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  #1  
Old 07-15-2022, 02:56 PM
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How to test alternator out of car?

Alternator in my 1981 240D is electrically OK, but has seriously ovalized mounting holes, so it sits very crooked. I have another alternator that looks good, and has bushings so no ovalized holes. Can't remember where i got it. Is there a way to test it out of the car with a multimeter before installing it to find out if it works? I am thinking it was pulled for a reason, but maybe the V.regulator was bad, which i could just switch from the known working one.

Also, how does one switch the pulley and the little finned fan under the pulley without mangling either?

Thanks in advance, you fellow Mercedes victims have always pulled thru for me!

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Old 07-15-2022, 05:23 PM
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Take it for a run up test at an alternator repair shop. Impact gun for pulley removal.
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  #3  
Old 07-15-2022, 05:59 PM
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Most major auto parts stores (Auto Zone, etc.) will test the alternator for free.
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Old 07-15-2022, 06:33 PM
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You've posted about this before haven't you?

Did you try shimming the alternator?
If it wasn't for the easy warranty, I would have continued to run it.


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Old 07-16-2022, 12:57 PM
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Do those shims stay put?

I did post about this a few months ago, but never thought of just wedging shims like in the picture! I kept using it, but ran out of adjustment, so the belt was very loose, and also wearing excessively on one side. The other alternator i was asking about turns out to be slightly different, smaller holes and probably won't fit. Maybe from a VW or something.

Are the shims in the picture just a stack of washers? Tell me more!

Last edited by sun tortise; 07-24-2022 at 10:15 PM.
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Old 07-16-2022, 01:46 PM
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Just a stack of aluminum crush washers and they certainly stayed put…
I ran it like that for over a month, with over a thousand miles driven.
Like I said, the only reason I swapped it is because the alternator was covered under warranty for the ovaling of the holes
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  #7  
Old 07-24-2022, 10:14 PM
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New alternator - belt way too loose!

I bit the bullet and ordered a new alternator from E-bay. It has a bit of slop in the lower mounting hole, tho not nearly as pronounced as my old one. The old belt, a "Contitech" 13 x 1030, will not tighten sufficiently within the range of the adjuster. I am wondering if the old belt, which definitely shows some wear from having been run crooked so long with the ovalized alternator, as well as some minor cracking on the inside, could have stretched that much, or if i need to order a shorter belt. Pelican shows that size, as well as a 10 x 970 (?)as fitting my 1981 240D.
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Old 07-30-2022, 01:52 PM
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Thank you

Thanks, Shern, for the suggestion about shimming. My new alternator, a crappy Flea Bay unit from Heartland Starter, has play in the pivot hole (pulley side). So is shimmed it with some old TV antenna elements flattened and folded over 3 thicknesses. New belt tightened up nicely, and am hoping for the best. I have a lot of old TV antenna elements, lol.
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Old 07-30-2022, 06:53 PM
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Happy to hear it worked!
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  #10  
Old 08-02-2022, 08:25 PM
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Post Alternators & V-Belts

1030MM is way too long .

I'd scrap that alternator, there's gotta be some place else that sells properly rebuilt alternators .

Where are you located ? .

I had several 65 ampere W123 alternators no one else wanted so I tossed them all out .

FWIW, the 1985 W123's used this *slightly* higher bolt and plug in to play alternator .

BOSCH and other quality rebuilders will automatically drill out the ovalled holes and press in a still bushing to affect a permanent repair, at no additional co$t .

Before replacing the brushes / voltage regulator, LOOK INSIDE as many will have badly worn commutator slip rings from careless previous replacement by a D.P.O. or D.P.M. .

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I did then what I knew how to do ~ now that I know better I do better
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