89 300E - Bad Alternator or Bad Regulator?

How do you determine if it's the alternator or the regulator that needs to be replaced? I can not afford to spend $100+ for a new alternator, only to
find out that it was the regulator that was actually bad. (I have a good quality multimeter that I can make measurements with)
At low and high engine speeds, the DC voltage remains at 12.4 V. The battery is nearly new, and I'm confident that it is good.
Thanks,
Bob Boles Murrysville, PA snipped-for-privacy@hotmail.com
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why dont you get a new regulator for little bucks...then see?

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Correct me if I'm wrong, but in my limited experience, when the engine is revved at high speeds, the voltmeter should be in the 14+ Volts category, not 12.4V!!! That way there is a re-charge on the battery. At least that is what I've witnessed my ex-E 190 doing...
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*cabob1984 wrote:

to
Really, if you own a '89 MB and cant spend a poor $100 then you probably didnt choos the right car...
Nuf said...
For the alternator, do you know any electronics? If you do and know how to use that mulitmeter of yours then you should measure the diodes on that regulator and check that they are ok. If they are, try to rev the engine @ > 1500, then the output should be above 13.5V. If the output varies a lot then the regulator is probably broke...
Hey, change the regulator, if that doesnt fix it, do the alternator.
$100, whats that...
-
Thomas
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If you have the time, take out the alternator and do a couple of checks. First of all, inspect the brushes. These are often worn down to nubs on older cars. Next, using your DVM, check the diodes. There will be a set for the field winding, and one for the armateur (sp?). Also check the continuity of the windings and the condition of the commutator.
These things are really pretty simple, and problems tend to be obvious. If the alternator looks OK, replave the regulator.
Steve

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Problem Solved ! :) Turns out that the brushes on the the regulator are a normal wear item. I found a non Bosch version of the regulator at a local automotive electrical store for $20.50. It took about 30 seconds to remove the old one from the back of the alternator. There are simply 2 phillips screws holding it on. Then, about 30 seconds to install the new one. Here are the diagnostic readings I had:
Battery terminal voltage with engine not running: 13.01 Volts. Battery terminal voltage with engine running BEFORE replacing regulator: 12.4 Volts Battery terminal voltage with engine running AFTER replacing regulator: 14.4 Volts
The brushes on the new regulator appeared MUCH LONGER than the brushes on the old... apparently defective regulator.
My advice: If you suspect an alternator problem... remove the regulator and replace it. That's most likely the problem!!!!
Bob Boles Murrysville, PA snipped-for-privacy@hotmail.com ===============================================================================

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great!

and
dude that was the first advice we gave YOU!

dooh...of course they were longer...your old ones have worn...we are talking frinction here...moving parts...touching

ooh and...I am pretty sure..in a couple of months, you will need to find a Bosch version...cause not only the regulator side wears..but also the alternator side...and from what I have experienced...the older the alternator...the more it needs original Bosch regulators...

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I am having the exact same problem with my '92 190E 2.6. My question is what is the fastest way to remove the alternator for service? There is very little room to work, did you remove it from the top or under the car? and how long did the job take? any special tricks?....thanks...Rick ( both cars are similar engine layout )
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Did have to remove the alternator to replace the regulator. There are two Phillips screws that attach the regulator to the back of the alternator. It's very easy and accessible.

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Thats what I meant, what were the steps to remove the alternator ?
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I'm sorry the (very important word) NOT was dropped somehow. I did NOT have to remove the alternator to change the regulator. I don't know the steps for removing the alernator, but I'm sure there are a bunch here that do.

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