3g alternator part #'s for v-belt idi's

[stick_witch]

Okay so there are about a million of these 3g swap threads, so I think I've got the details of the install covered. But, what all the threads seem to not address in much detail is what to get if you're someone who is ordering a new/reman 3g alt.

I know that for a 3g swap into an idi the alt from the 90s and early 00s 3.8L V6s fit, but other than that the details aren't really specific, except that it needs to be the 2 ear (& 12 & 6 o'clock) 8.25" spaced pivot style 3g alt, which is info that online retailers don't really advertise.

So I guess my question is, what model #'s work in the v-belt idi's? I know the 7756-3n-2g is a go-to standard, is there any others, or variations of? I'd get the 77563 but I can't seem to get it here in Alaska, but I see others that are similar with the serpentine pulley that are $90 that will ship, but no info regarding whether they're the small cased alt or the large cased alt...
How can you tell the difference between the 7" spaced small case 3g alt and the required 8.25" spaced large case 3g alt? The world of alternators is very foreign and confusing to me...

 

[ifrythings]

You will most likely have to swap the v-belt pulley from your old alt to the 3G alt as finding a 3G with 2 v-belt pulley isn’t as common as serpentine belt.

As for case size, you want the two hole version.

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[stick_witch]

You will most likely have to swap the v-belt pulley from your old alt to the 3G alt as finding a 3G with 2 v-belt pulley isn’t as common as serpentine belt.

Yeah thats kinda what I figure, the 7756-3n-2g is the only one I know of with the v-belt pulley. But, thats not a problem, I can swap them.

As for case size, you want the two hole version.

Ah yes! This is what I was looking for! Thanks a ton!

 

[franklin2]

There is a reason why you can't find a 3g unless it has a serpentine pulley on it. A single v-belt will not drive the 130 amp version to full output. Get ready for belt squeal.

 

[stick_witch]

There is a reason why you can't find a 3g unless it has a serpentine pulley on it. A single v-belt will not drive the 130 amp version to full output. Get ready for belt squeal.

Yeah, thats definitely a concern I have. But, there was a 3g with a 2 valley v-belt pulley that came stock in the 1992 and up 7.3 idi vans (in a 115 amp straight ear version and a side mount version). It was driven by only one vbelt and then drove the vacuum as well. Also, the 3g is total overkill anyway, so it won’t be operating at full output unless you have huge accessories, and for that reason you can cure any belt squeal simply by running a bigger pulley like a 2 7/8ths inch rather than the stock 2 5/8ths inch, which will drop the output curve and sacrifice the output potential of the alt for better torque reduction and more belt/pulley contact, which can totally be afforded.

But you’re totally right, that is exactly why the later idi’s switched to a serpentine layout and also why you can’t find vbelt 3gs, and if you plan to use the 3g to its full potential you definitely need to be running a serpentine belt. But, simply put, the 1g alts are just not enough to keep these things starting healthy if you idle a lot, take short drives, are in cold weather (like Alaska boy here) or use any extra accessories, and the 3g is going to be a much better cure for that than simply throwing in garbage 1g reman alts from parts stores every year and killing your batteries and starter because of weak power and erratic drain/charge cycles.

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[stick_witch]

Thanks guys for the responses! I did end up ordering an alt. Decided to go with a new 1995 mustang 3.8L 11:00 clocked alt from DB electrical with the serpentine pulley. Then I’ll just throw the 1g pulley on it with spacers and snug the belt up nice and tight and see how it does. Eventually I’ll probably switch to a larger pulley, and then maybe farther down the road I’ll do a serpentine swap if the current setup is having problems. But even then, it should be much better than sticking with old garbage 1g alts.....
I do like my trucks to actually start, not live on battery charger life support, and not eat starters for breakfast every morning a whole lot more than I like them to not squeal... shes an angry girl anyway, just let er’ squeal!

Also, while we're here talking about electricity... my batteries are shot too... what do you guys have in your trucks? Group 65s? Did you get group 31s to fit? What brand and models? CCA and CA? Might just make another thread.
Previous owner put Interstate MTP-24f 800cca's in mine... and as soon as it got cold they shat themselves

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[The_Josh_Bear]

There is a reason why you can't find a 3g unless it has a serpentine pulley on it. A single v-belt will not drive the 130 amp version to full output. Get ready for belt squeal.

I've heard this more than a few times over the years but I NEVER have belt squeal on my rig. I make sure that belt is nice and tight and I added an idler pulley to the long side but still just one drive belt. The other belt groove drives the vacuum pump.

 

[riphip]

Excuse me if I am mistaken.

Also, the 3g is total overkill anyway, so it won’t be operating at full output unless you have huge accessories, and for that reason you can cure any belt squeal simply by running a bigger pulley like a 2 7/8ths inch rather than the stock 2 5/8ths inch, which will drop the output curve and sacrifice the output potential of the alt for better torque reduction and more belt/pulley contact, which can totally be afforded.

Huh? 3G with original (1G) pulley charges at idle where the 1G had to be really spinning to charge (lightly)

ALT: 17425......Short belt from ALT to WP only (13A1080)...Eliminates vibration that long belt develops (not a Gold) to stop the squealing and belt jumping.

 

[stick_witch]

Excuse me if I am mistaken.

Huh? 3G with original (1G) pulley charges at idle where the 1G had to be really spinning to charge (lightly)

Yes, essentially. The 1g alt is rated only at like 65-100amps at 2000 rpms, where as the 3g alt is rated at 130 amps at 2000 rpms and more importantly at 90-100 amps around idle rpms. So the power output curve across all rpms on the 3g is significantly higher than that of the 1g.

In a diesel that idles and runs at very low rpms, its important that you have an alternator that can produce power efficiently and effectively at those lower rpms, especially if you have to run accessories like I do. (Cold + idle + blower to defrost frozen windows = RIP batteries)

As far as the pulley, since the 3g is kinda overkill, you can get away with sacrificing a little power output for less belt squeal with a larger pulley. A larger pulley will spin the alternator slower, but will give the belt more surface contact and a better, less strenuous torque ratio with which to spin the alternator.

ALT: 17425......Short belt from ALT to WP only (13A1080)...Eliminates vibration that long belt develops (not a Gold) to stop the squealing and belt jumping.

Yeah I’m also considering this. Although, I’d be cautious, you don’t want slippage between the other two belts and the water pump, and just not that by doing this you are putting more strain on the the other 2 belts driving the wp from the crank. But, I’d think 2 belts would be more enough to turn that water pump.


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[riphip]

No problem with mine over 10 years of use. But you do as you like. I did the experience, not the figuring. I will take overkill over under-performance always

 

[stick_witch]

No problem with mine over 10 years of use. But you do as you like. I did the experience, not the figuring. I will take overkill over under-performance always

Yeah for sure, thats where I’m at. Can’t understand why someone would go and buy 3 1g alts trying to fix their charging woes. Just get a 3g and be done with it. Im about to have mine so we will find out soon. Just gonna start with the stock pulley. If i get squeal, i’ll probably go to the smaller belt off the wp like you said.


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[riphip]

Some have tried adding an idler, which I did at first, but the long belt still presents a problem with vibration. I use the cog belts and have had good service from them.
Had a friend working in Alaska 1 year when it got to -80 windchill I think & he said everything was throwing serpentine belts everywhere on the highways.

 

[Garbage_Mechan]

I was able to pull the alternator harness off of a 96 F250 with a 460. Made the electrical part of the swap like factory. Upgraded the alternator to battery cable and provided the correct plug for the alternator. Only had to make one connection.
1 belt has not given me any squeal or other problems. Very worthwhile conversion!

 

[franklin2]

If your truck quickly starts and the batteries are in good shape, I can see where you would not get any squeal. The alternator is not going to full output.

You know they did make a 95 amp 3g version. That would be close to the same as the original 1G output and give better charging at low rpms correct?

 

[stick_witch]

If your truck quickly starts and the batteries are in good shape, I can see where you would not get any squeal. The alternator is not going to full output.

You know they did make a 95 amp 3g version. That would be close to the same as the original 1G output and give better charging at low rpms correct?

Yeah they did, but its rated much lower at idle, like 60 amps, which is pretty much the same as the 1g, but with the positive of being a more reliable unit. The 115 amp with the vbelt pulley was what came stock in some of the van and MD idi’s, which is the ideal alt to get for these, but are much harder to come by. People put the 130 amp 3gs in their vbelt driven idi’s all the time with little to no issues anyway, and if you do run into issues they can easily be fixed with a change in belt setup.
For me, the 130 amp is pretty necessary, especially in the winter here. Spend a lot of time driving in the cold and pitch dark up here in AK, so I’m running accessory led lights a lot, blower to defrost windows at idle rpms, and lots of hard cold starts when I’m hauling toys off the grid to get to my cabin and leaving the rig for days through sub 0 cold and snowstorms. Its my ride out of those places, so it absolutely needs to start without external power for starter and block heater when I get back to it.
In super extreme scenarios i might have some issues, but the majority of the time I shouldn’t, whereas the smaller alternators will be a headache constantly.
Would rather have the the performance potential of the 130 amp and get creative to mange any unintended consequences, than get something that is barely up to ***** for my minimum demands.


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