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Discussion Starter · #1 ·
I have a 1968 SS that at an idle the volt meter reads 15-17 volts then when the rpm increases the voltage drops to 13.5 to 14.5. I installed a new alternator, battery is good, and the voltage regulator is only a year old. Everything was fine until I went for a drive in early January and have been trying to figure out what is wrong. Any help will be much appreciated. Thanks in advance.
 

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Could the belt or the pulley be slipping ?.

I've seen tight belts slip on pulley's as well as the pulley slipping on the shaft of the alternator itself.

Your issue reminds me years ago when I had a chrome plated pulley on my alternator and when I was driving out of town at night I though I was going blind as the dash lights kept slowly getting dimmer and dimmer so I pulled to the shoulder and left the motor running and the lights slowly came back up to full brightness. I looked and the belt was not flapping or anything with the motor running so I then got back on the road and after a little while the dash lights again started getting dimmer and dimmer and I was afraid to turn the motor off thinking I would not have enough power to restart the motor, so I carefully snuck in some sandpaper under the belt to roughen it up and this worked until I got to my destination.
Once there I shut the motor off and the belt was indeed tight but the chrome and belt were so polished, no amount of tension would keep them from slipping against each other. I was also able to grab the blades on the alternator and with the motor off, spin the pulley with the belt not even stopping it.

I removed the pulley, put on a stocker and never had that issue again.

I've also seen the nut holding the pulley to the alternator shaft not be tight enough to where the belt and pulley are not slipping but the pulley to the alternator shaft is.

Jim
 

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15+ volts and you'll be "boiling" your battery in short notice.

Things to check right away:

The accuracy of your meter.

The external voltage regulator's mounting frame has a good, tight, clean metal ground connection to the radiator support sheet metal.

The small pigtail from battery (-) to the fender/front sheet metal is present.

The alternator mounting is tight and clean.

The battery terminals are clean and tight.

What kind of voltage regulator? Most have converted to the more reliable Wells/Duralast VR-715 available at AutoZone. This is a fully electronic unit. Most general replacements mechanical units are not built to proper original specs.
 
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