1972 Cutlass alternator/regulator question

[musicars]

Last fall the rear bearing in the alternator of our '72 Cutlass starting whining before a long out of state trip. I figured to be safe I would replace it with a rebuilt unit from the local NAPA. It seemed to work OK but occasionally it would make what sounded kind of like a bearing noise that would come and go. The lights also seemed to dim and brighten a tiny bit at idle. I put the car away for the winter and when I stared it up this spring the alternator was loud and then there was a loud pop as the side of the battery blew out. I immediatly put a volt meter at the battery posts and got a reading of 17.99 volts. I figure an overcharge caused a gas buid up that couldn't vent fast enough.
I now have found, after replacing the battery, that I can start with a reading of about 12.5 at the positive alternator post with the alternator sounding fine. Suddenly the alternator changes sound, the rpm may drop a tiny bit as if a load was being put on it, and the votage will jump to over 17 volts.
This has an external regulator on the firewall. Should I assume it is a regulator problem or could it still be the new alternator? Any suggestions or does someone know how I can test this before I start replacing things? Thanks.

[Oldsguy]

Yes, the regulator should be checked.

[musicars]

Any idea how to check it? I don't have an extra or I would simply switch it and see what happens.

[Lady72nRob71]

If one could be obtained at Napa or someplace locally, I would just replace it - it is a simple swap. The worse that could happen is that you end up with a spare, which may not be bad since it is mechanical and may need replacing later.

[musicars]

So I swapped alternators just to make sure it wasn't that and it still charged high. I picked up a brand new regulator and plugged it in. It buzzed like a seatbelt warning buzzer and the "GEN" light came on. Eventually the light was only coming on at about 2000 rpm and going out as rpm went up. The regulator keeps buzzing all the time and gets louder as rpm goes up.

I then grabbed an older regulator from one of the other cars and plugged that one in. Now the "GEN" light comes on when first started and there is a slight buzz. If I tap the throttle the light goes out and the buzzing stops but I noticed a slight flickering of the lights. The "GEN" light stays off until the car is restarted.

Any ideas? I've had a bunch of '65 - '72 GM cars with this general setup since I started driving in the '70s and never had a problem like this.

[BILL DEMMER]

i would recommend getting the solid-state replacement regulator that acdelco makes.

also check all of the connectors to make sure they are clean.


bill