Hi all,

First post in a while here - been busy and the car has been running great Sorry for the newbieish question but I cant find an answer in the archives.

85 300D

Battery Light is on at idle, goes away at speed.

Have not had a chance to check charging voltage yet. Battery less than year old, alternator ~50k old.

Voltage regulator suspect, right?

thanks,
dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Check the "exciting wire" The small guy that plugs into the alternator. The stock alt needs to either be fed 12v to excite the field, or you need to spin it up above 2,500. If you can get it to kick in my revving in neutral after start, and it stays active, that's your culprit.

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

Second option would be worn brushes.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I'm with jeremy, check your brushes -easy fix! My car did the exact same thing, do it before its too late - don't ask how I know this -

How does the belt look?

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Jim

experienced this on a VW diesel once, culprit was worn out brushes.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

thanks guys for the replies -

I will check the belt and make sure it's turning. Belts are maybe 30k old and keep them in good shape.

Will also check the brushes. This would be the third regulator this Bosch rebuilt alternator has eaten in 50k.

__________________
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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Hey all,

Replaced the voltage regulator, but one of the screws that held the regulator in was frozen and snapped. Grr. So only one bolt holding regulator in.

With regulator held by my finger the charge voltage goes up to about 13.0V as measured at the battery terminals. (not the 14V ish Im used to seeing).

Does this indicate a new alternator? (Battery is good - takes and holds charge fine)

Let me know how to definitively see if the alternator is dead. Ideas on how to get the other bolt out without removing the alternator also welcomed :-)

Thanks,
dd

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

One of the diodes on the alternators diode board has failed, not an expensive part but a hassle to fix if you haven't done it before.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

If it's coming out anyways I guess Ill put a new Bosch back in. This is one of the few parts that can stop these cars quickly with no preventative measure to use against it :-)

for future readers who with to become diode replacers, is there a tutorial somewhere?

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-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

i couldn't find an exciting wire on my schematic, is this a real thing? i liked that explanation the best of all, but never heard of this part.