Alternator question

[rjn72]

I have an 87 v30 with a 454 tbi. My problem is when the truck is idleing at a stop in the yard with nothing on it does fine. I turn on the lights and put it in gear and take off down the road, still fine. I come to a stop sign, not fine anymore. The lights dim, the alt gauge drops from about 15 to about 10.5 - 11, and a belt starts squeling like crazy. I think the alternator belt. When I leave the stop sign the volts on the alternator won't come back up and the lights won't brighten up unless I stop and turn the lights off and let it run in park for about 1 - 2 minutes. I can speed up the process if I turn off the heater and radio also. The truck has 22 lights that come on when the light switch is turned on, not counting interior lights, so I know they draw quite a bit. I think it is probably an alternator that is not putting out enough, however I am not positive. Has anyone else here had a similar problem that they could have another idea or second mine if you think a bigger alternator would fix the problem. Thanks in advance for all the advice.

[qu1cks1lver56]

sounds like you need a new alternator.

[sailed2japan]

try spraying some belt dressing on the alternator belt, if that doesn't work, it may be time for a new belt. If the belt that is on there now looks well worn I would try a new belt before I put on a new alternator.

[wyattglock]

While you have the belt off, spin the alternator slowly and feel if it is grinding. If so, not matter what the output says, replace it. Mine was putting out 14.5 volts at idle, and when I took it off the truck I have never felt and alternator grind so bad! It sounded and felt like sand was in the bearing race. If it feels fine and the belt is good, test it with a multimeter. You can check across the battery while it is idling. You should be getting 14.4 volts roughly, if not it is in need of replacing. Shut the truck off and check the battery also, you should get 12 volts, plus or minus about 1 volt. Any more than that and I would replace the battery also.

[glhman222]

this sounds normal, when the alternator slows down it cannot provide enough power to run all these things at once, so the battery helps in and thus the lights dim because the battery is like 12.6v while the alt when running can produce as high as 15v normally, if this still bothers you try finding a smaller diameter alternator pulley to swap on there

[old Rusty C10]

id have the alternator bench tested including the internal regulator