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Discussion Starter · #1 ·
Hey guys so its alternator time and the reman I picked up today has a different size pulley than the pulley on the reman that is being replaced! :grin2:


New alt had a smaller pulley than what I have been running for the last x2 years. Maybe I have been using the wrong pulley or maybe it doesn't really matter?


Only problem is I don't really know what the correct size pulley is I should be using? It is not a huge difference between the 2.


2003 7.3l single alternator


Can anyone take a few minutes to measure their pulley diameter? It would be greatly appreciated. No need to measure at the ribs just the outside of the front of the pulley will do.


Thanks all!
 

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My 1999 7.3 single alt., measures 2-1/2", using a construction tape & hooking it on outside. Also I carry a spare alt that I had rebuilt & tested, & with a pulley. IIRC the alt guy had to swap out pulley size to match.
 

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Discussion Starter · #3 ·
Cool thank you. I should have posted this thread w measurements of both pulleys. I will measure what is installed on my van when I get to it.


Anyone else have anything different than 2.5"


My thoughts were higher output at idle w the smaller pulley as it would be spinning faster.
 

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Think about it for a minute.

Pulley size does not matter unless you run the engine at maximum RPMs or idle for long periods with lights, air and other stuff running.

Because in normal driving where your engine is changing speeds from maybe 1200 RPM to 3,000 RPM, the alternator is efficient at whatever RPM it is running at all of those speeds.

Unless the pulley is very large and your driving is mostly in town at very low speeds, I would not worry about it.

I am no tech. Just thinking at through.
 

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Discussion Starter · #5 ·
Spinning an alternator faster produces more current at a given RPM.


So idle to hwy crusing w 3.55 gears the alt will be putting out more w a smaller pulley at a given RPM than w a larger pulley.
 

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That is what I thought I said.

In any case, the regulator, computer and all that stuff can regulate it.

Otherwise when you are pulling a mountain with that heavy trailer and the RPM's are u[p around 3,000, bad thikngs would happen.

I can see where if the pulley was really too small and all of your driving is long distance at 75 MPH, the alternator bearings might not last as long as if it was turning more slowly.

It would be interesting to know if Ford uses a different pulley for trucks designed for high speeds on the highway and utility trucks that spend a lot of time idling with lots of lights and other electricals running, like power company trucks, etc.
 

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Discussion Starter · #7 ·
So what is the measurement of the pulley on your alt? :D
 

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I have no idea and really don't care because it maintains all of my truck at idle.

And it would not help the OP because he has a 7.3 with an entirely different electrical load and a smallger alternator than my truck.

Air conditioner in hot NC summers, lights, headlights, fog lights, trailer lights, keeps aux battery in horse trailer charged, big flashlight in tool box, ......

Never seen a light flicker.

That is why I said that I don't think the pulley size is all that important unless it was off the wall.

By the way, you could not find my alternator.

This on a 2012 with all of the options down to the sunroof.

Three trucks ago I had a '99 that on a hot summer night would dim the brights when the air conditioner waqs turned on and the truck was at idle.

But that had a lower capacity alternator.

By the way, Ford made it impossible for you to find my alternator.
 

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Discussion Starter · #9 ·
LMAO I am the OP.:headbang:


You had a 99 that the lights would flicker on at idle while running the AC. Sounds like you could have possibly benefitted from a smaller pulley on your alt.

@bork
do you know the output amperage of the alt on your truck?
 

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The equipment list is in the glove box, not here in the house.

But I think it is 200 amps.

I know it was the biggest that was available at the time I purchased the truck.

I don't recall what was on the '99

Sorry about missing that you are the OP.
 

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Sorry, I do not know output. Seems to be adequate for the dual ac and other factory stuff. If I park/idle for a real long time, with AC, especially in hot humid days, I'll turn on the AIC around 1100 rpms. It has charge protect, but I never use it.
 

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I have an eye problem that caused me toi miss the fact that the request about size was for bork.

It does not bother me when outside or driving, but it makes reading very tiresome and difficult.
 
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