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Old 08-04-2004, 10:42 AM
R Leo's Avatar
Join Date: Mar 2003
Location: En te l'eau Rant
Posts: 5,373
Voltage Regulator/Alternator Trouble

I am in power generation h*ll.

About two months ago, Marlene's alternator failed while we were in OKC forcing us to travel home ohne Komfort. I didn't mess with it until after we returned from our big vacation, putting it off until about two weeks ago. I quickly installed a rebuild from a local rebuilder and went on my merry way until two days ago when I got in the car to run an errand and all the lights on the dash stayed on after the engine was started.


I determined that there wasn't any juice going to the battery so I pulled the voltage regulator and look at what I found!

One of the brushes was misaligned on the commutator and wore sufficiently in 1000 miles of use to create this nib. I guess it then wouldn't make contact and generate current.

I installed a spare VR I had and am back on the road, for the time being. I'm going to pull this one in a week or so to inspect for unusual wear. More details then.
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Old 08-04-2004, 10:54 AM
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Join Date: Apr 2000
Location: So. Cal
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Check out the commutator plate. Possible that it is scored or otherwise worn and was not replaced during the rebuild. That could possibly accelerate the wear on your brushes.
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

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Old 08-04-2004, 11:00 AM
R Leo's Avatar
Join Date: Mar 2003
Location: En te l'eau Rant
Posts: 5,373
Yeah, I also thought that seemed like a lot of wear for 1k miles. When I had the VR out, I looked at the commutator and it to me seems too rough. Commutator rings should be really smooth, IIRC.

I'll run it like this for a week or so, pull it and inspect. If I see wear, I'll pull the whole unit and return to the mfgr.
Never a dull moment at Berry Hill Farm.

Last edited by R Leo; 08-04-2004 at 11:59 AM.
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Old 08-04-2004, 11:30 AM
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Yes, from my experience you are both right on the money. Once the slipring surface on the rotor gets too worn, it gets difficult to get the brushes to work out well.

I remember several years ago, benzmac posted that he would replace the VR the first time the brushes wore out, but could rarely successfully reuse the alternator after the second VR wore out. He also, if I recall correctly, said that he would replace the alternator if the brush groove was deeper than an 1/8".

Good luck,
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