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Alternator dying?

Posted: Tue 22 Jun, 2010 10:55 pm
by bruceT
My 93 W124 300D has been going strong on veg oil fuel, but on Sunday evening while driving home after a day out with the Goat Island Skiff* I've recently finished building, the charge light on the dash started flickering. By the time we got home the battery was drained due to all the lights, including the trailer being on during the drive home.

I charged the battery overnight, and drove to work the next day, but after about 10km, the charge light started flickering again. Is my alternator kaput? I've recently replaced the serpentine belt.

* The reason for my recent absence!

Re: Alternator dying?

Posted: Wed 23 Jun, 2010 7:05 pm
by John Green
By the look of that boat you are a cleaver man, so should be able to do an alternator reco yourself. Strip it down, check the diodes are OK, clean it up and fot a new regulator/brusg pack. easy.

Re: Alternator dying?

Posted: Wed 23 Jun, 2010 7:49 pm
by bruceT
Hi John

I trust you're well? I might just try and give it a go then. The funny thing I've noticed is that the the idiot light only comes on when it the engine has warmed up and if the RPM drops below 1000.

How much time is involved to do it and is there a website somewhere that explains the process?

Re: Alternator dying?

Posted: Wed 23 Jun, 2010 9:08 pm
by Tony From West Oz
That added information makes me think of a blown diode in the alternator. This reduces the output current from the alternator and it causes this symptom.
If it were the brushes, I feel it would be happening at any RPM, not just at idle.


Re: Alternator dying?

Posted: Thu 24 Jun, 2010 11:25 am
by bruceT
Thanks Tony, yes I think you are correct there.

I really do not have the time to do this myself, so realistically, is my mechanic going to suggest a new alternator anyway? Maybe John can answer whether a diode would be any cheaper than a new or reconditioned alternator once labour is factored in?

Re: Alternator dying?

Posted: Thu 24 Jun, 2010 3:10 pm
by AMG
To be brutally Honest Bruce, the BEST solution is to rebuild your own alternator.

that way you know it is still genuine.

a reco alternator may be cheap non-genuine. you can get the new slip ring commutator bearing and brush / reg-rec assembly from any bosch service centre.

I was going to do this, until I found that I could buy new german made bosch high output (150A) alternator for about 50% more than a reco unit.

Re: Alternator dying?

Posted: Thu 24 Jun, 2010 6:55 pm
by bruceT
Hi Joe,

Wow, 150A. I guess these are required to power the modern car. I think my old W123 300D had a 50A! Not sure what this one is.

I guess I could have a go at it. It's just that I read somewhere that these kits can be quite expensive, so my concern was that I might not be saving any money. But I really should be looking at DIY because I can learn from it. It's just that when it comes to electrics I barely know my +'ve from -'ve. and as long as my lack of electrical nouse is not going to bite me in the bum if I do pull it apart, then I guess I'm up for it.

Re: Alternator dying?

Posted: Wed 01 Sep, 2010 10:40 pm
by MB300D81
Comming back from work on the M5 and all of a sudden the ABS light came on then the CD player started to flicker then light started to dim.
I stopped on the side of the road and silly me I turned the engine off and could not start it.

I managed to get it started with a jump start from my wife's car and got the car home . Thank God it is not a petrol engine.
Then took the voltage regulator out. Seems like it is completely worn out.

Other than replaceing it is there any more advises?


Re: Alternator dying?

Posted: Thu 02 Sep, 2010 7:00 am
by benzfan
I'd replace it - it's something like a $35 part if I recall correctly.

Re: Alternator dying?

Posted: Sat 04 Sep, 2010 9:16 pm
by MB300D81
I just replaced the voltage regulator and things are back to normal.

I would have loved to order it from MBspares but I could not wait until Monday to get it as I needed the car over the week end.
I must admit MBspares offered lower price as they usually do.

Re: Alternator dying?

Posted: Wed 03 Nov, 2010 7:20 am
by MB300D81
Fine people

Our new w124 needs alternator regulator. but the regulator on this car is different to the one in the other car.

In fact the whole alternator looks didferent.

Question is did the w124s come with different alternators?

Here is a photo of this regulator ...

Re: Alternator dying?

Posted: Tue 09 Nov, 2010 9:12 pm
by MB300D81
MB300D81 wrote: Question is did the w124s come with different alternators?.
I just found out that some cars are fitted with Bosch alternator and some others come with Valeo alternator.

Two different alternators and totally different regulator shap and orientation.

just sharing the info..

Re: Alternator dying?

Posted: Sat 07 Oct, 2017 12:23 am
by 260e3

i just had my second breakdown in about 95,000kms - same symptoms as above, bluetooth stopped on the stereo, then abs light - then the car died.

w124 260e.

the road assist guy jumpstarted the car and it was idling ok with 9.5volts on the battery.

it was the brushes. luckily the local guy rigged up a replacement set of brushes onto the reg and i was away.

real question is if the car was running on the battery and it was below 12v - why wasn't the charge light on?? what does it take to get it to come on???

btw the charge light is on with the other dash lights when you first go to start it ( check light )


i think i need to install a volt meter now if the light isn't going to tell me when the car will die.

Re: Alternator dying?

Posted: Fri 27 Oct, 2017 10:28 pm
by crazycrowbar
Exactly the same happened to me a couple of months ago, exactly as you describe it......
Easy and cheap fix.....Regy=ulator was worn out.....
I have the same question now........Why did the alternator/charge light did not warn me?

Re: Alternator dying?

Posted: Thu 04 Jan, 2018 8:44 pm
by 260e3
i guess it is a mystery about the charge light..
but why have one..

i will install a volt meter to be sure..

Re: Alternator dying?

Posted: Thu 11 Jan, 2018 4:11 pm
All this talk of regulators recently got me to pull mine out for a look.

Lucky thing I did as it looks as worn as the one in your picture that failed!

Still waiting for my replacements to arrive from overseas. Should of bought locally :banghead:


Re: Alternator dying?

Posted: Thu 11 Jan, 2018 5:33 pm
by Christo C
These regulators are quite repairable
The dude talks about two types, the W124 one is the first one he shows, and the second one he tells how to replace the brushes.

Re: Alternator dying?

Posted: Fri 12 Jan, 2018 10:27 am
I've purchased the brushes now and will solder them in when they arrive. Been on holidays off work for a month and haven't been able to drive my w124 the whole time. Irritating to say the least.

eBay seller still has not even sent the regulators I ordered weeks ago, as soon as the expected delivery time expires I will as always start an item not received claim. Don't know why these clowns list items for sale they don't even have or have no intention of even sending.