what size fan belts for my a/c alternator pulley

[Lloyd Hammond]

Need to change my very old fan belts on my 383 with a/c and p/s. The two fan belts that work the factory a/c and alternator are Gates 7650 XL, which are supposed to be 65" circumference and 10mm (~3/8") wide. The factory specs say the belts should be around 64.5", so close. My alternator is all the way over toward the firewall suggesting the belts are far too long. I feel they could almost be 10" shorter. What belts are people running (lengthwise)?

Thanks in advance.

 

[pnora]

Gates 7640

 

[AR67GTX]

10” shorter is a lot to go shorter. Move the alternator back to where you would like it to set, pinch up the slack on one of your old belts and put a mark on both sides where it’s pinched together with a marker, measure the distance between the two marks and subtract that off your old belts dimension. Don’t go too short or you may not be able to get the new belt on to the pulleys.

 

[pnora]

What pulley is on your alternator? If the alternator has been replaced it could have a smaller diameter pulley. That would make sense that you are at the end of your adjustment with what seem to be the correct belts..

 

[Lloyd Hammond]

What pulley is on your alternator? If the alternator has been replaced it could have a smaller diameter pulley. That would make sense that you are at the end of your adjustment with what seem to be the correct belts..

Thanks for the advice guys. The car is 250 miles away so I don't have any great photos. I should have done what ARG67GTX and moved the alternator to where it should have been. The alternator appears to be the original unit. Maybe the pulley has been changed. These pics are ones I took years ago (not very helpful). I might just grab some belts of different sizes and see what goes.

 

[pnora]

Thanks for the advice guys. The car is 250 miles away so I don't have any great photos. I should have done what ARG67GTX and moved the alternator to where it should have been. The alternator appears to be the original unit. Maybe the pulley has been changed. These pics are ones I took years ago (not very helpful). I might just grab some belts of different sizes and see what goes.

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Pulley wise it should be a 3 inch. If its 2 1/2 its to small. Alternator is not original by that picture. So it may have the wrong pulley. If its working ok and you need more adjustment just find shorter belts.

 

[Dave6T4]

Go to Rock Auto website, and look up what belt they list for your application.

 

[Lloyd Hammond]

Pulley wise it should be a 3 inch. If its 2 1/2 its to small. Alternator is not original by that picture. So it may have the wrong pulley. If its working ok and you need more adjustment just find shorter belts.

I might see if I can get the correct pulley.

 

[AR67GTX]

Thanks for the advice guys. The car is 250 miles away so I don't have any great photos. I should have done what ARG67GTX and moved the alternator to where it should have been. The alternator appears to be the original unit. Maybe the pulley has been changed. These pics are ones I took years ago (not very helpful). I might just grab some belts of different sizes and see what goes.

View attachment 1799162

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I have 63.5” belts on my car but it has a round back alternator and I think yours may have a square back one. The adjustment bolt holes may be located differently in the cases. My pulley may be an oddball as it measures 2.7” dia.

My adjusting bolt is in the wrong hole I believe. It seems like I went with the shortest belt I could and the bolt holding my hoses did not quite reach the slot in the adjustment strap so I used the one further outside. I did this because these belts do a lot of flapping on the top run due to the distance unless I just tighten the heck out of them. Another 2” length and I could have used the other hole to bolt to the adjusting strap.