1981 300D

Hi Guys,

This morning I started the car and it cranked very slowly. Since the charging light disappeared as soon as the engine started (the bulb is OK) I thought it was the battery so I went to SEARS to have it checked. The guy tested it and concluded it was bad. They put a new die-hard on and I drove away.

A few miles later I realized that he didn't check the charging system. I stopped at a gas station and checked the voltage with my multimeter. With the engine running the voltage was 12.43 volts...and with the engine off it is 12.43 volts!!! On top of that, the headlight's intesity is constant regardless of engine RPM.

Is the voltage supposed to be (engine running) close to 14 volts, isn't it? This is my first diesel so I don't know the exact voltage.

If the alternator is bad, why does the charging light on the dash board is turned off as soon as the engine runs?

Thanks for any input

Kefer,

You probably need a good diagnostic check of the alternator/voltage regulator. The battery should last a reasonable time unless the charging system is flawed or there is an interior or trunk light on all the time, and you have a constant drain on the battery.

Your intuition about the voltage with the car idling and no electrically powered equipment on, is correct. You should be around 13.6 to 13.8 Volts. With a full load (lights, high beams, fogs, fans, A/C, rear defroster, etc. on) the Voltage should be above 12 Volts. If not there is a problem with the alternator/voltage regulator. If you have never changed the brushes in the alternator, that may be the cause. They come as a module with the Voltage regulator (~$40), and are easier to change that way. Others on this site have managed to just replace the brushes for a couple bucks total. The replacement of the brushes is a little tricky as they are retained in the regulator housing against little springs that push them out toward the rings of the alternator rotor. The Voltage regulator assembly is on the back side of the alternator, and has some wires plugged into it, the plug is held in place by a little spring clip you push off to remove. Then you take two screws out of the corners of the Voltage regulator, then it kind of tips and rolls out. If the brushes are less than half an inch long, they are getting worn down to the edge of reliability and should be replaced. If they are unevenly worn, it is an indication of mechanical and electrical unbalance in the alternator and you need to have the alternator rebuilt. My inclination would be to get a rebuilt one from Fastlane.

Hope this helps. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Thanks Jim.

I'll check the brushes tomorrow. I'm pissed at SEARS for not following through and just selling batteries without a proper check. I've had good experiences in the past with them.

Do you have any suggestions on how I should handle a possible refund since the other battery I think it's ok, just discharged?? The previous owner bought it 18 months ago or so...it's an AC Delco. I assumed that brand didn't last as long as the die-hards.

I think the alternator hasn't been touched since the car left the factory in Germany. It's an 1981 with "just" 150,000 miles.

I'll post the results. Thank you.

Kefer,

I have had good luck with the local Sears, especially the battery guys. Did you have them check the original battery first? They usually do a check of the electrolyte to assess the health of the battery. Diesels can "deep discharge" a regular car battery a few times in relatively short order if the weather is cold and especially if the alternator is not working well. That can ruin a battery, making a replacement necessary long before the design life of the battery is reached.

So, you may actually have needed a new battery, but it is unlike a decent shop to take the car in, find a bad battery, and not check the charging system out. Another issue with the brushes wearing out is before they are really shot, they only do not work intermittently. And the normal Sears or other shop check of the alternator/voltage regulator is pretty straight forward and lasts a few minutes. Maybe your alternator seemed ok then, or if the results were borderline and because a fix was beyond their scope, they were reluctant to tell you the alternator was weak or bad without some real convincing evidence.

These Diesels are not every shop's forte, and you get used to confronting inexperience over time. Which is why this forum is such a great resource. Hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I got the brushes out of the alternator. Piece of cake, but I think putting them back in will be a challenge.

One of them sticks about 1/4" out of its casing and the other 5/16". I think they're worn out. I found 2 long brushes that I will transplant.

I'd like to know how much should a new set of brushes "stick out" of their casings to be electrically sound yet easy to install in the alternator?

Thanks.

Kefer,

I would agree the brushes seem, by your description,to be shot. They should stick out all the way, except for the feature that retains them. There are little springs under them that push them out and against the alternator rotor contact rings. When you put them "back in" the alternator they should be part of the Voltage regulator assembly. You kind of feed them back in the hole in the back of the alternator in the extended position, and then as you roll the Voltage regulator back into position to put the screws back in, you will feel them being pushed back into the Voltage regulator, against the springs. Just make sure not to force anything, and make the initial fit up using your hands, not by just drawing up the screws. Once you have the Voltage regulator in position, flush against the alternator, run the screws just about all the way in by hand. Then tighten them, and plug the wire back in, making sure the spring clip is positioned to over the back of the plug.

Just replacing the brushes is technically all you probably need to do. It is a little tricky though as you have to "transplant" the mechanism that retains the brushes in the holders against the springs, and I do not know how that is done. I have saved my old Voltage regulators thinking I would do this someday, but never did. I just bought a new regulator.

Hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Having just gone through this mess, I sense that Jim is right on in his advice. The length of your brushes sound similar to where mine were.

It was kind of tricky getting the volt. regulator back in but after a few tries it kind of found its home. Instantly kicked the volts back to 13.8

Let's hope that is the problem.

Don

__________________
DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed

Yes, I'm sure your problem is alternator related and if the rotor is in good shape a new brush set will most likely fix it.

The reason your dash light did not come on is that it relies on the brushes for a circuit. Go figure!

Good luck,

Charging indicator is a design defect. The brushes must be good for the indicator light to come on. So if the brushes wear out and the alternator doesn't work, the indicator light will not light.

I found this out in the middle of Alaska, but made it home to PA without replacing the brushes until I got home by charging the battery every night. Nice feature of a Diesel, it doesn't need electrical power to run after it is started, except for the new CDIs.

P E H

Where can you buy the brushes? Do they have a specific part number\manufacturer - so I can locate them here in Canada?


Aivars

1981 300D

I put new brushes last night. The old were sticking out probaly 1/4 of an inch; the new ones I let them out maybe 3/4 of an inch or so.

I bougth a GM alternator repair kit for 13.99 and just used the brushes. I'm in Boca Raton, Florida and it was impossible to find a pair of brushes alone.

I installed the regulator this morning...it actually was very easy (which made me nervous thinking I had done something wrong).

I turned on the engine and now the voltage is 13.6 volts @ 2000 rpm. without any electrical load. With the headlights on it's about 12.93 volts.

What do you guys think of these numbers? Am I home free?

Thanks

Kefer,

I would have expected the 13.6 to 13.8 V reading at idle (2000 rpm is a little high for idle). But it sounds like it is much improved and I would hate to alarm you as the repair was probably successful. A temporarily slightly low Voltage reading may be due to the condition of the battery if it was discharged and is now returning to a normal charge state. I expect you will be ok. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I measured the voltage again this morning and it was 13.7 volts @ idle. I think it's fixed for good!!

Thanks guys.

You might also pull the connector on top of alternator and clean it with elec contact cleaner and then a shot of wd40. I went from 13.8 to 14.2 by doing this. 14.2 is the spec output for my alternator.