On the way to get my wagon inspected yesterday and it dies while at a red light....Long story short, I get it running today with a jump start from my wife's vehicle and check the voltage at the battery with my VOM and it starts off at 13.52 at idle and slowly started going down by .01 about every minute, after that I hold the RPM's at 1500 and it lingers around 13.46 -13.47 and stayed like that for the 5 minutes I held it there, Finally I let it go back to idle and almost immediately it starts going down by .01 but a bit fast than before. At this point I decided to call it quits and went over to turn off my jumper car and walk back to the Mercedes (5 feet to and back) and as I am approaching it the idle starts getting erratic (slowing/surging) so I quick put the VOM on it and it was all over the place 13.30,12.72,13.18,11.97,12.48 and did this for about a minute (maybe a bit less) and shut it off.

I got some advice but that was on a lot less information than what I gave here. I thought it was the Alternator and this person said to check out the Voltage Regulator first because most of the time it is a voltage regulator issue and not the alternator. Now up until my testing the voltage at the battery with it running I just did a lot of reading (A LOT OF READING) and it seems that people had issues with bad grounds, shorting wires, and a couple of other things that I cannot remember.
I am hoping some of you guys after reading this have an idea of where to start......To me it is still a voltage regulator and maybe an alternator issue, I am thinking of just buying an 80A version and fix to problems at once. If there is anything else that could be causing voltage drop and then the erratic voltage later on please let me know.

You can get a generic voltage regulator at your local auto parts store for under $25. All it takes is two phillips screws to remove it, and it pops in.

If that doesn't do it, look at replacing the alt.

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

dka-66, remove the voltage regulator and inspect the length of the brushes. It's likely that they're worn to short stubs. If so, recommend replacing with a new Bosch voltage regulator.

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Fred Hoelzle

I am about to go help a neighbor move his garage stuff to his new home but I will check as soon as I get back. Thank you for the info.

I do see one on autozone.com but it is says it is for an 80A alternator. Autozone Voltage Regulator Will this work just to get it going and then I can buy a german one.

that's the one....it should work as well as any other

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

my 80 Amp alternator had a slow voltage drop after 10 to 20 minutes of running . This with a freshly replaced regulator unit .
The fault was isolated to one diode which was effected by heat soak .Diode pack replaced and normal charging of around 13.9V now

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mark

Diode pack....they sell just the diodes?

Just got the voltage regulator out and snapped some pics....Is this considered a worn voltage regulator?

[IMG][/IMG]
[IMG][/IMG]

I would say this is worn or borderline worn

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

Just wanted to thank everyone for their help, It looks like the new voltage regulator is working..and now having said that I fully expect that something will go drastically (and expensively) wrong.

On start up the voltage at the battery reads 14.05 and after the rpm's drop it seems to be staying in the 13.76 to 13.83 region with no load.

I would be budgeting an entirely new alternator within the next 10,000 miles. From your pictures it looks like one of the brushes is shorter than the other by a fair amount. This is because the contact ring that they ride along inside the alternator is worn. The new brushes will wear just like the ones you took out. Soon you will be going through voltage regulators every couple months. (Spoken from experience)

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

I noticed that and figured no good could come of it. Thank you for pointing it out and letting me know what would happen.

I was planning to upgrade the alternator to an 80A model by using the wiring harness from a 91 or 92 300E (I think that is right)......Is there an easy swap like this for one of the 90A alternators?
When ordering my voltage regulator from discount auto (just wanted to get something fast to see if it really was the VA) anyway, I saw an 80A Alternator that they are selling and was wondering if anyone had experiences with the chain store aftermarket parts?

Also, with the aftermarket 80A from Discount Auto it looked like it had two studs on the back so I am assuming someone who upgraded through that route would have to cut the connector off of the MB harness and crimp some new connectors on.....Is there anything wrong with doing it this way, I was thinking off getting something that can handle a new head unit and a couple amplifiers....maybe three if I try to fit a sub in somewhere.
So could I take any high quality high amperage alternator and use it.

I just do not want to keep buying alternators every time I decide to change something and would like to know what my options are.

All 300E's had 65amp alternators I believe. A few months back I installed a 120amp alternator from an S320, and it dropped in with no issues. Just had to swap pulleys from the old alternator. Used stock wiring connectors (although I will upgrade to larger gauge wiring at a later date). They also make a 150a alternator in the same housing.

http://www.peachparts.com/shopforum/showthread.php?t=53236&highlight=alternator+upgrade

Here is a thread with more info on that upgrade. It's a good one!

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

dka-66, the brushes are far from worn out. I replace the voltage regulator when the brushes are 3/8" to 1/2" long. Therefore no need to replace your voltage regulator. The wear is typically greater on one brush so that's no cause for alarm.

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Fred Hoelzle