Joined: 23 Nov 2007 Posts: 1725 Location: South Cheshire
Posted: Sun Mar 23, 2008 9:09 pm Post subject: Lucas Alternator Rebuild
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.
Last edited by ukdave2002 on Wed Mar 26, 2008 1:35 pm; edited 6 times in total
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.
Joined: 23 Nov 2007 Posts: 1815 Location: Herne Bay
Posted: Mon Mar 24, 2008 12:36 pm Post subject:
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.
Joined: 23 Nov 2007 Posts: 1725 Location: South Cheshire
Posted: Tue Mar 25, 2008 9:58 am Post subject:
Uncle Joe wrote:
Excellent write up UK, even I managed to understand it!
I have a faint memory that Lucas changed the wiring on later alternators as well, didnt they? European termination or something if I remember?????
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?
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?
Joined: 19 Mar 2008 Posts: 300 Location: Kelvin Valley,Scotland
Posted: Wed Dec 28, 2011 12:25 pm Post subject:
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. _________________ Use 'em or lose 'em.
1960 Ford Zephyr.
1968 Triumph 2000.
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