Question for guys with underdrives

Jeremy_K

Registered User
Has anyone had problems with their charging system running underdrives? I'm hoping that it's related to my alternator power wire being hacked up so many times. I have a new wire on the way (discontinued by Ford by the way). I checked it with my voltmeter while it's running and it's only putting out 12.?? volts.:confused: When I had the stock pullies on there it was closer to 14V and didn't have any problems. I think I may be taxing it too much by running and IC fan and my low speed fan all the time in the summer. Anyone running extra accessories with underdrives with no problems? Can I get a better alternator than stock?
 
Underdrives can be a problem...

I have been running a set of underdrives for several years. Back when I traveled for a living on the highways, I never had any alternator charging issues. The underdrives provide full alternator charging at around 1000RPM's. Since I traded the road-warrior position for a desk job, most of my driving is stop-n-go rush hour commute to and from the office. I found that I was pulling down the battery because of the constant sitting in traffic at idle. This may not be a problem if you are driving more than you are stopped, but in my case I have a 30-mile commute that takes an average of 1.5 hours. I finally put the regular alternator pulley back on and haven't had any issues since then. So, in my experience, underdrives are just fine for normal driving, but not so good if you do the rush hour stop-n-go every day...
 
Like Larry said, you should be fine. I've had underdrives for about 10 years without any issues, except for the occassional stuck-in-traffic scenario and I noticed my headlights dimming.

I'd check your voltage with the car at about 1000 rpms and see what it is.
 
Cooling can be a concern as well... I have found that as long as I run the AC (which is a no-brainer in Atlanta during the summer), the low-speed fan keeps the temps down. A fan switch wouldn't be a bad idea with this setup.
I am thinking about moving back to the stock WP pulley and using a shorter drive belt so I can keep the ASP crank pulley. I just haven't gotten around to measuring for the correct belt length needed to use the smaller (stock) WP and Alt pullies with the smaller diameter ASP crank pulley. Now that I think about it, that would actually provide some amount of overdrive for the Alt and waterpump... If I could find a good stock size "zero balanced" lightweight crank pulley, I would probably swap out the entire setup. (Anybody got one they want to trade for a set of underdrives?)
 
Underdrives

My SC came with underdrive pulleys thanks to the previous owner.

When I had my alternator rebuilt earlier this year, the rebuild guy was moaning and groaning that the larger pulley wasn't doing the alternator any favors. He wasn't able to explain what that means.

I've noticed that due to the cam I'm running, sometimes when I push the clutch in when coming to a full stop, especially with the a/c on, the idiot light for the alternator will blink on.

Haven't had any cooling problems due to the water pump pulley and it's just about the size of a dinner plate - LOL.

Eddie

'90 5-speed SC
'97 LX with sports suspension
 
I was stuck in idle speed traffic for about a half hour the other day and it completely drained my battery to where I couldn't start it after lunch. I am rarely ever caught in traffic jams and most of my driving keeps the RPMs up around 2K. As far as cooling issues, I haven't noticed any so far. My car runs pretty cool even with the fan off. I think the fact that my header panel is hogged out between the headlights and the nice open cougar grill accounts for most of that. I've since bought a battery charger and just leave it plugged in overnight. I did some running around the city today with no problems. I think I'll just install the new alternator power wire and keep an eye on things with my voltmeter.
 
The only time ever my temperature went above "O" in NORM was after a long high speed run on a highway at WOT on a +30*C day.
 
I've seen that happen once to another car and we were litterally sitting at a stand-still for more than 40 minutes....with his stereo and headlights sucking down the battery fast. He was lucky that he had one of them smart batteries that shuts itself off when the voltage gets too low, so he was able to start back up. But he did have to sit through the rest of the traffice jam without lights and stereo.

fwiw, I was in the same jam and I don't remember having any problems, although I suspect I turned off my radio too.
 
Jeremy, I had just the crank and water pump under drive on my car. I was worried about the alt. being able to keep the battery charged too. You could just run the stock pulley and I don't think it would make that much difference horsepower wise.
 
Battery voltage

The pulleys may be a problem, I have never used them, :( so what others say will help. If you are only reading 12Vdc then you may be reading the voltage of the battery alone, which will be going down as you described. Sounds like the fuseable link from the alt or battery may be open (blown). I had that one bite me not long ago. Do your wire replacement, and check the other links by the EVTM before you make any hasty decisions about the pulleys :)
YB
 
yardbird said:
The pulleys may be a problem, I have never used them, :( so what others say will help. If you are only reading 12Vdc then you may be reading the voltage of the battery alone, which will be going down as you described. Sounds like the fuseable link from the alt or battery may be open (blown). I had that one bite me not long ago. Do your wire replacement, and check the other links by the EVTM before you make any hasty decisions about the pulleys :)
YB
Those fusible links have been a nemesis. We popped one by accident while doing my head gaskets with the battery connected:eek: I replaced it with an aftermarket fuse link. Then I actually fried and alternator at the track because the fusible link didn't blow like it was supposed to. Mine has been spliced and re-spliced a couple times and there's copper showing through the insulation from it rubbing on my power steering bracket.
 
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