W123 alternator / voltage regulator question - PeachParts Mercedes-Benz Forum

AJD · #1 03-17-2010, 08:42 PM

The 240D is having starting issues and at first glance, the brushes in the voltage regulator appear to be short. But never having pulled them before, "short" is a relative term to me.

From the pictures, I assume these are a first place to start? Do these look like they need replacing?

I should mention the symptoms: battery is draining (obviously not being charged). My daughter was the last one driving it and she said the battery light came on, on the way home. The next day, dead battery.

I thought it may be the alternator, but figured I would pull the voltage regulator first, based on searching the archives.

Also, I have a W123, 300D ('83 or '85, I forget) parts car. It has the double pulley style alternator. Anyone know if this would fit the '81 240D (just forego the outside pulley)?

And is there a way to "bench test" the voltage regulator with a multi-meter?

Thanks,
Andy

TnBob · #2 03-17-2010, 09:13 PM

Those dont look the best but should at least keep the battery charged.

You might consider pulling the alternator and taking it in to Autozone or the like. I always stand by the tester to see what the readings are too.

vstech · #3 03-17-2010, 09:44 PM

yes, those look pretty short.
yes the alternator from the 300D will fit right in there, but you will need to swap pulleys over. the 240 belt is too big for either slot in the 300 pulley.
why don't you pull the regulator from the 300 alt, and compare lengths of brushes... and swap just that if it's good...

AJD · #4 03-17-2010, 09:47 PM

Yah, I was going to try just swapping regulators first.
But is there a way to test just the regulators...?

Thanks.

vstech · #5 03-17-2010, 09:49 PM

other than visually, or measuring them with a ruler...
put them in a alternator, and have it tested at a garage. only thing I can think of.
I'm sure there is a meeter setting you can measure the diodes or something, but I've got no clue how that would be done.

AJD · #6 03-20-2010, 05:26 PM

Well I went to pull the voltage regulator and/or alternator on the parts car today, and being that it's a 300D with turbo, it's not NEARLY as easy to get to as the 240D. So for what it's worth, I put the charged battery back in the 240D and took voltage readings with the car running across the temporarily removed positive voltage cable and negative cable (to isolate the battery). I was getting ~14 volts, so the alternator was still working even with the old brushes and regulator.

My hunch is that the brushes in the voltage regualtor were starting to intermittently not work, so for $8.48 at the hardware store, I bought new brushes and resoldered them in place. After installation, I checked voltage readings again, as before isolating the battery, and was getting closer to 15 volts on the DMM.

(Pictures of the new brushes in the old voltage regulator attached.)

Thanks everybody for all the pointers, and as always the very helpful archival posts!

leathermang · #7 03-20-2010, 05:35 PM

Since you have just done this..
perhaps you have the make and model of the brushes you bought...as a reference in this thread ?

AJD · #8 03-20-2010, 07:10 PM

I didn't think to measure the size of them, but do know that what the hardware store had was all in inch measurements. Of course they were in those plastic pull out trays, so I would have needed to physically measure the actual ones I purchased to verify exact size, since most of them are all mixed up. I just took my old ones in and matched them side by side.

In any case, there wan't any 'brand' on them. They were simply in the variety trays at one of our mom & pop hardware stores in the section with all the other carbon type brushes for vacuum cleaners, electric motors, etc. And the old ones are now history.