# 1966 Alternator pulley size



## gtoguy389 (Jun 3, 2012)

I am wondering what the original size of the alternator pulley should be for the 37 amp 1100704. The car has factory power steering, not sure if that makes a difference, with all original crank, water pump code XF, and power steering pulleys. The car has no power options and originally came with the 37 amp alternator. I have a 37 amp alternator date coded to put on the car, it currently has a 55 amp. I've noticed the pulley on the 55 amp has a smaller pulley, roughly 2-5/8" diameter, and the 37 amp has roughly a 2-7/8" diameter. I say roughly because I have not taken the pulleys off the shaft to get an exact measurement. I know the factory used different water pump pulleys for options like A/C, is that the only thing that would have determined the pulley size for the alternator? I guess what I am trying to ask is if the larger pulley is correct for my car, should the 55 amp been running the larger pulley? I want to do this the right way and learn a little something along the way. Thank you very much.


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## PontiacJim (Dec 29, 2012)

gtoguy389 said:


> I am wondering what the original size of the alternator pulley should be for the 37 amp 1100704. The car has factory power steering, not sure if that makes a difference, with all original crank, water pump code XF, and power steering pulleys. The car has no power options and originally came with the 37 amp alternator. I have a 37 amp alternator date coded to put on the car, it currently has a 55 amp. I've noticed the pulley on the 55 amp has a smaller pulley, roughly 2-5/8" diameter, and the 37 amp has roughly a 2-7/8" diameter. I say roughly because I have not taken the pulleys off the shaft to get an exact measurement. I know the factory used different water pump pulleys for options like A/C, is that the only thing that would have determined the pulley size for the alternator? I guess what I am trying to ask is if the larger pulley is correct for my car, should the 55 amp been running the larger pulley? I want to do this the right way and learn a little something along the way. Thank you very much.


Not sure what correct size is. Never checked and ran whatever pulley was on the replacement Alt when I used to go to the junkyards to get one. I would imagine that the pulley on the 37 amp Alt is original seeing it is date coded to your car as you generally do not pull them off for no reason. And if it were rebuilt, the same pulley goes back on.


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## O52 (Jan 27, 2019)

The 37 Amp pulley should be 2 3/4". In fact almost all the '66 Alternator pulleys are 2 3/4". It doesn't matter what amperage they are. Part # 1949357.
The only alt pulleys that are different are for the Air Injection engines. They are double groove and the diameter is 2 27/32"


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## gtoguy389 (Jun 3, 2012)

Thank you guys very much!! Awesome and much needed information. I searched the part # for the 55 amp alt. and it came back as either Buick or Oldsmobile. That is probably why it has a smaller pulley.


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