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Intermittent alternator operation #2931921
06/10/21 11:10 AM
06/10/21 11:10 AM
Joined: Jan 2003
Posts: 7,471
Minnesota
Hemi_Joel Offline OP
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Hemi_Joel  Offline OP
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Minnesota
Hi, on my '67 GTX the alternator operates intermittently. Sometimes it will work for 5 or 10 minutes then be off for 20 minutes or more. I replaced the regulator, that didn't do anything, I checked all the wiring and the grounds and that was okay. I brought the alternator in to a professional rebuilding shop and had it rebuilt. When it decides that it is not going to work, I can apply 12 volts to the field terminal and it does not operate.
What could it be inside this alternator that could be causing this? I want to have an idea before I bring it back to the rebuild shop, because most likely they will tell me it's not the alternator it's the car.

Thanks, Joel


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Re: Intermittent alternator operation [Re: Hemi_Joel] #2931932
06/10/21 11:36 AM
06/10/21 11:36 AM
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Posts: 10,666
North Dakota
6PakBee Offline
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6PakBee  Offline
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North Dakota
Replace the bushes.

Missed the fact that it was rebuilt. The brushes would have been replaced as standard operating procedure by any competent shop. Ignore my comment.

Last edited by 6PakBee; 06/11/21 09:52 AM. Reason: Missed that.

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Re: Intermittent alternator operation [Re: 6PakBee] #2931939
06/10/21 11:44 AM
06/10/21 11:44 AM
Joined: Jan 2003
Posts: 14,470
renton, Washington
ph23vo Offline
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renton, Washington
sounds like an intermittent open in the rotor...

Re: Intermittent alternator operation [Re: Hemi_Joel] #2931997
06/10/21 02:18 PM
06/10/21 02:18 PM
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UPPER MICHIGAN, MARQUETTE COUN...
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NITROUSN Offline
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UPPER MICHIGAN, MARQUETTE COUN...
Originally Posted by Hemi_Joel
Hi, on my '67 GTX the alternator operates intermittently. Sometimes it will work for 5 or 10 minutes then be off for 20 minutes or more. I replaced the regulator, that didn't do anything, I checked all the wiring and the grounds and that was okay. I brought the alternator in to a professional rebuilding shop and had it rebuilt. When it decides that it is not going to work, I can apply 12 volts to the field terminal and it does not operate.
What could it be inside this alternator that could be causing this? I want to have an idea before I bring it back to the rebuild shop, because most likely they will tell me it's not the alternator it's the car.

Thanks, Joel


When you field the alternator make sure there is voltage on the alternator stud. If you are losing the battery feed at the time you are fielding it the alternator will not put out.

Re: Intermittent alternator operation [Re: ph23vo] #2932001
06/10/21 02:41 PM
06/10/21 02:41 PM
Joined: Nov 2012
Posts: 86
Alabama
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WarEagle1 Offline
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Alabama
Originally Posted by ph23vo
sounds like an intermittent open in the rotor...

I've had an intermittent open like this in a square-back that drove me crazy. It happens. Many of these parts are antiques now.

Re: Intermittent alternator operation [Re: Hemi_Joel] #2932002
06/10/21 02:46 PM
06/10/21 02:46 PM
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Bend,OR USA
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Cab_Burge Offline
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Bend,OR USA
I'm going to assume it is a original single field alternator that should charge more than 12.8 volts when you turn the key on and the motor is running. What is the output voltage on the charging wire going back to the battery when it is charging?\
What voltage and amps does it put out on a test stand?"
I would look closely at the voltage regulator and its ground next twocents


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Intermittent alternator operation [Re: Cab_Burge] #2932080
06/10/21 07:26 PM
06/10/21 07:26 PM
Joined: Jan 2003
Posts: 10,486
Freeport IL USA
poorboy Offline
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Freeport IL USA
I would think its either not making contact between the bushes and the armature, or the connection inside the case at the main battery post is pretty weak.

The contact at the brushes could be either the brushes, binding (or broken, or weak) springs on the brushes, or a defective armature. if its a single field, you should have continuity between the field input and the ground while the armature is spun. A double field would have the continuity between the two field posts while the armature is spun.

Re: Intermittent alternator operation [Re: poorboy] #2932092
06/10/21 07:54 PM
06/10/21 07:54 PM
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nowhere
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Sniper Offline
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One would think that having the alternator rebuilt new brushes and such would have been included.

Re: Intermittent alternator operation [Re: Hemi_Joel] #2932181
06/11/21 03:30 AM
06/11/21 03:30 AM
Joined: Aug 2007
Posts: 6,089
Valencia, España
NachoRT74 Offline
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NachoRT74  Offline
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Valencia, España
What about if the problem is at bulkhead black wire getting into the cab? Alternator can be working but just power going anywhere, so no reading.


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Re: Intermittent alternator operation [Re: NachoRT74] #2932254
06/11/21 11:54 AM
06/11/21 11:54 AM
Joined: Jun 2014
Posts: 1,319
VA
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dragon slayer Offline
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VA
I guess I would replace alternator with known good one and see if it acts up in your car. You could put the suspect alternator in another car and see if it acts up. Divide and conquer. Is it the alternator or is it the car items.

To answer your question the diodes, rotor/brushes could be intermittent to cause your symptoms. Even a partial stator failure/diode failure and you could still get output just not full voltage. Loss of the field circuit would shutdown output. That is the brushes and rotor.

So if the alternator is fault, I would get the rebuild shop to do a better check of the rotor, or replace the rotor.







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