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  #1  
Old 11-12-2019, 11:23 AM
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w123 240d W on back of alternator

I have 2 alternators and both tested bad but I'm wondering if the brushes were just bad or it's that alternator.

Do you think these wore brushes would show a failure when bench tested?

Also, the chinese alternator from Advance has different wiring in the back.
On the older bosch, there's a + sign next to the terminal that I hook to car but on the advance alternator, it's a W sign. The + sign on the advance alternator has another electronic part plug into it. Is it possible the that the electronic part on the advance alternator is plugged into the wrong terminal?

Any advice would be greatly appreciated.

Thanks,

pete

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w123 240d W on back of alternator-20191110_163739_resized.jpg   w123 240d W on back of alternator-20191110_163749_resized.jpg   w123 240d W on back of alternator-20191110_163756_resized.jpg   w123 240d W on back of alternator-20191110_163805_resized.jpg  
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  #2  
Old 11-12-2019, 11:43 AM
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They look fairly worn. If the wires don't match the plug I'd return it.
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Old 11-12-2019, 11:59 AM
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The brush length looks short on the picture of the regulator. . May be just the picture but they should protrude more I think on that regulator.


Poor or no contact and that alternator is not going to function. I would examine the slip rings in the alternator the brushes ride on. If they do not appear too worn I might test that alternator again using the other regulator.
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  #4  
Old 11-13-2019, 06:43 AM
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I replaced the brushes but the alternator still failed a load test at Advance Auto.
I noticed the pulleys on the original and advance alternator have different size pulleys. The original bosch pully is a little bigger.
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Old 11-13-2019, 07:06 AM
t walgamuth's Avatar
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All other things being equal the bigger pulley will run the alternator at a slower speed making less drag on the motor. You'd want that on a vehicle which is raced at high rpm as an example.
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..I also have a 427 Cobra replica with an aluminum chassis.
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Old 11-13-2019, 07:19 AM
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I wonder if the smaller pulley increases the amps. The smaller pulley isn't as wide to fit the belt. I am able to pull the pulleys and swap them. They will fit on different alternators even though the nut that secures the pulleys are different sizes on both alternators.

I'm going to head out shortly to install the cheaper Advance alternator since it passed the load test.
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  #7  
Old 11-13-2019, 10:16 AM
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I was wrestling with the top spacer on the alternator tensioner rod and was able to force it in place but the tensioner rod was not working properly so I removed the alternator.

I noticed this small spacer insert that wasn't on the original alternator. Anyone replacing an alternator should check to see if this spacer is needed.

pete
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  #8  
Old 11-13-2019, 12:15 PM
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What is the condition of the Slip Ring inside of the Alternator. You should be able to see part of it with the regulator removed.

If my memory is working I think the Manual has the 2mm of brush protrusion they should be replaced. But if you Slip Ring is worn down that also effects the usable brush length.
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  #9  
Old 11-13-2019, 02:19 PM
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The W terminal is a tachometer pickup, used on a lot of diesels. The alternator you have from advance does not look like it is correct for the 240D.

I've had a local alternator shop quote me $25 to install a W terminal on my 240D alternator, which I would prefer over the stock tach pickup.
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  #10  
Old 11-14-2019, 08:55 AM
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Correct. a "W" connection is an AC feed off one phase of the stator, used for a tachometer (or a warning light relay on certain cars, thus "W".) Your harness shouldn't have a connection for the small + terminal, this is correctly used for a smoothing capacitor as illustrated. The B+ terminals of your car should connect to the two large tabs in the 3-way connector, the third tab being the D+ termination for the warning light. You must change pulleys, or your belts will be a problem.
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  #11  
Old 11-15-2019, 07:32 AM
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Thanks all. I don't have a tach on my 240d. If I were to pull a tach from a 300d, could I power it with the W terminal? Would the tach give me any useful info even if it wasn't accurate?

pete
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  #12  
Old 11-15-2019, 09:06 AM
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The tach from a 300D requires a magnetic pickup, which produces a different kind of signal. So no. You would need to add an after-market tach, and you would need to adjust the calibration with a mechanical tachometer.
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  #13  
Old 11-15-2019, 11:03 AM
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Thanks for the info.

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