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Low Alternator output at idle

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ddfarm View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/02/2011 at 7:18am
it is  a motorola alt
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/02/2011 at 7:43am
You may have a;
Bad diode,
Bad stator winding,
Bad brushes
All or any combination of the above.
You can check the isolation diode pretty easily with a voltmeter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/02/2011 at 3:55pm
Okay I took the reman alternator back and replaced it with a new one. Still the same problem, at 800 rpms lights dim considerably and the meter in gauge cluster goes below the middle line(discharge). I have also checked the volts with another meter and get the same result. So could this be in the regulator? Or eventhough I have checked all the connections, could this still be a problem?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote poormansMACHINE Quote  Post ReplyReply Direct Link To This Post Posted: May/02/2011 at 4:13pm
The voltage drop numbers aren't abnormal and neither is the dimming of the lights.
It's not a late model with a 150 amp alternator.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/02/2011 at 4:23pm
Not the regulator if the thing charges at the correct voltage at speed.
Too large a pulley? What size pulley is on that thing?
You should sit and idle at higher voltage, however, if you turn the headlights on and esp bright, you will drop to 12.6v or so normally.
Maybe you are used to modern cars with halogens and all the modern junk?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/03/2011 at 7:54am
Outside dia of pulley is 2 5/8 inch. If I were to change to a 2 3/8 (1/4 inch smaller)would that make a considerable difference? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/03/2011 at 8:03am
Originally posted by ddfarm ddfarm wrote:

Outside dia of pulley is 2 5/8 inch. If I were to change to a 2 3/8 (1/4 inch smaller)would that make a considerable difference? 


Smaller pulley would spin the alternator faster. Might help.
BTW - what was the idle speed again? Is the idle too low?
Is the belt slipping? A worn/glazed or loose belt will dim things at idle.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2011 at 8:32am
Okay, I am still having the same problem at idle. The voltage across the back of the alternator at 800 rpms is still 12 volts with lights on and the lights are dim. If i speed up the lights brighten. I have changed the alternator and voltage regulator with no change. I must assume that it is in the wiring. So where do I start in the wiring. I know the grounds are good at the cross member and the firewall ground. If you need additional info on my diagnosis, check previous post,
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Post Options Post Options   Thanks (0) Thanks(0)   Quote poormansMACHINE Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2011 at 8:40am
You want it to operate like a late model then rip it out and convert to a late model high output alternator.
The car isn't broke. This is how it was in 69.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2011 at 8:17pm
Thanks for the observation but this is not how a 73 Javelin should act. I have had javelins since I was in high school ( since 71  ) and none have acted this way. Not sure how many you have had. I have bought them new off the lot and also used, but never had one act this way. In fact I currently have a 1971 Javelin that I restored 10 years ago and I do not have this problem. It has a stock alternator too. Maybe that was the way is was in 69 but it was not that way in 1971!
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