Lucas 18ACR rebuild

Tom W

Active Member
#1
I decided to give my alternator a mild refresh as I’d experienced some intermittent charging in the past. I found when I stripped it down to investigate, that the brushes and slip rings were slightly worn, so I ordered some spares and decided to rebuild.

The original brushes looked identical to each other. The replacements (NOS genuine Lucas with a red label) have one tag with a terminal on it. I fitted this brush closer to the regulator, as the other has the corner chamfered off, which matches the brush carrier moulding. Does anyone know what this terminal is for? I thought it might be something to do with the battery voltage sensing wire, but it doesn’t line up with the hole for that. My cars never had the sensing wire connected, as the alternator fitted is internally sensed. There’s also a surge protection device mentioned in the manual that isn’t in my alternator. Confusing!

Anyway, the ammeter is showing a healthy charge after the rebuild, so that’s all good. It would be nice to get the battery sensing circuit to work properly though. Partly so there’s something to connect the sensing wire too, rather than leaving it taped up, and mostly because I think sensing the battery directly is better on a system where the battery is in the boot, and could experience a voltage drop.

5435C945-8C6F-4D65-B0ED-AD1AADA3645C.jpeg
 

roverp480

Active Member
#2
A battery sensed alternator will have a white lead from the regulator unit to the sensing terminal & the control unit in your picture has not got one so I believe it is a machine sensed with no battery sensing facility.
 

Tom W

Active Member
#3
Yes, my guess if it’s not the original alternator, but a period replacement. The regulator is a genuine Lucas one, so I’ll not be swapping that out for an unknown quality modern version whilst it’s still working.

There’s a sticker on the side of the side of the alternator that says DRA1691. When I search for this online, it brings up a Delco Remy 29amp alternator. The original should be 45amp. Everything on this alternator is branded Lucas, apart from this sticker!
 

roverp480

Active Member
#4
I seem to remember that LUCAS developed a rationalization replacement policy of supplying Machine Sensed alternators for service as they could replace battery sensed ones but not the other way round . Lucas agents didn't then have to carry so much stock.
 
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