alternator help! - PeachParts Mercedes-Benz Forum

bigfredb · #1 11-08-2009, 11:33 PM

The alternator on my 83 300sd is dead so it needs to be r and r. Are there any tricks I need to know, special tools, tips,etc?

Jeremy5848 · #2 11-09-2009, 12:45 AM

How do you know it's the alternator? It could be the regulator, much easier and less expensive to replace.

t walgamuth · #3 11-09-2009, 06:23 AM

Quote:

Originally Posted by Jeremy5848

How do you know it's the alternator? It could be the regulator, much easier and less expensive to replace.

x2.

Replace the reg first since it is so easy.

fullcircle · #4 11-09-2009, 09:57 AM

x3.
My '83 240D battery was gradually losing charge, with no indication of any charging problem from the dash light. It failed to start the car Saturday. There has been no past problem of battery drain. Not sure of your symptoms or what leads you to think it's the alternator, but I searched the forum and found out some things:

-If you turn the ignition key to the glow cycle and your battery light does not light, that could very well be your problem. That light needs to work for the charging system to work.

-If the voltage regulator brushes are not making contact, the dash light will not indicate a charging fault (but it will light with key in glow position).

-Dieselgiant.com has a write up with pictorials. He did it from under the car, I could do it from the top on my 240. He indicates philips screws mounting the VR, mine were Torx head.

When I pulled my VR one of the brushes fell out into the alternator (easily retrievable), but that explained my no-charge problem and the lack of the dash light to indicate the problem.

bigfredb · #5 11-09-2009, 10:24 AM

I will take a look at the Diesel Giant DIY.

Thought it was the alternator as the charge going to the battery was measured at 6.4vdc (which obviously isn't good).

I replaced the battery last week.

I do occasionally get a light on the dash but it comes and goes (bright to dim, flickers, etc.). Would this still indicate a VR issue?

toomany MBZ · #6 11-09-2009, 10:55 AM

^ Yes, a two screw 5 minute job. At worst, you'll have a spare VR.

bigfredb · #7 11-09-2009, 12:04 PM

AAARGH!!

So far none of the auto parts stores in my area have the Voltage Regulators. And of course they all want big $$$ to 'special order' them.

Even the stealership didn't have one in stock.

toomany MBZ · #8 11-09-2009, 12:35 PM

Ouch. I've bought one at the local autozoo, but it's been a while. Try Phil.

bigfredb · #9 11-09-2009, 01:04 PM

Pulled the Voltage regulator. The two 'posts' are each about 1/2" long, so they probably need to be replaced.

One of the two has a smaller secondary groove in it (right in the middle). Is this normal wear?

bigfredb · #10 11-09-2009, 04:46 PM

Finally tracked one down at a NAPA about 25 miles away. Since my car was broken, had a friend pick it up.

It looks kind of like the one that came out of the car, but not exactly.

How can I check to see if the car is getting a charge without going to the Auto parts store?

fullcircle · #11 11-09-2009, 05:58 PM

I'm not sure what you mean "so you don't have to go to the auto parts store..." You'd mentioned your friend had picked up the VR. Maybe you're talking about installing the new VR and then getting the charging system checked at the Auto Parts store? Anyway, search the forum, titles only, key word "charging." You'll get a lot of information. I would install a new VR then, with the car running, check voltage across the battery. I think you're looking for around 14 volts.

bigfredb · #12 11-09-2009, 06:10 PM

Yes, that is what I was talking about. Charging. It took quite a few different searches to find the info I wanted.

I started another thread to ask questions about the Voltage regulator itself.

SD Blue · #13 11-09-2009, 07:39 PM

With such low voltage, I'd be suspicious of other problems with the alternator.
Before changing the regulator, with the meter in VAC, check across the battery while running. If it is more that a few millivolts AC, you may have damaged rectifier diodes in the alternator. If so, changing out the voltage regulator may be an expensive "test" as the AC voltage may damage the new regulator.

An alternator initially produces AC voltage, then rectifies it to DC voltage. The regulator smooths it out a little more then helps to control charging of the battery. If the rectifying portion goes out, it will soon destroy a new battery and the regulator.

bigfredb · #14 11-11-2009, 01:40 PM

SD,

I will give that a check.

In any case, I have a Voltage regulator on the way from an online supplier. (Mainly because NOBODY in my area had one, not even the stealership)

Several places around have alternators, so that will be a backup.

fullcircle · #15 11-11-2009, 06:56 PM

I just received my voltage regulator today for my '83 240 and the posts on the new one were not too much more than half an inch. Maybe 3/4," but I don't think they were even that long. In the event that you do need an alternator, have you considered a local re-build shop? We (my dad and I) have used a guy who has done a really good job for us, albeit no Mercedes parts have ever gone to him. He looks at the piece and quotes a repair after he knows what's wrong with it. Has stood behind his work, too...fixing a starter a second time, even though it was a year later. I'm only throwing this out as a suggestion. The cost is usually substantially less than a replacement. The only drawback is turn-around time. I had to just buy an alternator for my wife's car because I couldn't wait the day or day and a half to get the car running.

Good luck. Hope your VR fixes it.