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  #1  
Old 08-29-2011, 06:55 PM
1975 Mercedes 300D w115
 
Join Date: Aug 2011
Location: California
Posts: 24
w115 300D Alternator Question-HELP!

Ok, I bought the 1975 w115 300D knowing it had some issues, the battery keeps draining, driving around town, its a new battery and will hold a charge.

So I imagine that the alternator is bad and not charging the battery, thus the drain.

Can someone show me a picture of the alternator and how to take it out and to test it.

Thanks

Keith
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  #2  
Old 08-29-2011, 08:31 PM
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Quote:
Originally Posted by merc4him View Post
Ok, I bought the 1975 w115 300D knowing it had some issues, the battery keeps draining, driving around town, its a new battery and will hold a charge.

So I imagine that the alternator is bad and not charging the battery, thus the drain.

Can someone show me a picture of the alternator and how to take it out and to test it.

Thanks

Keith
You can google "testing an alternator" and get a good idea how to do it, it is very simple.

There have got to be pics on the net showing the 300D alternator plus R&R. Look around a little bit.
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  #3  
Old 08-29-2011, 09:03 PM
1975 Mercedes 300D w115
 
Join Date: Aug 2011
Location: California
Posts: 24
Quote:
Originally Posted by strelnik View Post
You can google "testing an alternator" and get a good idea how to do it, it is very simple.

There have got to be pics on the net showing the 300D alternator plus R&R. Look around a little bit.
Sucks, I have to crawl under the car to get access to it. Now the brand new battery may be shot too.
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  #4  
Old 09-09-2011, 04:16 PM
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Make sure the glow plugs are not still on while the car is running.
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  #5  
Old 09-10-2011, 03:52 AM
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Location: So Cal, High desert
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Where's the drain ??????????

Quote:
Originally Posted by merc4him View Post
Sucks, I have to crawl under the car to get access to it. Now the brand new battery may be shot too.

If you know you have a drain, remove one of the battery terminals when you park the car.

The battery doesn't die from being discharged, charge it up again soon.
The longer it sits without 'juice' is what kills it !! especially fully discharged.

My first guess was also the glow plug system , not the alternator, being the drain culprit.

You can check with the weak battery, get the car started maybe jumped with doubled up cables.
Best in the dark, let it idle, when you rev up the 'gas' lightly the interior light should be getting brighter, when you let go of the gas it should dim again (given the idle is low enough.). The same with the headlights, but those are harder to see from inside the car.

That would tell you , if it's charging.
The drain could be caused by just about anything electrical on the car.

Shot back a QUICK REPLY, when you can

good Luck

Alex
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  #6  
Old 09-10-2011, 10:59 AM
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I've got an alternator for your car--e-mail me for photos


Tim Kraakevik
kraakevik@voyager.net
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  #7  
Old 09-10-2011, 04:56 PM
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Most alternators dont fail, but the internal regulator wears out. You can remove this regulator from the back of the alternator and compare the brush length from yours to a new one. Also its very important that the belt is at proper tension.
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Old 09-10-2011, 04:59 PM
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If it runs you can take it to any good parts house, AutoZone, NAPA and they will test it on the spot and can usually tell you what the problem is.
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Old 09-12-2011, 11:25 PM
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Before you do all that previous stuff, get into the car and turn the on but do not start it. Make sure the generator light is on, or alt light. If it's not on, you need a new bulb. If it's on, take it in for testing.

If the alt light flickers when you drive, you may need new brushes.
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  #10  
Old 09-13-2011, 12:05 AM
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The brushes are part of the regulator. An auto parts store generally cannt separate a faulty regulator from a faulty alternator during the test. Regulators are rather inexpensive in relation to a replacement alternator. And truth be told, most rebuilts are just a new regulator and maybe a set of bearings.
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Old 09-13-2011, 02:28 AM
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AWOL

Looks like our original poster has gone AWOL.

I can sell you an alternator, that you may not need, too.

The last couple of posts combined will give you a good picture.

The (red) light on your gauges should come on (solid and bright) when the ignition is on with out the car running. Once the car is running and the idle is raised enough that light should turn off ( compare my earlier post, with the interior light, when the idle or engine speed is high enough the regulator will let the alternator charge, meaning, that the red dash light goes out and the interior light brightens because of the charge).
If this red light only dims , the brushes are worn and need replacing. See other post, replace regulator screwed into the back of the alternator.

As I said before , the drain is possibly elsewhere...

Alex

BTW, I'm in L A (N county), where are you ?
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  #12  
Old 09-13-2011, 03:09 AM
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In Stockton 60 miles south of Sacramento. I've got a daughter in San Dimas.
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