Does someone have a spare Alt that they can tell me the shaft diameter?

I want to try and find a different pulley to speed up the Alt at idle.

The factory Alts (both the 70a and the 80a) are only capable of pushing 40a idling in gear at 600rpm. At 750rpm idling in park or neutral they produce enough to maintain system voltage with everything on.


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Just do the CS144 upgrade.


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Yea I know, but if I can put a 15 dollar pulley on and speed up the Alt a tad I’m all for it. I think a 57mm pulley will spreed it up enough.

Edit: I need to go down 2mm to speed up the Alt. I doubt I’ll find something smaller than 55mm


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This is what I was thinking.

It will increase rpm around 70-80. Its 15 dollars but I need to verify shaft size.




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I mean, you can.

But the CS144 is pretty much plug and play; and puts out 80-110 amps at idle (speed depending); which is what the stock alternator maxes out at.

I’d just do the CS144.


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I’ve got all the info to do the CS144 and have had one picked out on DB Electricial for a few years now.

Just never pulled the trigger yet.......


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$15 to $20 to try isn't bad at all. That just my be enough to get the rpms your after.

I don't have any Alts out at the moment or I get you that measurement of the shaft for you. :-)

I have a spare Alt at my house that my Ex is supposed to be out of by the 20th. Tomorrow I’m stopping out to do yard work and pick up the dogs for my 5 day off stretch. I should be able to get the info.


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Ok... If you cant let me know. I pull one off and check it for you.

I've often thought this would be a great idea, I have a hydraulic plow on my 97 which serves to plow only the drive way now, dual batteries isolated via a switch, without driving it on the Hwy and the short trips plowing I have trouble keeping batteries in it at -30*, looked at the high output alts, but I'm convinced charging at idle would be better/economical, and a smaller pulley would be the simple answer if you can get that nut off, perhaps a chain visegrip wrench and impact would do it, but you'll trash the factory pulley-no biggy I guess since it's being swapped. It really doesn't start charging until 1500RPMS if I recall correctly.

**That pulley pictured looks to have to many grooves though like a serpentine belt as per description although often confused, ours are only 4 groove belts.

Well I removed the pulley from my 70a Alt and got disappointed.

Shaft size is 15mm and I measured the pulley OD as 53mm. Plus it looks exactly like the picture I posted.

When I said the factory pulley is 55mm I was going by the specs on a website for a replacement Alt.

So I think my hopes are dashed. I haven’t found a 50mm pulley with a 15mm shaft size.


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Oh bummer. I was liking this idea.

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I’m bummed. Shy of making one on the lathe at work..........


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Do it! I'll buy your prototype. Surprised they dont have pulleys in all shapes and sizes.

Wouldnt be a bad idea to build one to see if your theory is correct?

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