Hello,

I have an '83 300SD and am having a problem I hope someone can help with..

About three weeks ago, my battery light started flickering on at times. It happened mostly with all the electrical accessories running (headlights, heater fan, etc.) and when at idle for a while in traffic. Once I started moving, the light would go off and not come on until I stopped again. All of my lights, including headlights, would dim at the traffic lights. If I touched the accelerator even a bit, they would brighten up.

About a week or two ago, the alternator belt started "chirping" at idle. I tightened it a bit and it went away.

Last night, things got weird. My lights started dimming and eventually went out. The car ran fine (being a diesel..) but I was without radio, lights, etc. I drove home and parked. The car is now completely dead.

My question is this: battery or alternator? I can't figure out if my alternator is fine but the battery won't hold a charge -OR- is my battery ok and the alternator won't charge it?

I am not sure of a lot of the service history of this car, but know the battery is 2-3 years old (I was getting ready to change it..) and the alternator looks like it was replaced at one time (not sure how old, but it looks newer than 1983).

Any thoughts?? I bought this car as a 'beater' and it's become our everyday car, for long trips and everything. I'm back to driving my 'good' car which I now hate... Weird, huh? :)

Neal

First check the alternator(ALT)brushes. You should be able to get them out without taking the ALT off. They can be taken out by removing some screws holding the brush holder. If I remember right the holder is the part that the ALT cable is connected to. Remove the cable first.

I think I hold some kind of unofficial record: I drove all the way back from Alaska to PA in a 300SD without the alternator working. I thought the ALT was bad and I didn't want to pay a fortune on the road for a new one. Actually it was just the brushes. If I would have known at the time how easy they are to fix, I would have put in new ones on the way home.
P E H

TXBill,

I don't remember the charge light coming on much last night. It might have flickered at idle.

Once all of the lights began dimming (and I figured out there was a problem..) the red light didn't come on solidly at all. I actually don't remember seeing during the 5 minutes or so while the lights were dimming and dying out.

I'd like to take a look at the brushes, but what am I looking for? Should I maybe take the cheap way out and replace both the brushes and battery (since I'm sure both of them will need to be replaced sometime soon anyway..)?

Do the brushes come as one unit and are they part of the cover I'll be removing when I take out the screws? Or am I pulling the cover off the back of the alternator and getting the brushes out from inside it?

Neal

I think the brushes come out with the cover. You can tell if they are worn out, the carbon will be very short, maybe 1/8".
My light never came on. I think I remember a post that said the indicator light goes thru the brushes and doesn't work if brushes are worn out. Sounds like a stupid design, especially for MB. When I was in Alaska, I didn't know the battery was dead until electrical accessories stopped working, but engine kept going fine.
I wouldn't replace the battery if the ALT brushes fix the problem. It probably is OK. If the ALT isn't working, even a new battery will go dead. You aren't replacing the tires and eventually they will be need to be replaced but not now.
If it ain't broke, don't fix it.
P E H

My vote is alternator given that everything is dead now. I had a parts shop test my alternator and ended up putting in 3 batteries thinking alt was ok and their batteries were defective when in fact it needed new brushes. It sounds like you drove home on battery power.

Good luck.

Neal,
The brushes are attached to the cover.
Simply remove the two screws and remove the old set, then pop in the new one, and replace the screws. It is about a 5 minute job.:)

Brushes are about $40, while a re-man Bosch starts at $80. Most alternators are good for two sets of brushes, so it may be better to get an alternator.

I new battery would be a good idea if the old one is more than 3 years old.

Good Luck with it.

I would check the brushes first. 2 minute job. They are held on the back of the alternator by 2 screws.they are part of the voltage regulator which is a black round object.The brushes can be change seperately without spending the bucks for the whole unit. If that does not work the battery may be the problem. I have had batteries do weird stuff.

I don't think the brushes are $40. They are a rather simple part. Seems like I paid about $5 some years ago. Check the price from parts shop.
P E H

The brushes are a part of the voltage regulator:hence the $40-$50 price.Brushes cost maybe $4or$5. I always replace the regulator and don't have to mess around removing and replacing brushes.I have seen a few alternators, that would check good, but the connecting plug would be corroded. This plug can be bought from a MB dealer. It's not too expensive.
So, check the connections at the alternators.
Bill Lewallen

Thanks for your help guys...

I managed to get a new regulator and tried to remove the old one. Got one screw out, but head of the other one(the one close to the block) is now stripped.

It's too cold out now.. I'm going to take it in and have someone pull the alternator and swap regulators for me. Hope this fixes it!

Neal

i have a simailar problem with my 84 300d.
with all the electric accesories on the charging voltage falls to 12v.
i removed the brushes and they are like new.
i think the problem is that some of the diodes in the alternator are bad.
i will wait for the summer to remove the alternator to check them.
remember that dep cycle batteries require to be charged quickly and at high voltage to last long....
would appreciate any input from more knowledgeble sources
thanks

bhatt,

Did you get your problem fixed? I am having the exact same problem in my 420SEL today. Did new brushes with a voltage relay fix it, or did you need a whole new alternator?

I just called the local parts department and they said a rebuilt exchange alternator will cost me $437. I can get the brushes and voltage regulator for $67.30.

420SEL,

You need to put in an inquiry with the Parts Shop. I'm quite sure they can get you a Bosch authorized rebuild for MUCH less. Don't waste your money on auto supply alternators, unless they happen to be Bosch authorized.

Everyone,

There is a simple way to see if the alternator is working. Measure the voltage across the battery with engine off, it should be somewhere around 12 Volts. Then, measure the voltage across the battery with engine running, it should be somewhere around 13.5 to 14 Volts. If the voltage stays near what it was without engine running, the alternator is not charging.

You can take most any battery to Sears and they will test it for you. Of course, if it's bad they will expect you to buy a battery from them, but they're not going to shoot you, or hold your battery ransom if you don't. They have a machine that will check it in a matter of minutes.

Good luck,

420SEL,

I couldn't get the voltage regulator/brushes out since one screw was stripped. I had a shop do the swap instead. They had to remove the alternator to swap the brushes.

The shop left the car out overnight to see if it would start in the morning. Wouldn't you know it.. dead the next morning! They put a new battery in and everything was fine.

When I picked up the car, the shop assistant told me the alternator was on it's way out.. He said the tester showed the alternator is not putting out a proper charge and will need to be replaced and that I should call the tech for more details. I haven't called him yet, so I don't know the full story. Car seems to run fine (and has for the last 4 days since I picked it up) with no battery light coming on or anything. I might bite the bullet in a month or two and swap out the alternator with a Bosch rebuilt... I guess there is no way to know if the brushes will fix everything until you try it!

Definately don't pay $400++ for an alternator from the dealer! PartsShop should be able to get you one for less! I believe the going price is about 1/2 what the dealer quoted you for a Bosch rebuilt (could be wrong).

Let me know how you make out! Good luck!

Neal