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Old 06-24-2002, 04:15 PM
Former Dieselholic
Join Date: Feb 2002
Location: West Michigan
Posts: 380
went through 2 batteries, when the alternator got hot it shorted out and just killed the battery in about 30 sec.
Just curious...
When the alternator "shorts out" is it gone for good? Or does it come back with a charge to the battery?

I ask because I am having same symptoms with my 1981 300tdt.
I checked the voltage with a charged battery and 12.5 idling, revving, all lights and accessories on: No change.
The guy said that the alternator is probably shot. I removed the Voltage Regulator and the brushes are about 3/4"-1" long. And evenly wore, shiny at the ends. I assume this is good.

THEN, I found loose wires at the alternator and pos. terminal of battery. "Fixed" them with no positive results.

Hmmm...I guess I have to bite the bullet and replace the alternator.
(Someone please jump in and stop me b4 I actually begin to change it out... )
Current: '91 300TE 4MATIC 317k and climbing...
'81 300TD Wagon 168K "Tank"
'83 240D 216K 4spd manual "Da Bear" (aka best car ever)

"Never sweat the petty things...
and never pet the sweaty things."
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Old 06-24-2002, 08:00 PM
Posts: n/a
Gilly, if I had a lift, installation would have been no problem. Since I was crawlling underneath the car, I had to install it with one hand, and since the brushes are spring loaded, it was frustrating.

Diesel, to correct my quote, after further investigation, the alternator did not short out, instead the voltage regulator became so worn that when the car was hot, charging would halt.

Your brushes seem to have plenty of meat on them, unlike mine, see above. When you put the regulator back, is it snug? At the very least you can try putting a new regulator in there and see what happens, ~ $35. At the very least you can return it if no change.

IF that does not work, you have time, you can purchase a remanufactured alternator for on the web for ~ $150. or less? just my 2 cents.
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Old 06-25-2002, 11:07 PM
Posts: n/a
I was talking to someone today and he said that the type of alternator that I have in my 1990 with the voltage regulator with the brushes has been discontinued for many years.

Is that true? If so, what is the technology of alternators past that era and today?
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Old 06-26-2002, 08:34 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Only the construction and performance has changed. Various engine management systems have taken over the output control but the mechanism of control is still varying the field current.

My Bosch rep told me of the newest alternators that should be coming out in the 42 volt systems. They use the cars flywheel as the rotating field and can be rereverse wound (or controlled) to make them into starters. The point being to allow cars engines to stop at idle and then be smoothly brought to speed with magnetism.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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