Help! Battery, Alternator, or somthing else?

[Bolisk]

When I bought my 1970 vette, I noticed that the alternator had a broken ear (where the bolts hold it to the alternator mount). It was fine and everything was working well. . .I just didn't like the fact that the ear was broken.

I was given a rebuilt and lightly used late 1969 alternator. . .and installed it in my car. The alternator was dusty but professional rebuilt and looked like new. I put it in the car and immediately noticed that the battery gauge would bounce around a bit. . .and the lights on the car would dim in and out. . .and the rpm would drop with every dim (only slightly).

After putting a couple of hundred miles on it the problem went away. I chalked it up to the fact that the alternator had been sitting in a box for a few years.

The next thing I noticed was that the radio was not noisy as hell. The previous alternator didn't do that. Anyone have any ideas?

Then my battery died, and I just replaced it with a new one. Now the battery gauge bounces all over the place (mostly in the +) range. . .but it's never consistent. . . if it drops in to the (-) range it's only by a hair. Having said that, every time the needle gets near 0, the lights dim and the rpm drops. . .

So anyone got ideas on where I should start. My gut feeling is that it's the alternator, and I need to rebuild it. . .but I want to get opinions before I order rebuild parts (anyone have recommendations on where to get the parts, and what I should put in the alternator to stop the radio noise).

Sorry, there were a bunch of questions in there.

 

[Bolisk]

WOW! 33 views with no responces! Did I stump everyone?

 

[navy2kcoupe]

When I bought my 1970 vette, I noticed that the alternator had a broken ear (where the bolts hold it to the alternator mount). It was fine and everything was working well. . .I just didn't like the fact that the ear was broken.

I was given a rebuilt and lightly used late 1969 alternator. . .and installed it in my car. The alternator was dusty but professional rebuilt and looked like new. I put it in the car and immediately noticed that the battery gauge would bounce around a bit. . .and the lights on the car would dim in and out. . .and the rpm would drop with every dim (only slightly).

After putting a couple of hundred miles on it the problem went away. I chalked it up to the fact that the alternator had been sitting in a box for a few years.

The next thing I noticed was that the radio was not noisy as hell. The previous alternator didn't do that. Anyone have any ideas?

Then my battery died, and I just replaced it with a new one. Now the battery gauge bounces all over the place (mostly in the +) range. . .but it's never consistent. . . if it drops in to the (-) range it's only by a hair. Having said that, every time the needle gets near 0, the lights dim and the rpm drops. . .

So anyone got ideas on where I should start. My gut feeling is that it's the alternator, and I need to rebuild it. . .but I want to get opinions before I order rebuild parts (anyone have recommendations on where to get the parts, and what I should put in the alternator to stop the radio noise).

Sorry, there were a bunch of questions in there.

Take to one of the local auto parts stores (Autozone etc) and have the alternator checked out. I believe that yours is an Internally Regulated alternator, and the regulator inside the alternator might be bad. They're not difficult to change out, but have it checked out before you start throwing parts at it. If the alternator checks out, then I would start looking at the wiring to see if you can find an intermittent short, bad contacts, melted wiring, or things like that. Maybe someone with more knowledge than I have will chime in with some additional ideas. Good luck finding and repairing the problem.
Andy

 

[TimAT]

There are diodes in the alternator (internal regulator like yours) any one of them could have died. There is a diode trio, and also a bridge. The bridge has 6 diodes in it, if IIRC. When a diode in that application dies, the current is not clipped correctly from a sine wave to a half wave. That will make the voltage/amp gauge act funny, but still charge the battery. Not as well, but it will still charge.
Look at the 2 wire connector at the case too- the wires tend to break at the plug. Intermittents are sometimes hard to find.

Both the bridge and the trio are pretty easy to change, but sometimes it's easier to get a rebuilt with a warranty.

 

[Vettehead Mikey]

Here's a rebuild how-to

Rebuilding a GM/Delco alternator

 

[LLC5]

When did GM switch to internal voltage regulators? I cannot remember off hand when GM switched. The OP has a 1970 vehicle and a 1969 alternator if I read the post correctly. The problems in his post could be symptoms of an incorrect alternator.

 

[BigJimZ16]

When did GM switch to internal voltage regulators? I cannot remember off hand when GM switched. The OP has a 1970 vehicle and a 1969 alternator if I read the post correctly. The problems in his post could be symptoms of an incorrect alternator.

If the two small wires in the plastic connector are edge to edge, it is an internal regulator; if they are face to face the external regulator is used. It is impossible, short of using a BFH, to accidently confuse the two.

 

[Vettehead Mikey]

When did GM switch to internal voltage regulators? I cannot remember off hand when GM switched. The OP has a 1970 vehicle and a 1969 alternator if I read the post correctly. The problems in his post could be symptoms of an incorrect alternator.

Don't know about the rest of GM's products, but on Corvette '68 was the last year for externally regulated.

 

[JohnZ]

Then my battery died, and I just replaced it with a new one. Now the battery gauge bounces all over the place (mostly in the +) range. . .but it's never consistent. . . if it drops in to the (-) range it's only by a hair. Having said that, every time the needle gets near 0, the lights dim and the rpm drops. . .

Sounds like the voltage regulator (which is internal to the alternator) has gone south.

 

[Hib Halverson]

If that's the case, changing the regulator in a 10SI is pretty easy.

The instructions are in the Service Manual.

 

[LLC5]

Don't know about the rest of GM's products, but on Corvette '68 was the last year for externally regulated.

Assuming then that the alternator is correct for the vehicle and the wiring harness on the vehicle, then the first step should be voltage drop checks on the positive and negative sides including tight and clean battery cables and bolts (just because a battery clamp bolt is tight doesn't mean that the clamp is also, always wiggle the clamp after tightening to make sure). If the battery load tests good, and the voltage drops and power feeds to the alternator are fine, then a problem exists in the alternator. Good luck with it.

 

[Phill]

try putting back the old alternator if you still have it and all that was wrong with it was a broken ear.

 

[SR'71]

you might try to measure the voltage drop across the ground cable.