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  #1  
Old 02-16-2006, 01:07 AM
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85 300SD cold starting/electric problems

So, here's the deal: Today we had some snow and cold car ran fine but as the evening progressed the radio went out, then sometime later the antilock light comes on so I am thinking that if I try to restart the car it will go away (I decide to do this at an intersection, snow is everywhere, doh!!!). Car doesn't start, starter won't turn over, when ignition is engaged the lights dim, speedo/tach needles jump. Now this has happened in the cold before, car sat overnight in the cold and won't start, engine would barely turn over. Regular jumping doesn't help (battery to battery), only way to get it going is to use a heavy duty battery jumper. Figured it was the batter, got a brand new MB battery. So today, after pushing the car into a parking lot and waiting for AAA to come and jump the car, I've noticed driving back home that the lights were very dim, speed and tach needles were way below normal reading, but when the car just has the key in the ignition (just battery power) all lights are alright. I've read these threads: '86 300 SDL - Mystery - Please Help
http://mbca.cartama.net/showthread.php?t=10787

and from reading them it would seem that the alternator gets stuck. All other possibilities seemed to be ruled out: new battery, glow plugs work, starter works, fuel is getting to the engine. I will try to check this out tommorow making sure all accesories spin and that the cables to the starter are more or less alright. Am I missing anything? Any suggestions?

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Old 02-16-2006, 11:12 PM
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It could be some sort of short that is only active once the key switch is turned on. Also as you suspect the regulator part of the alternator may be bad. Finally all main cables and ground cables need to be good and have good connections !!
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Old 02-16-2006, 11:21 PM
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The alternator is intermittent. Sometimes it charges the battery........sometimes it doesn't. Likely caused by the brushes worn down to almost nothing. Change the regulator and see if the problem goes away. It's a common problem.
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Old 02-16-2006, 11:25 PM
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If your alternator stuck, your belt will burn up and finally break.

From your first story, it sounds like the alternator is not charging the battery.

Make sure your battery is charged and then try this with a voltmeter:

Start car and let it idle for a few minutes

Turn on the headlights and read the battery voltage, it should be above 13.2 volts. If you bring the idle speed up, the voltage should increase to 13.8 - 14.0 volts. If not, then the alternator is not charging the battery.
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'85 300SD - 317,000 miles (sold)
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Old 02-17-2006, 02:37 AM
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Thanks for all the responses, tommorow I will be getting a battery charger to get this beast going again, and will check the voltage at the batt while reving, will also check if the alternator spins at the time. If I sense a problem then I will try a new regulator if the alt isn't charging, but if it doesn't spin should I go ahead and get a new alternator or is there some bearing (or some such cheaper to fix problem) at fault?
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Old 02-17-2006, 09:41 AM
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I'm with Brian, it's the brushes. The ABS is the first light to come on with low voltage, been-there done that on my '91 4matic. Alternators were not a strong point on Mercedes, always too small.

You might be able to remove the regulator, stretch the braided wire to the brushes so that they'll contact for a few days until your new regulator arrives.

Cheap jumpers won't start your car, but if you wait for them to charge the battery for a while, it will start, some people call these "booster cables". I carrry a good pair made from 3/0 welding cables and 400amp ends, will start a car with no battery in it.

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Old 02-17-2006, 12:36 PM
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You said that it was snowing. Do you have the heater on full blast? I have found that my car (an 85 300sd) will not charge when the heater blower motor is running full blast. Of course I suspect my battery and alternater need to be replaced, but that blower motor draws quite a bit of current when opperating at full blast.
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Old 02-17-2006, 09:52 PM
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Some of these alternators do not provide a lot output at low rpm. With lights on and the blower motor on high and the defrost on, it will barely keep the battery at 13.2 volts. Increase the rpm by 500 and your at 13.8 - 14V. Mine does thins and I've got a brand new regulator.
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'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

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Old 02-17-2006, 11:38 PM
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Well as soon as I got the jump from the tow truck I rev'd the engine a little to get it to charger the battery, that didn't seem to help. As for running the heat, I only turned it on after we got going and nothing seemed to change.

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