A couple days ago when I went to start the '82 300D Turbo the battery light didn't turn off as soon as the engine started. It turned off after a few seconds. Later on in the day when I started the car and it didn't turn off at all. Next time I went to start the car I got the classic dead battery sound. Since the battery is only a year old I went to the store it was bought and they tested it. It failed the test so they gave me a free replacement because it was under 18 months old. I put in the new battery and now the battery light doesn't come on instantly but slowly gets brighter and stays on after you turn on the car. Also brake pad and park brake lights don't turn on with the key in the second position like they should. I thought maybe the battery was a little low on power from sitting on the store self so I drove the car around for 20 minutes hoping to recharge it a little. They battery light stayed on the whole time. So I don't know was the battery dying just a coincidence? I'm thinking the alternator is going south or maybe there's a short somewhere. So what do the diesel experts think?

Check the brushes in the alternator. They are in the removeabe holder in the alternator. Alternator usually doesn't have to be remover to get the holder out. I replaced the brushes in my 300SD over 100,000 miles ago and they are still working. They only cost a couple of bucks and are much easier to replace than than changing the alternator.

P E H

TXBILL,

Yes, it is a great idea and it might work. SO: Why not try the easiest and most economical fix first? If that doesn't work, then I might consider replacing the alternator.

P E H

Well I followed the procedure in the Haynes manual, and the battery is not getting the volts it should. It's a little lower at idle then when turned off, but it should be a couple volts higher. So either the alternator is not producing the power or it's not getting to the battery. Is there any way to rule out that the voltage regulator without replacing it with a new one?

From the description removing the alternator doesn't seem that hard. Loosen 2 bolts, move it around a little, and unplug the wires going to it. Is it much harder or very time consuming in reality? Is tightening the dual belts running the alternator a pain after re-installation? Thanks for the replies and keep them coming.

You can have your alternator checked for free either in the car or on the bench at most parts stores (Auto Zone, Advance Auto Parts, etc.). Replacing the voltage regulator is a cheap fix that can last for many miles or very few miles, but worth a try if the bench test does not show a bad diode or other component. I replaced my voltage regulator once and it lasted about 12 months. If you buy a voltage regulator and it does not work - you're stuck with it as most parts stores will not refund your money.

Before working on the alternator disconnect the battery negative terminal to prevent an accidental short. I have to jack my 300D up a bit to get enough room to access the alternator, but I have worked on it without jacking the front end up. You want the belts snug, but not too tight because too tight can ruin the bearings. Your Haynes manual should have good info about R&R'ing the alternator.

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
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Supervisor of Maintenance largest tree care co. in US for offices in Tex.

Wow that was quick, Tom. I'm planning on cleaning or replacing the brushes and if you can remove them without removing the alternator, well that's great. So if that doesn't work I'll try the voltage regulator. I'll take advantage of the free electrical testing if the brushes and voltage regulator course of action is a failure.

I should have mentioned this before but the first thing to do is a visual inspection of the brushes to see if they are worn to a point where they don't contact the slip rings on the alternator.

If the brushes don't contact the slip rings, new brushes will probably solve the problem. If the brushes do contact the slip rings, the problem is something else and replacing the brushes will not not solve the problem. I don't remember the brushes being that hard to replace but if I remember correctly, a soldering iron is required.

Sure you could replace the alternator because it has bad brushes but that's like replacing the engine because it has bad injectors. That will work to solve the problem but it isn't the easiest or most economical solution.

P E H

This may be a long shot, but check the ground for the negative cable from the battery? If this was really bad though, I don't think it would crank to start, hmmm.

I would go with the worn brushes. Makes sense the way you described the light-first started flickering, then staying on would mimic the wearing of the brushes lifting off of the rings.

Yup.

__________________
Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"

Crazy thing about the way the alternator light works is that if the brushes wear out and that causes the alternator not to work, the indicator light will not illuminate. Therefore if you determine that the alternator isn't generating electrical current and the alternator light isn't illuminated, it is probably bad brushes.

This is a design error in my opinion. When my brushes wore out I was on the middle of Alaska with a dead battery. I didn't know the alternator wasn't working for the reason above. Luckily someone came along and gave me a jump start to get going. Being a Diesel, it would run with a dead battery, just wouldn't start by itself. I made it all the way home to PA without the alternator working by charging the battery every night and just driving during the day.

P E H

PEH

That is a fantastic story! All the way to PA????

About the brushes not illuminating the light, doesn't seem logical does it.

I had this same thing happen to me, stranded in a strip-mall. I had no clue the alt didn't work. Fortunately I got help from the buxom bartender at the local bar in the strip-mall and got home. She jumped me with her new Z-28. Jump-started that is.
Checked the charging at the battery, nada. Put in a junk alt purchased at the local pick and pull for $10, and voila!

Thanks for reminding me about this odd failure mode.

To all of you out there, if you notice the starter doesn't turn as fast, or your lights seem dimmer, check your voltage!

If you don't have a meter, go to Radio Shack and buy one, Do it today!

__________________
Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"

I forgot to ask how to gain access to the brushes. Are they behind the black plastic panel on the back of the alternator? Also the alternator adjustment bold has a like a metal rod connected or touching the side of the bolt. So I can't get the socket over it, and a regular wrench won't work at that angle. Do you need a special tool for this or something? Thanks for all the replies!

240ED.

YEP, all the way back from Alaska about 6000 miles. The only place I had trouble was in Billings MT because I got there late and the headlights looked like candles because the battery was almost dead. This was 10 years ago and I hadn't had the car too long so I didn't know much about it and there wasn't any Mercedesshop web site then to ask. As you can probably tell, I don't like to have anyone else work on my car, I'd rather do it myself.

Had I known about the brushes in the alternator I could have fixed them on the road. When I got home I took the brush holder out and was able to get the alternator to work by resoldering the brushes to make them able to extend slightly farther so they would make contact with the slip rings. This was just temporary fix until I installed the new brushes and they have been working ever since. I do expect I will need another set of brushes soon, though because this was 100,000+ miles ago.

Do you remember the commercials by Chrysler when they first came out with alternators about 1959? They took the battery out of a car and drove it all around the USA. Of course they never shut the engine off. The idea was to show that an alternator put out enough voltage at idleing to keep the car running. This is because of the rotating field in an alternator can be driven at a higher speed than a generator armature. Thus the alternator will put out higher voltage because it is driven faster than a generator. Ever notice how small the drive pully is on an alternator compared to a generator?



P E H

MR123.

Yes, the brushes are in the holder that is in the back of the alternator. The cable pulls out after you move the wire clip that secures the cable to the alternator. Remove 2 screws and you can remove the combination brush holder and voltage regulator. This is a neat design that makes it very easy to replace the brushes or voltage regulator without removing the alternator from the car.

I don't know what model MB you have but the adjusting screw is hard to get at on my 116 also. I think I used a 10mm combination wrench that could be turned only thru a small angle so it takes a lot of small turns.

P E H

Mr.W123,

I have changed the brushes and Voltage regulator on W123 Diesels a number of times, and I had the same indications you describe. In fact, if you are driving at night and the typical W123 dash lighting syndrome leaves you with a dimly lit instrument panel, you can see the battery light glowing a deep, dark red before it actually fully lights up. Turning off the head lights makes it go out, but leaves you driving in the dark. Anyway, I have always seen the dash light give me the warning that the alternator was not producing the necessary Voltage to charge the battery, just not always burning brightly, especially when the car is using some of the electrical power in the battery and there is relatively little Voltage left to light the instruments, and warning lamps.

There is a little spring clip over the back of the connector to the Voltage regulator that you push off and then unplug the wires going to the battery/electrical system. Then there are two screws holding the Voltage regulator to the alternator, that also hold the assembly in a position to compress the springs that keep the brushes (little quarter inch or so square cross section graphite rods about two inches or so long when they are new, and about an eigth of an inch long when they are shot) in contact with the rotor of the alternator. As I recall the contact was not with a typical smooth slip ring, but with copper bars embedded in the shaft which can get burrs and things on them that grind the brushes away quickly.

Anyway, you unscrew the two screws and the assembly is loose. You tip is slightly and the assembly comes out of the back of the alternator in your hand. If the brushes are little short things, they are shot. You should look at them to see if they have gouges or other signs of bearing on a rough surface, as the new ones will wear out shortly if that is the case. If one brush is significantly shorter than the other, this is an indication of potential mechanical and electrical unbalance in the machine. If there is any indication of roughess on the rotor contacts, or unbalanced mechanical or electrical performance, you should change out the alternator, or you will be chasing this issue over and over.

A new Voltage regulator assembly typically used to cost under $20, and the alternator rebuild was $65 to $120, depending on where you got it or had it done. So the temptation to just address the Voltage regulator and brushes (a half hour job at most) should be resisted if there is reason to believe the machine has other problems. On the other hand, I have had the Voltage regulator change work for 3 or 4 years, and 75k miles when all that was wrong was the two brushes just wore down and no longer made good, continuous contact.

Getting the alternator out is not difficult, but you have to make sure you are turning the correct screws. I have not done this in quite a while, and would suggest you check out a manual. I know I have bent up the adjustment rod and bracket doing this job before, and made things unnecessarily difficult by being thick headed and proceeding without a manual.

Good luck, 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)

Whew, I thought I was the only one who bent that rod:p
Solution of course, is to loosen the pivot bolt, etc.

There were two designs of alt brackets, one with a toothed bracket and special bolt, and the familiar infinitely adjustable, funny looking adjuster nut thingy. You can go to a yard and grab whichever alternator you want, with either bracket, and the alternators are the same.

If you can find a small rebuilder like the one in my town,( San Jose Generator- on San Jose Ave.) you are in luck as these people are great! They will put in new bearings, rewind the armature, or whatever. Like new.

Just forget Kragens!!!! They guarentee them for life, but you have to keep changing them out every 6 months!!!

__________________
Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"