Interesting alternator charging problem
 

Well, my car turned 270,000 miles last night, and it also decided to stop charging the battery. It's an interesting problem because earlier in the day all of the instrument warning lamps were flickering slightly at idle, and the battery light was glowing ever so slightly. On my way home from car54's house, the antilock lamp came on, indicating that the battery charge had dropped below 10 volts. The headlamps were also noticibly dimmer. Periodically the antilock lamp would turn back off and the headlamps would get brighter, indicating that the alternator was once again charging. By the time I got home, the antilock lamp had come on and gone back off about 4 times (on for about 5 minutes each time). Also interesting is that none of my warning lamps come on when the ignition switch it turned to the on position (only the SRS and glowplug lamps come on).

My question is this... is this likely a failing alternator, voltage regulator, or possibly an ignition switch problem? I think I am going to test the output of the alternator later tonight, and any suggestions will be greatly appreciated. Perhaps all it needs are new brushes (I hope).

Thanks so much,
Lawson

Yep, start with new brushes. Low voltage makes it do all sorts of funky things like that.

Rick, thanks for the advice. I suppose 270,000 miles out of a set of brushes isn't bad.

I had the same problem and changed my alternator.. twice.

Still happened. Turned out to be loose connections at the battery terminals..

Who'd a thunk it?

Hmm, very curious. I will put the car up on ramps tomorrow and check the connections on the alternator, as well as the connections on the battery. I originally thought it was a bad ground somewhere in the instrument cluster when I saw all of the warning lamps flickering. As soon as the antilock lamp came on, I knew it was something more serious.

Check the belt tension while you're at it.

If you replace the alternator and you require more amperage, I believe you can use the alternator out of an S320 that is about 143 or 150 amps... I read a post that GSXR had written.

Lawson,

When my 87 300E pulled those same stunts it was the Alternator failing. For some reason Benzes tend to not light the alternator warning light if the alternator still puts out even the slightest amount of electricity albeit not enough to survive on.

A quick change of the alternator put me back in business but my battery soon failed. My shop told me that it was common for the battery to die right after being traumatized like that.

Plan on replacing both...

Good luck!

ive had this happen 3 different times, times, 1 and 3 it was the brushes, but the second time it happened was a bad glow plug relay!!!!!!!

contacts had welded closed, energizing the glow plugs all the time!!! quick and simple to check!!!! id recommend it just for piece of mind.

When my SD recently experienced similar traits, I replaced the regulator, brushes and belts. The problem still persisted. It turned out that the plug at the alternator had oxidation on it, cleaned it up and it's been working fine. It needed new brushes anyway.

Tom
'82 SD
'86 SDL

Hey, Tom, good to see you again.
This might be the season for these VR's to be failing.
The SD's failed around Christmas, and my gas wagon is not charging either.
The symptoms on the gas wagon are: no charging voltage when revving the engine, (very) intermittent jump to 13.8 VDC, then back to low battery voltage.
Does this sound like the brushes/voltage regulator?
Thanks, Bob

Well, I finally got a new alternator... well remanufactured from Advanced Auto Parts with a lifetime warranty (probably not worth squat). It set me back $200, compared to $380 for reman from the dealer, or worse yet $640 for a new one from the dealer. :eek: BTW, this is a 70 amp alternator. I really like the idea of using a 150 amp alternator from an S320! I guess I'll use one of those the next time it dies (if I decide not to use the AAP "lifetime" warranty).

I still need to install the alternator... I haven't had enough time on nice days to get the job done... work work work. :( If anyone has ever worked for a theatre, you know what i'm talking about. :rolleyes:

For the time being, I've just been putting the car on a battery charger at work. It's nice not having an ignition system drawing 30 amps all the time. Diesels rock! :cool: I'm sure my battery is hating the charging/discharging cycles. I guess we'll just have to wait and see how it holds up with the new alternator.

There are indeed many things that COULD be wrong such as bad connections, but the LIKELY problem is worn brushes. The voltage regulator mounts to the rear of the alternator with two screws. Remove the VR and look at the brushes. They are most likely worn and your problem. If so, feel of the rotor sliprings and see if the brush groove is worn very deep. If it is not real deep, like say 1/16", then click on Parts Store above and buy a Voltage Regulator for $14. That will most likely put you back on the road for another few hundred thousand miles.

If the brushes are in good shape, then remove the connector on the alternator and pull the cover from the connector. See if the wire is crimped tightly to the connector pins.

Hope this helps,

Larry,

Thanks for the advice. I will check the brushes before I remove the alternator from the car. If I can simply replace them for $14 and it fixes the problem, I will return the "new" alternator to AAP.

Well, I went ahead and replaced the alternator yesterday. All is now well with the charging system. :)

However (there's always a however on a Mercedes... or so it seems) my antilock warning light now comes on after about a mile of driving. Fix one thing, and something else breaks. :( Hopefully it's just a dirty/damaged wheel speed sensor. I will check this out soon.

Thanks to everyone for the support!