice, putting the nut back on and tapping out with a hammer.





The bearing on the end of the rotor can be a pig to remove (see above) , it has a plastic insulator behind it and there is not enough space to get a puller, I use this method;
Because bearing case is hard steel, if you put it in a vice and tighten the vice up, the case will easily crack. Then do the same with the inner part. Not probably best workshop practice, but it works without damaging anything else, you may want to put a heavy cloth over it as you tighten the vice up, below is the old bearing ; (do this with the slip ring removed befor putting in the vice !!!)



After that it’s a case of bolting the alternator all back together, total time to rebuild about an hour from start to finish, only difference from an exchange unit is that , a) you know what has ben replaced (and your echange unit may only have new brushes!!) and b) exchange units will be cleaned up beter and repainted.

If anyone wants brushes for a Lucas ACR unit I have a load of them; 99p a pair including postage.

Dave


Last edited by ukdave2002 on Wed Mar 26, 2008 1:35 pm; edited 6 times in total
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Rick
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Joined: 27 Apr 2005
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PostPosted: Sun Mar 23, 2008 9:31 pm    Post subject: Reply with quote

Great write-up there ukd, thanks for posting it!!! Smile

Rick
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Uncle Joe
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PostPosted: Sun Mar 23, 2008 10:27 pm    Post subject: Reply with quote

Excellent write up UK, even I managed to understand it! Laughing

I have a faint memory that Lucas changed the wiring on later alternators as well, didnt they? European termination or something if I remember?????
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SloResto



Joined: 17 Feb 2008
Posts: 36

PostPosted: Mon Mar 24, 2008 8:18 am    Post subject: Reply with quote

Thanks for a most informative post UK. Apart from my usual hassle with alternators my Volvo 240 recently experienced something strange with its starter motor.

I had repalced the starter motor a few years back so wasn't expecting any trouble.. at least nt for a while.

Suddenly it wouldn't crank - so tightened all the wiring and try to crank - again and again to no avail.. battery OK etc

Then when I had a closer look at the starter body I noticed that it had loosened and was coming apart. The two long skinny through bolts that actually hold the various stages of the starter casing together had somehow worked loose... and had sheared the earth strap in two.

I couldn't get the starter to bolt up together so luckily had a spare on hand which I swung over and was back on the road again in a couple of days (gulp).

As you say auto electricians are making a killing on "reconditioning" alternators. two years back i dropped mine off at a garage to get repaired and I nearly fell over when the workshop manager went to charge me $280. (Australian dollars)

I could not believe the price and told him that I could buy a new Alternator for $300 and that I had some work done on it 2 years previously where the mechanic had to remove it and reinstall it from the car and only charged me $140.

I actually removed it from the car - cleaned it up and they still wanted to sting me $280. I told them to forget it and I went and bought a second hand one form the breakers for $80.
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pigtin



Joined: 23 Nov 2007
Posts: 1879
Location: Herne Bay

PostPosted: Mon Mar 24, 2008 12:36 pm    Post subject: Reply with quote

First class write-up. I have spent much of my life associated with the repair of fractional horsepower motors and know the theory of of generators etc' but have never looked inside a car alternator. I know what to expect now. Many thanks. Very Happy

Don.
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ukdave2002



Joined: 23 Nov 2007
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Location: South Cheshire

PostPosted: Tue Mar 25, 2008 9:58 am    Post subject: Reply with quote

Uncle Joe wrote:
Excellent write up UK, even I managed to understand it! Laughing

I have a faint memory that Lucas changed the wiring on later alternators as well, didnt they? European termination or something if I remember?????


Hi UJ

There were quite a few changes to vehicle alternators in the 60, the early ones had external voltage regulators, some needed a 12V supply to “excite” the field windings, (on these if even you managed to start a car with a flat battery the alternator could struggle to develop current to charge the battery).

By the early 70’s alternators all had built in regulators, with electronic voltage sensing, and were self exited. I have read reports of mechanics in the 70’s swapping an old alternator for a more modern replacement, which only has about half the number of external connections, getting the wiring wrong and then not being able to turn an engine off because the new “self exited” alternator was providing 12V to the coil side of the ignition switch!.

The European connecter you refer to only has 3 spade connectors and 2 of them are joined together! (The larger 2), the smaller one being the connection to the ignition warning lamp.

Was this a common termination adopted by alternator manufacturers?
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Uncle Joe
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PostPosted: Tue Mar 25, 2008 11:02 am    Post subject: Reply with quote

UK, I'm really testing my memory on this one, so if I'm wrong, apologies.

Way back in the early 70's, I had an ex-Chrysler Competitiions H120. This was really good a blowing alternators. The final one that I fitted was this ''European termination'' type. If my memory is correct, it had an internal rectifier, and replaced one that didnt. My memory is that at least one wire was not connected to anything, and two were, as you say, connected together.

There was a wiring change to US Chrysler alternators, but I dont think this was for reasons of unreliability. I could check to see if I have noted anything though. As regards Bosch units, havent a clue...

Perhaps Ricky426 can answer this as regards italian electrics?
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REG



Joined: 21 Mar 2011
Posts: 2

PostPosted: Fri Sep 30, 2011 6:32 pm    Post subject: Re: Lucas Alternator Rebuild Reply with quote

ukdave2002 wrote:
First of all I put the alternator in the cleaning tank


Quote:
If anyone wants brushes for a Lucas ACR unit I have a load of them; 99p a pair including postage.

Dave


Dave

EXCELLENT article, gave me the confidence to take mine apart before sending for 'refurb'.

1. What's the 'bath' please? I have my alternator apart and wouldn't mind giving as good a clean as I could.

2. Do you have any brushed left - I can't find any for sale anywhere near that price!

Best wishes

REG
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ukdave2002



Joined: 23 Nov 2007
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PostPosted: Wed Oct 19, 2011 2:56 pm    Post subject: Reply with quote

Hi Reg

The solution was machine marts general purpose cleaner. If you PM me with your details I'll sort some brushes out.

Dave
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JohnDale



Joined: 19 Mar 2008
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Location: Kelvin Valley,Scotland

PostPosted: Wed Dec 28, 2011 12:25 pm    Post subject: Reply with quote

Good, well written post Dave, plus good good pics. The reason for the two terminals being connected was when replacing alternators from 35amp 17ACR etc to the greater outputs,45 amp & above, the terminals could take the increased amperage but the wiring couldn't, so an additional cable could be fitted(but very often wasn't) Low battery,max charge, melted wiring. All made work for the working man to do,cheers,JD.
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MikeEdwards



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PostPosted: Fri Apr 08, 2022 6:22 pm    Post subject: Reply with quote

Sorry for resurrecting this old topic, but I have a related question.

I've had a dim warning light on the dash on and off, and the battery gauge only just stays into the good half when the engine is running. I thought I'd remove and strip the alternator, which is pretty clean to look at both inside and out, and the brushes are good.

The two main parts of the alternator - the part that spins (the 'stator'?) and the part it spins inside (the 'commutator'?) are both quite rusty. I've cleaned up the spinning part using the wire brush on my bench grinder. But how much cleaning can I do on the outer part?

Is it safe to get some wet and dry and clean the "pads" on that outer piece until all the rust has gone, and they're back to clean bright metal? I've started doing that, but I thought it might be a good idea to ask before I go any further in case there's some sort of protective coating on them that I shouldn't disturb.
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MikeEdwards



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PostPosted: Sun Apr 10, 2022 6:32 pm    Post subject: Reply with quote

I've given this a clean up now, having read on various sites that fine paper is OK to use. I've also got a soft wire brush for my dremel-a-like which cleaned it up well.

I've put it back together, it seemed to be running well and producing around 14.5v, then after 30-45 seconds it drops to around 12.8 and the warning light is back on, dimly. Sometimes if I leave it running it will pick up again, but then drop again.

This is the trace on the Crypton, which isn't as nice and even as the one in the manual:



Any ideas on what might be causing this issue? The brushes look almost new, the whole thing is very clean inside other than the bits of rust that I mentioned above.

I should probably add that this is a Delco alternator, so all the stuff is inside it. The one I'm working on is actually marked Lucas LRA130.
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petelang



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PostPosted: Sun Apr 10, 2022 8:56 pm    Post subject: Reply with quote

I'd suspect regulator problem. If you can bridge return path of field to ground (shorting out regulator) and it charges again I would suggest a new reg. If not, something must be wrong with the rotor field circuit or brushes. Brush could be sticking or dodgy Slip ring solder? Some have a shorting thermistor diode if overheat occurs and this could be shorting your field circuit?
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MikeEdwards



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PostPosted: Mon Apr 11, 2022 8:56 am    Post subject: Reply with quote

Thanks for that, I'll go away and read up on it. I'm reasonably sure that the brushes aren't sticking - they seem quite happy to pop out of the holder as soon as I remove the centre rotating part. Presuming you mean physically sticking so as to not make decent contact.
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MikeEdwards



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PostPosted: Wed Apr 13, 2022 6:28 pm    Post subject: Reply with quote

As you suggested Pete, the culprit was the regulator. I didn't do any of the testing you described, mainly because it's not something I know how to do. I had another alternator, and in turn I swapped the diode trio, then the rectifier, and finally the regulator, swapping each part back when it proved to make no difference. As it's an unknown alternator, I wasn't sure what was good and what was bad.

Why did I do the regulator last? Because I didn't make a note of what you said, so I just thought I'd work through the three parts in turn.

The Crypton scope display is still the same, so that maybe points to an issue with the Crypton rather than the alternator. It's outputting up to 15v (and sometimes up to 15.2v) so it does at least look as if the charging is OK.

Someone on another forum posted that the trace should be basically flat, as the alternator should be outputting DC. Given that the manual has a similar shape to the trace that I photographed, why would that be?
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