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Old 09-20-2009, 07:39 PM
birdbrain birdbrain is offline
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Hello everyone. I went to a car show today and as I was parking I saw the generator light come on slightly. I reved the motor and it went out. When I was ready to leave I started the car and drove home(68 miles) when I got home I stopped the car and the generator light came on bright. I tightened the belt and it went out again. I charged the battery up for a while then took a reading on my multi tester. It read 12.80 then 12.59 I let it run for a while and it never went up or down however the light would come on and stay on, if I reved the motor the light would dim and almost go out. My question to the forum is how can I tell if the voltage regulator is going bad or the generator it self? Is there a test I can perform? Thanks in advance. Rodney
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Old 09-20-2009, 07:42 PM
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byersmtrco byersmtrco is offline
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Usually V/reg is on or off. It sounds as if the gen is just putting out @ low voltage. Do you have a local Starter Generator shop? Sometimes they can just throw a set of brushes in em and they're good for another 10 years.
John Byers
1960 Convertible (Orig owner)
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Old 09-20-2009, 08:05 PM
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JohnG JohnG is offline
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They would also clean up the brush holder area which gets crapped up with carbon over time. The brushes need to be free to move against the commutator. You might try just doing some cleaning first. I am not sure if you can do this with the generator still in the car or not. It only involves taking the cover off the end. I can provide a photo as I have a spare generator.

If you do take it to a shop, take the Regulator with you and they can test them as a pair for you.

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Old 09-21-2009, 03:15 AM
bird 60 bird 60 is offline
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Hi Rodney,

There's a chance that one of the brush wires are broken & not making a good contact. Or it could be one or both brushes are pretty well worn down. I don't know how long since the Genny was last repaired, but if it hasn't for a few years I would take it out. (1) Give it a good clean. (2) Get new brushes. (3) If the Commutator is out of round or slightly concave get it turned. (4) Get the Commutator grooves (Mica) cleaned 1/32" below the copper & then with #00 or #000 sandpaper remove any rough edges. (5) Check the bearings for slop & change them if required. (6) If the rest of it is O.K. it should last you for the next ten years or around 20,000 miles. Or if you're not a Purist now is the time to change over to an Alternator.

Chris....From the Land of OZ.
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Old 09-21-2009, 10:49 AM
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simplyconnected simplyconnected is offline
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Previous posts are correct about brushes. They're cheap (~$8/set of 4) but the idea is to change them before they fail. Do not run your generator if you are not sure the brushes are ok. If they stick or are worn out, they arc and burn the copper commutator segments.

You can test the generator by forcing it to produce full voltage (around 15-volts). Take the field wire off your regulator and connect it to BATT. The ARM voltage will increase to full volts. You can run this for up to two minutes, which should be plenty of time to troubleshoot. Either keep your lights off, during this test, or don't rev the engine real fast. Your meter should show when you approach 13.5-volts (nominal charging voltage).

Turn the headlights on for a while to drain the battery. If the regulator isn't sending armature current to a battery that is partially drained, you will know.

Your GEN light only comes on when the battery voltage is higher than your generator is putting out (like when you first turn the key on before starting your engine, or if you throw a belt).

All the current to charge your battery goes through the generator brushes. They should last for about 50,000 miles.
By contrast, an alternator has two brushes, but they only pass about one amp (to excite the field). Those brushes are much smaller and should last 100,000 miles. The whole brush holder w/brushes cost about $15. On Ford alternators, they are accessible from the back without removing the end-plate.

Hope this helps. - Dave
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Old 09-21-2009, 07:55 PM
vernz vernz is offline
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simplyconnected - I have a question about the procedure you discussed. My generator is putting out about 1 volt. I pulled it and found that a brush spring was broken and the arm that pushed down on the brush was loose inside the generator. I saw no damage to anything so I replaced the spring and put it together after cleaning up the commutator. I decided to try polarizing the generator by removing the field wire at theregulator and touching it to the battery connection at the regulator. It instantly became too hot to hold.....a lot of current flowing. In your answer below you talk about the same connection being made for up to two minutes. Does this indicate I have a shorted filed winding?

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Old 09-21-2009, 08:01 PM
tbirds8 tbirds8 is offline
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On our cars moisture gets to the bottom brush and it gets stuck in the holder. I've cleaned the holder and spring up a couple times and I'm startin to lean to an alternator. We don't drive these like we used to. (well everyday for me back in the day) You will need snow tires and chains!! .............Bill
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