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How do I figure out the right alternator belt I need for my '68 302? The AutoZone dipsh!ts have given me a different size each of three times, none of which are correct because my new Powermaster alt can't keep the battery charged for more than a couple days. I know it's not the alternator because it works fine for a few weeks until the belt starts to stretch, then drops in output.
 

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Try wrapping a string around the crank pulley up and around the alternator pulley. Tie it to make a loop. Take this loop to a NAPA store. They usually have a device that looks like a shoe sizer that they can measure the correct size of the belt needed. If your loop is a little loose, get the next size smaller belt.
 

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Autozone Dipshi*s...? You modify the engine by changing the factory alternator, walk into Autozone and expect them to magically figure out what belt you now need? Maybe it's time to re-examine your intelligence level. Most automotive belts are identified by a part number that is a direct reflection of their size. For example, a belt marked "745V4" would correspond to a belt that is 74.5 inches in length with a belt width of "4". Utilizing this newfound wisdom (if you can understand what I've explained), should enable you to figure out your own mess.
 

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Take the belt that is stretching and becoming loose to Napa.
Hand it to the nice gent at the counter and say "I need a belt that is .25 inches shorter that this one its too big for my application.

Pay the nice man for the new belt, take it home and install it on the car. Take your jack handle and wedge it between the alt and the block when installing to gets lots of leverage and pull it tight.
 

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So I assume the alternator is adjusted all the way out? There is quite a bit of adjustment on the alternator. If the belt you're using is too long, take it back to the nice folks at Autozone and politely ask for one that is an inch shorter. Surely you have that much adjustment.

But I'm not convinced that's your problem. I've never had a belt loosen up on me in a few weeks to the point of not functioning anymore.
 
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