Single vs double V-belt on 3G alternator upgrade - can someone clarify this for me?

[WMO4IDI]

I did my best to use the search function but couldn't find an answer...

My 1G gave out and I'm ordering a 3G alt, presently doing my homework on the belt setup and I'm getting confused.

Here's my setup at the moment on an former U-haul 1989 F350 Cab & Chassis. 1 belt goes to the alternator, another drives the vacuum pump and the 3rd one drives the power steering pump.

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From what I've seen on posts with the double V-belt pulley is that the 2nd groove (outward) is for a belt to drive the vacuum pump underneath, not a 2nd v-belt to help drive the alternator.

Am I getting this right?

Now, pretty much everyone says I'll get belt squeal if I leave it with a single pulley but I don't see why if the 2nd one drives the vacuum pump, the belt driving the alternator with have even more load on it?!?!

Wouldn't putting a slightly bigger single v-belt pulley solve the squealing issue by adding more contact surface (at the cost of a few RPMs)?

 

[WMO4IDI]

Complimentary picture of it's former life

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[IDIBRONCO]

Here's my setup at the moment on an former U-haul 1989 F350 Cab & Chassis. 1 belt goes to the alternator, another drives the vacuum pump and the 3rd one drives the power steering pump.

I haven't seen that set up before.

From what I've seen on posts with the double V-belt pulley is that the 2nd groove (outward) is for a belt to drive the vacuum pump underneath, not a 2nd v-belt to help drive the alternator.

Am I getting this right?

Yes. That's the usual set up and how it was done from the factory. Instead of the vacuum pump, that pulley groove normally runs the A/C compressor.

Now, pretty much everyone says I'll get belt squeal if I leave it with a single pulley but I don't see why if the 2nd one drives the vacuum pump, the belt driving the alternator with have even more load on it?!?!

It's because the 3G alternator will put more strain on the belt than the old 1G does. I'm doing just fine with a single belt on mine. I'm running a (Gates?) green stripe belt on it. I don't get belt squeal unless I put a large demand on the alternator. I'm also still using the factory charge wire that some people say won't work. The alternator does put out more of a charge than the 1G did so I don't feel like I'm limiting the alternator like some people say. I'm not recommending one way or the other. Just letting you know what I did.

Wouldn't putting a slightly bigger single v-belt pulley solve the squealing issue by adding more contact surface (at the cost of a few RPMs)?

I don't know about RPM, but it looks like you've already got a wider belt on the alternator. It should be the same width as the other two belts. Yours rides up higher in the groove than normal.

 

[WMO4IDI]

I haven't seen that set up before.

I get that a lot with this truck!

Yes. That's the usual set up and how it was done from the factory. Instead of the vacuum pump, that pulley groove normally runs the A/C compressor.

Yeah, no AC on this old gal.

It's because the 3G alternator will put more strain on the belt than the old 1G does. I'm doing just fine with a single belt on mine. I'm running a (Gates?) green stripe belt on it. I don't get belt squeal unless I put a large demand on the alternator. I'm also still using the factory charge wire that some people say won't work. The alternator does put out more of a charge than the 1G did so I don't feel like I'm limiting the alternator like some people say. I'm not recommending one way or the other. Just letting you know what I did.

I cut the wire just to avoid having battery drain from a bad diode bridge... it gave out and was glowing cherry red inside the alternator when the lights turned on in the instrument cluster. I'll just re-wire and add an ANL fuse on it.

I don't know about RPM, but it looks like you've already got a wider belt on the alternator. It should be the same width as the other two belts. Yours rides up higher in the groove than normal.

I meant a bigger diameter pulley...

I was wondering what the PO did there, probably a "good enough for now" replacement. The engine is one of the only parts I haven't worked on extensively, bodywork in the spring and then I'm hunting down an engine to rebuild.

 

[franklin2]

It's the simple fact that a single v-belt, will not transfer enough horsepower to run a 130 amp alternator at full output.

But luckily most people do not need the full 130amp output. And the few times they do, the belt will squeal some. You can consider it just "talking to you" letting you know you are putting a heavy load on it.

You will get better charging at lower rpms with the 3G. A larger pulley would negate this advantage some, I would keep the same size pulley.