300SDL no start! Alternator, brushes, voltage regulator?
 

Hello,

I've recently had a problem with my 300SDL and I really would like to get some advise ASAP if I may because I'd like to first get some input before I listen to all these local know-it-all shops ($$$$).

I recently was having problems starting my car (battery dead). It was an MBZ battery from year 99 so I did not think it should be dead. But nevertheless the headlights were dim and the power windows were working slowly, so the battery was replaced with brand new.

Not even two weeks later, I came home and noticed the lights looked very dim on the garage door in front of me. When I went to roll up the windows, they were going slowly. I thought, oh no, not again. Sho nuff, when I turned it off and tried to start it, cranked once VERY slowly then nothing -- DEAD again.

Now I think that the alternator is bad but I am very ignorant as to the electrical system and am hoping someone will shed some light on this issue for me.

IF I am having trouble, is it necessarily the alternator? I searched and searched trying to find some light at the end of the tunnel and it seemed that some were saying that perhaps it was only the brushes or voltage regulator that was bad, and in fact the alternator would still be in working condition? Is this correct?

I would have NO way of changing the brushes by themselves since I do not have a soldering iron or anything like that but what about the voltage regulator? Does this include brushes? Would this be possible for someone with limited knowledge to do?

I am pretty desperate to find out what is wrong since my car is effectively inoperable (I can start it with the charger pack and maybe even by itself after it has sat for a while -- but if I start it and then turn it off and start it again, it is surely dead). Thanks for any opinions or input you can offer. All the mechanics around here (SF Bay area), at least locally, are anxious to change the alternator and charge retail price plus tons of labor, etc., etc. and I would really like to first make sure that the alternator really DOES (or does not) need changing before I would proceed.


Thanks
Larry Ferguson
1986 300SDL 163K mi

My local alternator/starter/any electrical motor you can find repair shop will test my alternator for free. The local battery shop will check my battery for free. So perhaps you can find some place in your area to help get your on track.

As for trouble shooting the regulator and alternator, I am sure it isn't too difficult to do but I would have to read the manual carefully. You would need a multimeter to see whats going.

In the meantime, if you can get a battery charger plug it in but don't cook your battery. Hopefully it should be enough to give you a start. Keep all accesories OFF while driving, you won't be able to use headlights, so use some common sense there :rolleyes: .

Good luck and let us know what turns up.

As TXBill has indicated this is a very simple procedure:

1. Get the car running (jump it if you have to)
2. Get a digital tester (borrow or buy one for $10-$15)
3. If it reads in the 12's with the car running, you have an alternator or voltage regulator problem
4. Start with the VR as it is incredibly easy. Two screws in the back of the Alt and it pops out. Once out it'll probably be worn brushes. I paid around $35 for a VR which includes the new brushes already attached.
5. When you pop the VR out, shine a flashlight into the back of the Alt and check out the diodes (the copper tracks that the brushes line up with). One of mine was trashed and it ate another set of brushes before I caught it.
6. If brushes and diodes look good, you'll probably want to get the alt rebuilt. This was a bit more difficult removing and re-installing but it still is do-able.

Don

Thanks everyone for your input.

I guess this really does show my ignorance but I went outside today to tackle the 10 minute job, and 2 or 3 hours later have accomplished absolutely nothing but getting more FRUSTERATED.

All over the alternator I looked, but the only two screws I found (and took out) were off part number 012 545 24 28 which had wires going into it (and obviously of different size as well) that was on the TOP of the alternator. But I could not find one other screw on the whole outside!

Is it required I open the alternator or gain entrance to inside to replace the voltage regulator? I have the part now but did not see ANYTHING resembling it on the outside of the alternator -- top or bottom, front or back.

If anyone could PLEASE give me as much description as possible where to look, I'd really appreciate it. I really NEED to get this done and am hoping it will do the trick.


Larry Ferguson
86 300SDL 163K

Larry:

I believe the voltage regulator is just above the plug where the wires are. I can't check right now on my 300D, but you will need to pull the tray underneath to reach the alternator, probably. It is on the passenger side down low, not accessable on the W124 from above.

Peter

Here is a horrible picture I know, but camera and lighting quality are both not great so that's the best I could do. This is my alternator and on the back, there is that black plug thing with a wire but NOTHING else removeable and NO visible screws. Am I missing something? This IS the right piece, correct? Thank you.

http://home.attbi.com/~larferg/alt_0001.jpghttp://home.attbi.com/~larferg/alt_0001.jpg

Someone was nice enough to private message me telling that this in fact was the AC compressor and not the alternator! When I went out there and actually was working on the right part, it took around 10 MINUTES!!!!!! And I wasted hours looking around like a moron with 0 progress and was wondering why! Now the true test comes and I will see if replacing this voltage regulator cures my problem, or if I will indeed need to change the alternator. Thanks again all for the help.

Don't be too hard on yourself!! At least you know what the compressor looks like now! ;) Oh and the alternator!!:D and the regulator!

Man, you wewnt to fix one thing and now you know all about 3, what a bargin!:D

You have to crawl before you can walk! :) I still can't find the manual shut off for my engine... it's pictured in the owner's manual, can't find anything that even resembles it on the car itself. There's always something we're clueless with!