*Edit for the person viewing this thread in 20 years. Are flying cars as cool as we thought they'd be? Anyway, my problem turned out to be a fried voltage regulator*


Hello all,

I haven't been able to find my issue via search, so here are my symptoms:

-My 1982 300D is charging the battery fine, but while driving the climate control fan ramps up and down erratically (not clicking like normal automatic climate control).
-At night, my headlights also flicker slightly.
-At startup, the battery and brake lights stay illuminated until I give it a little bit of throttle, then they go away.
-I bought one of those cigarette lighter voltmeters and it corresponds with the climate control fan ramping up and down. This confirms that power is surging, and is affected by RPMs (although not mirroring RPMs directly).

About 4k miles ago I had the original alternator rebuilt and replaced the voltage regulator. I just pulled the voltage regulator and it looks fine, no abnormal wear.
My belt is pretty tight and still in good shape.

So here are my theories:
-My Hella voltage regulator is of poor quality and already going bad.
-The alternator is worn out
-the belt is slipping

Thoughts?
Thanks in advance.

What did the slip ring on the alternator look like.

There is an AC voltage test (not DC voltage) that you can do to see if there is an issue with diodes inside of the alternator. I can't remember the details but perhaps someone will chime in.

If you are in good with a mechanic they could hook the alternator up to the engine analyzer and it would show what used to be an oscilloscope pic of the alternator output and it would show up a bad diode.

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84 300D, 82 Volvo 244Gl Diesel

Thanks Diesel911, the slip ring looked ok. Not brand new, but no grooving or excessive dirt. I don't have a shop that could do this for me, is this similar to the test that auto parts stores do?

Subscribed to learn.....

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I am not sure what the test at say Autozone. I took an Alternator to Autozone and they said it failed the test. I took the same alternator to Pepboys and it also failed there but Pepboys gave me a small print out on what might have been wrong inside. I got the impression that Pepboys had a more detailed tester compared to the one at Autozone.

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84 300D, 82 Volvo 244Gl Diesel

From my notes:

AC voltage across battery
VAC across battery should be under 100 mV; excess AC voltage on the DC line means one or more of the rectifier diodes in the bridge are leaking or shorted. Such a problem is relatively rare but unfortunately means replacing the entire alternator.

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84 300D, 82 Volvo 244Gl Diesel

Thank you for the follow up, I am going to see if I can check that myself with a multimeter.
A dead alt. isn't the end of the world, I was looking to do some sort of upgrade eventually anyway.
Anyone have a plug and play alternator upgrade suggestion? I've seen folks mention the Saab upgrade, but those don't seem to be as plentiful anymore.

http://www.peachparts.com/shopforum/diesel-discussion/364297-diy-al129x-alternator-1978-w116-300sd.html

The AL129X Bosch alternator is still available, go with new vs. used to avoid issues.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Thanks Alex, I was just looking at that write-up you wrote a few years back. My hesitation is that apparently the AC compressor manifold hose blocks the electrical plug on that alternator.

When you say go with new vs. old, how do you feel about remans?
It's looking like $171 for reman vs. $240 for brand new.

Thanks again.

Look on eBay. Someone sells 80-90 amp alternators that I believe still can use the regular alternator connector.

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84 300D, 82 Volvo 244Gl Diesel

This is the eBay sellers titles:
120 AMP Mercedes Alternator High Output Generator 230 240 280 300 450

$143.54 + $14.95 shipping In the picture it shows it is setup for the stock connector but it only has a single groove pulley. So you would need to swap the pulley. There is a application lists in the sellers text.

This same seller may also sell on Amazon

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84 300D, 82 Volvo 244Gl Diesel

Bless you. This is perfect. 120amp on stock connectors, that's great. Once year warranty is nice too.
Thank you! If I end up replacing the alt, I'll probably order one of these and swap the pulley. Not an issue.

I used a rebuilt by BOSCH unit that came from Germany.
To my mind, remanufacured by BOSCH is as good as new by BOSCH.

In my write up, I forgot to include that I had clocked the alternator halves on the AL129X by 90 degrees so as to match the terminal positions to the wiring harness.
There wasn't enough slack in the wiring harness to reach the terminals otherwise.
The AL129X should (hopefully) clear your AC compressor manifold hose if you clock the alternator halves.

Back view of Stock AL129X

Old alternator and clocked, rebuilt AL129X alternator

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

When I went to replace a bearing on my Alternator which had a sticker Bosch America on it I found that it had Chinese Bearings inside.

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84 300D, 82 Volvo 244Gl Diesel

Thank you Diesel911 and Alec, you are very helpful.
Alec, when you clocked it, is it just those two screws on the case or is it more involved than that?

I also come back with more data and findings, after a long drive:

At high RPMs/freeway speeds, the system is fairly stable between 13.0 and 13.5v, no matter what accessories being used.

At low speeds, however, it bounces around between 12.9v and even 15v. Then, the lights will also *sometimes* flicker rhythmically. Lastly, as I pulled into the driveway the battery light on the dash started to flicker rhythmically (this is new).

I'm pretty much condemning the alternator at this point. But, before I do. Is it even remotely possible this could be a belt issue? I'd hate to throw some parts at it and find it's really just a belt.