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Old 05-31-2007, 01:41 PM
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Another alternator question

I have an '86 chevy truck with ( I think ) an 85 amp alt. Serp belt, plastic fan.

this past weekend, we were out of town and I had the A/C on and glanced down at the volt meter (factory). It was sitting at 12v for about 5 seconds, then jumped to just a tad over 13v, then back to 12, back to 13, and so on. This went on for the entire rest of the trip home, about an hour. Although this truck and alt are 21 years old, it only has 34,000 original miles. I've cked the battery connections and alt connections. Nothing visibly wrong.

Any ideas? Regulator taking a dump? I don't want to trade this in for some POJ from AZ or Checker but would like to just fix it since it's so "new"! LOL

Mark

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Old 05-31-2007, 02:50 PM
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my dad's boat has a Delco alternator on it. does that same thing. bounces from 12- 16 all the time. probably the internal reg we figure
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Old 05-31-2007, 03:49 PM
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Quote:
Originally Posted by Jmark
I have an '86 chevy truck with ( I think ) an 85 amp alt. Serp belt, plastic fan.

this past weekend, we were out of town and I had the A/C on and glanced down at the volt meter (factory). It was sitting at 12v for about 5 seconds, then jumped to just a tad over 13v, then back to 12, back to 13, and so on. This went on for the entire rest of the trip home, about an hour. Although this truck and alt are 21 years old, it only has 34,000 original miles. I've cked the battery connections and alt connections. Nothing visibly wrong.

Any ideas? Regulator taking a dump? I don't want to trade this in for some POJ from AZ or Checker but would like to just fix it since it's so "new"! LOL

Mark
Although this is an older post here's some useful and related info.

As far as age goes, the Navy did a study of electrical/electronic equipment some years ago that compared MTBF (Mean Time Between Failure) rates of identical equipments that were in use shipboard and warehoused as spares. They found that the warehoused equipment had a failure rate nearly the same as shipboard of the same age. The conclusion was that most failures result from corrosion that occurs between dissimilar metals such as tin/lead solder and copper conductors in joints and that this is more related to age than to use.

So even though this alternator has but 34,000 miles on it; it's still 21 years old and should be experiencing failures that one would expect of an alternator of that age.

Bogie

Last edited by oldbogie; 05-31-2007 at 03:57 PM.
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Old 05-31-2007, 04:58 PM
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Doc here,

Sounds like either the diodes are breaking down on the regulator, or the brushes/Followers are going south..

You can get a rebuild kit for this, and do a general cleanup of the alternator for about $15.00 and a few hours of your time..

Kit has all the parts you need to get some more useful miles out of it if the unit isn't powder corroded throughout..New rectifier Diodes, New Regulator Diodes, New Brushes, New Spring followers, new bearings, or bushings..add some time at the coin op car wash degreasing and drying it, and some bench clean up & assembly and you should have a serviceable unit..

Doc
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Old 05-31-2007, 06:24 PM
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Thanks everyone. this thing is squeeky clean, the frame still has the crayon marks from when it was built! LOL

Guess i'll get some parts and go through it. Need to change the water pump too, it's also the original one. It's a pain to work on with dual air pumps and a mile of vac hoses......oh well, another project.

Mark
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Old 06-01-2007, 06:57 AM
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Check to be sure the tensioner is not frozen or sticky. This is a common issue and will cause the belt to slip and the voltage to drop.
I have seen this many times
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