3G alternator with U/D pullies

Well, after much talk and little action, I finally motivated myself to do the 3G alternator swap yesterday. I bought a used 3G alternator from ebay for $50, which came with the harness so I could cut the stator wire off. I used 4 gauge wire without a fuse (temporary).

It charges better than the brand new 2G alternator I had, but not much. It can run the headlights just fine at 750 RPM (idle) but with the defrost and heater on full blast, the headlights will dim and voltage will go down. But if you give it a little gas and raise the RPMs up to about 850, it seems to have no trouble keeping up with the accessories.

I do have underdrive crank and waterpump pullies, but I have the 1 7/8" pulley on the 3G alternator. (is that stock on a 3g?) I noticed that the alternator's pulley had in and out play of about a 1/16th of an inch. And when you spin it, the bearings make an inconsistent hiss, leading me to believe they were well worn. The alternator is about 10 years old I believe. I took it to autozone, and it tested great! I think it was putting out about 160 amps or so at speed, but obviously it wasn't doing so great at idle.

Is it possible that the alternator could have lost its ability to make decent low RPM amps but remained just fine once it got spinning?

Can everyone with U/D pullies and a 3G alternator please give me some input on how well theirs worked? I'm not sure if I just got a bad one, or if they're all like this.

Thanks! (sorry this was so long)

Hmm. Where do you test for how much voltage the alternator is putting out? At the battery? I'd still like to hear more experiences with this though. Thanks for the input!

Has anyone ever heard of an alternator making crappy low speed voltage but still making plenty voltage once it gets really spinning?

I meant excessively lower than a normal alternator's voltage at low speed, and then picking up to about the normal alternator voltage at high speed.

90mustangGT said:

With the lights on, fan on, and HVAC fan on, mine doesn't charge so well with underdrives on a 160A 3G but above idle it puts out voltage like nothing is on.

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Is that with the 1 7/8" alternator pulley, or the 2.5 inch pulley?

I'm not sure if the alternator isn't performing properly, or what. Maybe I should just set the idle up about 100 RPM. How do you do this?

Sorry, one more question: Did the 94-95 alternators come with a 2.5" pulley stock or a 1 7/8"? Because the one I got had a 1 7/8" pulley, and maybe the guy put it on to cover up for the fact that the alternator wasn't working to potential. Any thoughts on this?