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Discussion Starter · #1 ·
I took a gamble and installed a set of Trick Flow underdrive pulleys and sure enough, my battery is not holding a charge. It was my first drive of the year (charged fine last year) and the reason I thought it would have been enough to keep the battery charged is my car is really stripped down (no stereo, wiper motor, etc.) My question is, I can't find the original alternator pulley I took off (probably pitched it) but have found some aftermarket billet pulleys which I would prefer anyways. I have found a 3 1/2, 2 3/4 and a 1 7/8. Firstly, can anyone let me know what the stock pulley size is (1993 Mustang 5.0) and secondly, is the larger the pulley preferred for better charging or the smaller???

I'd also like to mention my car only has an alternator, crank pulley, water pump and tensioner (no power steering, A/C or smog pulley.) I'm not sure if this would figure into the equation as well.

Any help appreciated. Thanks.
 

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The smaller the pulley the faster the Alt will spin, and the more it will charge. So, to help with your charging problem, put the smallest pulley you have on it. It doesnt matter that you have no a/c or p/s, that just effects hp and the length of your belt.
 

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Discussion Starter · #3 ·
Could the belt be slipping over the pulley if there is not enough tension on it? The reason I ask is, it seems that my tensioner (which is brand new) is reading at the low end of the tension gauge. It seems that there is a lot of play in the belt which I don't recall having when I had the old set up (with the power steering pump and old tensioner.)
 

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Belt slip would show up (if not squealing) as a low charge on the battery. You can overdrive the alternator but all that is doing is just spinning it faster.
It's not uncommon for some to have to get a new, slightly shorter belt when getting underdrives. I'd say get a shorter one, that should get more tension on the system. If the belt is old, it might be stretched.
 

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Discussion Starter · #5 ·
Belt slip would show up (if not squealing) as a low charge on the battery. You can overdrive the alternator but all that is doing is just spinning it faster.
It's not uncommon for some to have to get a new, slightly shorter belt when getting underdrives. I'd say get a shorter one, that should get more tension on the system. If the belt is old, it might be stretched.
It is a brand new belt. I purchased a new belt when I eliminated the power steering pump so it was a necessity. Would you recommend getting a smaller pulley and a shorter belt? Also, how much shorter of belt would you say?
 

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dude its your battery!! i know go have it load tested i bet you one cell is bad i had the same problem with batterys not holding a charege with under drives i have 2 subs sterio crap like the light s on heater and mine holds a charge i got a duralast gold 1000 ca 800 cca and never have a problem and the winter kills batterys and if you havent been driving it there ya go
 

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Discussion Starter · #9 ·
I installed a shorter belt and the problem is solved. Thanks for all the help. The belt must have been slipping over the pulley.

BTW, I keep my battery on a tender all winter and if I'm not driving it for longer than a two week period or so.

Thanks everyone.:bigthumbsup
 
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