How Do you check alternator while in car?

[Mr Goodfahrt]

I did a word search.... how can you check an alternator on a 123 300D while it is in the car? Can you just remove the hot lead from the battery while it is running and use a voltmeter?

Thanks... am only showing 12.2 at cigarette lighter. Pulled all fuses 1 at a time and also swapped out voltage regulator with no change. Old brushes were down to 1/4 inch. Dash light has never come on.

[Rick Miley]

You don't have to remove anything. Just use the voltmeter on the battery terminals. Check with the engine running, and check with engine not running. Should be higher while running, and around 14 volts.

No, the dash light doesn't come on.

[Mr Goodfahrt]

Thank you... I tested as you suggested. Then to be certain, I unplugged the alternator at the plug next to the voltage regulator. Symptons did not change. I am amazed at how far you can drive without the alternator working! Drove several hours with only .2 drop in voltage (no accessories running.. used only brake lights a turn signals). These batteries must be beasts.

Located a used alt for $50 and will intall this weekend.

[lietuviai]

FYI, in the future, it's not a good idea to disconnect the alternator wiring or remove the battery while the car is running. You can burn out the diode in the alternator. In your case since you're replacing your old one it doesn't matter.

[Mr Goodfahrt]

Got the job done yesterday with used 65amp model from 300SD acquired from Potomac German Auto for $50. Couldn't figure out how to free up the tension adjuster bolt and threaded rod. Finally had to bend it apart to get it out.

There was also some big spacer that fell out from the upper bolt that was a pain getting back in.

2 of us took 3 hours to finish, but now works great.

Thanks for feedback..

[P.E.Haiges]

Mr GF,

How far can you drive with the alternator working, try 7000+ miles.

I made its all the way back from Alaska to PA without the alternator working. I had a battery charger with me so I just charged the battery overnight to get engine started in the morning.

I couldn't have done that with a gasser!

Of course I had to drive with all the accessories off. Only the brushes were bad, but I didn'tknow what then.

Now I carry a spare voltage regulator with new brushes in it. If the regulator from your original alternator is still good, you might do that too. Its an easy fix.

P E H

[Ken300D]

Mr PEH,

Please take a picture of your trunk someday and post. We'd all like to see your inventory.



Ken300D

[adamb]

I had the pleasure to meet PEH and he is a very resourceful person indeed.
Very knowledgeable, kind and very much an adventurer. His trunk was filled with anything you could imagine, to make repairs and to be self reliant in the event of breakdown.
He definitely gets every bit of life out of his cars and I have learned from him as I was the complete opposite almost, changing stuff pre-emptively when not yet necessary. I know wait until signs of wear and end of life has been reached, provided there isn't the potential for chain affect of catastrophic loss.
Thaks PEH,
Adam Bush

[Mr Goodfahrt]

Thanks for the suggestion. One advantage to buying from a "recycler" is that you don't have to deal with a "core charge" and can keep the original. I did pull out the voltage regulator as a spare... looked OK.

Does anyone know how to restore or rebuild an alernator? I would like to fix this one if possible. Any DIY sites on this?

Thanks again all!

[81Wagon]

Originally posted by Mr Goodfahrt
Does anyone know how to restore or rebuild an alernator? I would like to fix this one if possible. Any DIY sites on this?

This site might be helpful to you:
http://www.mtmscientific.com/rewind.html