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generator system failure
Posted by: Peter Frantz ()
Date: July 03, 2018 01:45PM

This is a '64 Monza, semi-daily driver with a stock delco-remy generator. After 12+ years of trouble-free service, the generator system seems to have suddenly failed yesterday. When I drove to lunch from work yesterday it was fine, but when I fired up the car at 5 PM, the generator light stayed brightly lit. Since I've had such trouble-free use over the years, I haven't yet taken the time to fully understand and trouble shoot this system, so I need advice.

I started to run the diagnostics in the shop manual last night (page 8-3), but I'm afraid my cheap little ammeter can't handle the current (it has a 250mA limit). So I tried some of the voltage tests suggested by Frank and others in this recent thread. When I measure the voltage across the battery terminals, it is fixed at about 12.5 volts whether the engine is off, idling, or revving. When I measure from the armature to ground, it looks like zero volts, and when I jump the field terminal to ground, it still looks like zero volts from the Arm. Also, if I pull the negative battery terminal while the car is running, it dies immediately. That's about where I quit last night. I haven't yet tried to motor the generator, but I might try that this evening.

Here are some questions: 1) Is that enough to confirm that the problem is in the generator and not the regulator? 2) Does this kind of sudden failure (from excellent functionality to complete failure) tell anything about what component might have failed?

Also, I don't know if this is related, but I did some electrical work under the dash a couple days ago (radio power issues), and my right turn signal stopped flashing yesterday morning. Those two events might be related, but probably just a coincidence with my generator issues.

Thanks again for your help!
Peter

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Re: generator system failure
Posted by: vairchet ()
Date: July 03, 2018 02:11PM

It's possible generator brushes are worn out.

Chet in Ramona

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Re: generator system failure
Posted by: Peter Frantz ()
Date: July 03, 2018 02:19PM

Thanks Chet. That would be an easy fix. But I was thinking that brush wear would appear gradually. And since there are two of them, it seems like one would fail first, leaving the system just partially impaired. Is that wrong?

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Re: generator system failure
Posted by: joelsplace ()
Date: July 03, 2018 02:29PM

Both brushes have to work.
It does indicate the generator is not working.
They can work until they quit.
The motor test is not a sure thing. I've got one that passes that test but won't charge. If it won't motor it has a problem for sure.

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Re: generator system failure
Posted by: vairchet ()
Date: July 03, 2018 02:40PM

Vairdeb's '62 Monza did exactly what you've described. Swapped out worn brushes with replacement equivalents and.... voila!, generator functions as new. Typically, generator brushes only last between 20 to 25 thousand miles, perhaps less.

Chet in Ramona

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Re: generator system failure
Posted by: Peter Frantz ()
Date: July 03, 2018 07:34PM

OK, I pulled the brushes out. They are, of course, badly worn. I've put well over 30,000 miles on this car, and who knows how long these brushes had been wearing before I came along. But they don't look broken or anything. Does this still look like a possibility?

Peter


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Re: generator system failure
Posted by: joelsplace ()
Date: July 03, 2018 07:36PM

I would say you found the problem. Not that the brushes themselves wouldn't work but the springs that hold them against the armature can't provide the proper tension when they are that short.

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Re: generator system failure
Posted by: Frank DuVal ()
Date: July 03, 2018 08:02PM

When you see the new brushes, you will see that these are worn veerrryyy short!eye popping smiley

These look not even 1/4” long.

And yes, your test of jumping the field terminal to ground proves the generator is the problem, not the regulator.

Frank DuVal

Fredericksburg, VA



Edited 1 time(s). Last edit at 07/03/2018 08:03PM by Frank DuVal.

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Re: generator system failure
Posted by: vairmech ()
Date: July 04, 2018 03:22PM

Ummm, Guys, this is a generator correct? GROUNDING the field terminal does nothing. You remove the field wire from the generator then put 12v to the field terminal. That will make the generator put out the max it is capable of and you will hear it in the engine speed and the generator will probably make some noise. If putting 12v to the field terminal of the generator does nothing then something is wrong with the generator.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: generator system failure
Posted by: 63Spyderd ()
Date: July 04, 2018 07:05PM

vairmech Wrote:
-------------------------------------------------------
> Ummm, Guys, this is a generator correct? GROUNDING
> the field terminal does nothing. You remove the
> field wire from the generator then put 12v to the
> field terminal. That will make the generator put
> out the max it is capable of and you will hear it
> in the engine speed and the generator will
> probably make some noise. If putting 12v to the
> field terminal of the generator does nothing then
> something is wrong with the generator.

Incorrect. The GM Delco Generator is the EXTERNALLY GROUNDED type. Grounding the FIELD terminal produces maximum output.

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Re: generator system failure
Posted by: Frank DuVal ()
Date: July 04, 2018 07:33PM

Ken, re-read the shop manual.

All the GM Delco generator systems I have worked on need the F terminal grounded for full output. page

Look at the internal schematic of the 61 shop manual page 8-4 Figure 8-2. The F terminal wires to a field coil which in turn goes to the other field coil, and then to the A terminal. The A terminal gets connected to battery positive when the cutout closes. Until the cutout closes, residual magnetism develops a positive voltage onto the A terminal from the armature.

It is most alternators that need + 12 on the F terminal to full field.thumbs up

Frank DuVal

Fredericksburg, VA

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Re: generator system failure
Posted by: vairmech ()
Date: July 05, 2018 06:18AM

OOOOPS, You are correct! All I can say is brain fart.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: generator system failure
Posted by: Frank DuVal ()
Date: July 05, 2018 09:19AM

Mine does that too!grinning smiley

Frank DuVal

Fredericksburg, VA

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Re: generator system failure
Posted by: Peter Frantz ()
Date: July 09, 2018 12:31PM

Just to follow up: those worn brushes were the problem. I installed some new brushes, ran the generator as a motor on the bench, mounted it in the car, did the polarization, fired up the car, and all is well.

Thanks again.

Peter

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Re: generator system failure
Posted by: junkman ()
Date: July 09, 2018 02:02PM

Probably should have had the armature turned, and the commutator undercut at the same time. New bushings might also be in order. You can do the repairs piecemeal, or all at once.

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