Was well into a long drive yesterday when I noticed my battery light pulsating. I had about an hour of day light left, so pulled off the highway and had the alternator tested.

According to their machine, the regulator failed.
Fortunately, I was traveling with a spare. Installed, retested and back on the road. About an hour later, I noticed the flickering again...

Turned off all the accessories and reached my destination.
Battery was at 12.18 this morning. Just enough juice to start the car...
Connected my multimeter to the terminals and drove around town for a while keeping a weather eye on the voltage. It jumped around a bit, though hard to know what's normal

Rolled into a parts store and had them test the alternator and battery. Battery is old, but checked out. Alternator regulator failed.
Charging voltage during test was around 13.19 average.


1.) Plan this afternoon is to clean the ground strap (from trans bell housing to chassis)

2.) Clean the battery terminals

3.) Clean the alternator harness/plug

4.) Check belt tension (changed belt about a year ago, doesn't sound like it's slipping).


Am I missing anything?
Does this sound like a bad alternator?
Or something else?

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1981 240D 4sp manual. Ivory White.

look for a german made regulator, china made suck like uro parts

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Noted -regulator brand is a hella.

Performed steps 1-4, charging voltage measured at battery terminals is now holding at around 13.75v

Found the retaining clip for the alternator harness was not fastened. Possible the harness came a little loose. Are these alternator tests worth anything?

Suppose I won’t know if this fixed the issue until I’m on the highway again.

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1981 240D 4sp manual. Ivory White.

I had a (cheap) huco regulator that did that. Defective

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1985 300TD 1981 Scirocco 1.6D conv 1986 Golf 1.6D 2003 Golf TDI

The attached pic is of a contact point that can be seen inside of the Alternator after you remove the voltage regulator. The one in the pic is obviously corroded.

One side of the voltage regulator makes contact with the alternator housing so that area of the housing needs to have good contact.

What did the slip ring the brushes ride on inside of the alternator look like?

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Thanks for that 911 -that’s one contact point I failed to consider.
I also didn’t get my head in to there to have a look at the slip ring.
Will do both this morning.

It is it normal behavior to occasionally need to blip the throttle before the alternator kicks in?
Noticed this while taking voltage readings.

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1981 240D 4sp manual. Ivory White.

It never has been that way with mine and that is since 2007. Is the engine idling with in the speed on the emission sticker/tag? The tag on mine has750 plus or minus 50 but on an older Engine 700 rpms may be too low and 800-25 may be needed.

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84 300D, 82 Volvo 244Gl Diesel

Ya, someone was having trouble with is alternator and posted that pic along with some others and I could not believe that it was possible for something to corrode inside like that.

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84 300D, 82 Volvo 244Gl Diesel

When replacing the regulator take a few minutes to check the surface of the slip rings. If there's a carbon build up on the rings, it will perform just as if the regulator was bad. You can clean the rings by wrapping a piece of abrasive cloth around your finger tip and reaching through the regulator opening. Turn the pulley by hand to polish the rings all around.

Since two regulators had the same result, we'll assume for now it's not the regulator. But the blip the throttle thing means there's high resistance somewhere in the regulator circuit. It could be brushes/slip rings, the D+ connections, or the ground that 911 pointed out. The reason this happens is that bootstrap voltage is normally lower than 12V, because the bulb is in series with the regulator. So the output voltage ramps up for a "soft start." The bulb will only go out when D+ is balanced by generated voltage, which takes a little time. But this is normally too quick to notice. If you're starting with unusually low bootstrap voltage due to high resistance somewhere, then you can't overcome D+ until the engine really revs up.

Great question.

Sadly, I do not own a photo/Tac, nor does anyone else I know.
The final time I paid someone to do a valve adjustment for me and pore over the car for any maintenance items I may have neglected, the idle was bumped a hair. The "reading" mind you, was taken by ear. Mechanic ears, not my ears.
This was a couple years ago.

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1981 240D 4sp manual. Ivory White.

Fantastic response, thank you.

Since cleaning the ground strap and alternator harness/plug ends, the charging voltage has returned to 13.8, so that's a good sign.
In addition to the internal ground, I'll take a light to the slip rings before the day is over and give them a quick buffing.

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1981 240D 4sp manual. Ivory White.

I am spoiled as 300Ds have a tachometer. Perhaps you can just raise the idle speed a little and see if it solves the issue.

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84 300D, 82 Volvo 244Gl Diesel

Well, I wire brushed the additional ground that connects the voltage regulator but couldn't get to the slip rings without removing the alternator. Photo below before brushing.



Drove back to O'reilly's and this time the alternator passed their battery of tests.
Even the voltage regulator.

Definitely requires a blip of the throttle to read, however. When they connected the test machine it said something like, "make sure engine is running." I blipped the throttle stop and everything whirred into action. Once that's done, it settles back into an idle and works perfectly.

Seems intuitive, but is there a bedding in period for new brushes?

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1981 240D 4sp manual. Ivory White.

The brushes will wear into the grooves on the slip ring. I blew up part of your pic trying to get a better view or the slip rings. They clearly have wear.

The contact fingers were clearly corroded. Unfortunately oxidation does not usually conduct electricity well.

Bosch type alternators are so prolific that they sell new slip rings you can remove the old and solder in a new one. I don't know where you would take one to have the slip ring turned down.

I have a Lathe but have only turned down a slip ring 2 times in 42 years.

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84 300D, 82 Volvo 244Gl Diesel

The rings definitely show wear, but whether they are “worn” I can’t say...
I was able to clean up the contact fingers pretty well, however.

This is bringing back shades of my failed starter rebuild.
Bought all the major refresh elements, and the issue ended up being something minor (part not available).

Have you performed this job? Has anyone else other than Stretch?

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1981 240D 4sp manual. Ivory White.