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  #1  
Old 01-06-2019, 06:52 PM
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Normal output for W115 alternator

I suspect mine is toast. Bearing noise too. Just wondering what voltage to expect with accessories off at idle measured from the battery.
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Old 01-06-2019, 06:59 PM
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In a perfect world, 13.8 to 14.2 V assuming a fully charged battery and no electrical load. If it takes a high idle to get up to the range that is ok. Any load/drain from an accessory or a shorting battery will lower the voltage. Realistically, 13.4 to 14.4V is fine
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Old 01-06-2019, 07:11 PM
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Thatís what I thought coming from the gas world but didnít know if it translated to diesel. I loaned out my multimeter and am using a backup that doesnít show decimal points and it fluctuates between 12 and 13 volts. Harder to start after a run involving the headlights etc. so I figured itís time to rebuild it.
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Old 01-06-2019, 09:21 PM
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Dumb question but what alternator should have come with this car? I canít tell but it looks original. And I want to order the bearings and voltage regular to attempt a rebuild.
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  #5  
Old 01-07-2019, 09:49 AM
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Quote:
Originally Posted by BluePanzer1975 View Post
Dumb question but what alternator should have come with this car? I canít tell but it looks original. And I want to order the bearings and voltage regular to attempt a rebuild.
The most reliable way is to ask your local friendly Mercedes dealership if they'll look up which part you need via your VIN information - they'll be able to give you a part number (and probably a small heart attack for the price). Alternatively get EPC access yourself.


If you don't / won't / shan't then have a look on sites such as the site sponsors to see which part number they recommend.
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  #6  
Old 01-07-2019, 10:14 AM
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There is a fair chance the alternator has been replaced once in the life of the car. What year and model is it? Internal or external regulator? Fortunately I have a great local rebuilder to take items to and get the original correct unit back with a thorough rebuild at a great price. Perhaps there is one in your area to source parts.

Good luck!!!
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  #7  
Old 01-07-2019, 12:22 PM
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Post W115 Alternator

I was thinking the 115' still had the external regulator , your signaoure says 1975 so here's the most likely one :

MERCEDES-BENZ 230 1974-1978
MERCEDES-BENZ 240D 1974-1983
MERCEDES-BENZ 280 1973-1976
MERCEDES-BENZ 280C 1973-1976
MERCEDES-BENZ 280CE 1978-1981
MERCEDES-BENZ 280E 1977-1981
MERCEDES-BENZ 280S 1975-1976
MERCEDES-BENZ 280SE 1977-1980
MERCEDES-BENZ 300CD 1978-1985
MERCEDES-BENZ 300D 1975-1985
MERCEDES-BENZ 300SD 1978-1985
MERCEDES-BENZ 300TD 1979-1985
MERCEDES-BENZ 450SE 1973-1976
MERCEDES-BENZ 450SEL 1973-1980
MERCEDES-BENZ 450SL 1974-1980
MERCEDES-BENZ 450SLC 1974-1980

This is the 55 ampere one with internal regulator, if the bearings are bad it trash, order in the 65 ampere one for a 1985 300D, it'll bolt right up and have more out put .

Be aware that the brand of the regulator has everything to do with the charging voltage.

I only use BOSCH branded regulators for this reason .
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