So, driving around the last two days I've noticed some real strange (new) electrical problems. I'll be driving along at some RPM (doesn't matter what it is really) and the ammeter willl start bouncing quite radically from the discharge side to the charge side or sit on the discharge side for a while and then bounce to the charge side...

It does this for a bit, and then goes back to normal. Several minutes later, it will do it again. When it happens, the lights dim/brighten depending on whether it's on the charging or discharging side of the ammeter.

FYI, I have the original '69 alternator for an A/C small block in my car. It's internally regulated.

Is this my alternator (guessing regulator is going), my battery, or something else?

 

ttt

 

That happened to mine You need to rebuild the alternator. one of the diodes is shorting. Before going for the rebuild make sure you check all of the connections.

 

Bad diode. Just replace the whole alternator and regulator. Regulators were not meant to take AC and it's probably on its way out after the diode went. You may want to switch to a single wire alternator, it will probably be cheaper.
Gary

 

Just in cast that didnt work, my '69 did the same thing. replaced the alternator, 3 times! cleaned grounds, cleaned hots, pulled the dash apart, basically pulled my hair out. finally found it after all that and 3 months. the larger wire leaving the plug in the side of the alternator(the reference wire for the voltage regulator) had a hairline crack in the connector Pretty hard to see until it finally broke, cause i had removed the wires from the plastic plug to clean the terminals and didnt catch it, so it would heat up, or vibrate or whatever and the regulator would loose its signal and overcharge, then it would get its signal and undercharge. was a major pain in the rear. Cooked a new battery out of the deal too. changed the plug out and my problems went away, wish i had known it before i wasted all that time and money though!! hope that helped.

 

So, it would be a good idea to check all that? Also, would this cause sometimes starting problems?

Thanks! :smash:

 

starting problems? does it turn over and not start? or not turn over? clicking?

 

rainman -
A '69 doesn't have an internal regulator - '71 is the first year for internal reg's. If you have the original '69 alternator, you may have a bad diode. I have both positive and negative diodes brand new in a box. The alternators are very easy to rebuild - we can yank yours apart in a flash if you want to stop up to the house after the tech session on Saturday. I also have spare internal reg alternators and lots of other parts, so we can get you taken care of if you need it....

Hey.... there's an idea... A second tech session up at my house after the Paint Tech session: "How to Rebuild an Alternator..!" No problem as long as we don't run out of beer!! :cheers:


[Modified by lars, 8:43 PM 1/18/2002]

 

I'll pick some up on the way. Any flavor in particular? I know "not light, diet, fat-free," or any of that stuff...

Dave :smash:

 

Lars,
I think 68 was the first year that Chevrolet used an internal voltage regulator on a car, and it was the Corvette. The 69 also had the internal regulator, by 71 they had switched to internal regulators on all their models.
My first experience with an internally regulated AC/Delco alternator was in 1973 on a Pontiac Ventura (Nova), I was not impressed. It failed 3 times in 3 years.

 

Thanks for the correction, Smoke. In that case, I'll dig out a few internal reg alternators from my parts dungeon....

Rainman -
The most common thing to go bad in those internal reg alternators is the regulator itself. These alternators do not use individual diodes, but a diode trio and a bridge rectifier. We can test and verify all components except the regulator - we'll have to have the reg tested by a NAPA store with a reg testing machine. But this can be done....

 

Yeah...cause if I didn't have the internal reg...I'd wonder how it worked, 'cause there's no reg in the wiring harness... :yesnod:

But, I'll be up tomorrow for all the festivities. :smash: :cheers:

 

My 68 has the external alternator, and is factory, I'm quite sure. It has the plug for the regulator in the harness.

 

In the Corvette "line", 68 was the last year for the external voltage regulator. 69 was the first year for the internal regulator. None of the other GM line switched till a few years later, as others have said. That's what makes the 69 Corvette alternator a rare and expensive item. It has a unique case configuration, with "fins" on the back. There is no interchange with other Chevy or GM cars. If originality is your "bag", most definitely rebuild it. You will be amazed when you check the prices of original, numbered and dated, 69 alternators. Restored small block base alternators sell for $400.00 and up. Big Block 69 alternators...don't remember the "numbers" can fetch close to $800.00 :) Chuck

 

I did get to follow Lars to his house where we discovered the problem with my electrical system. He pulled out an internally regulated Caddy alternator (exact same case and rating, just a different part number)...and we hooked it up to see if it worked and fixed the problem. The first thing to note was that as soon as I stepped on the brake pedal, the voltage dropped from 12ish volts to 10ish volts. UH OH! :eek:

I started the car, and the alternator was charging just fine...albiet a little high 15ish volts. So, we looked for the voltage loss. It turns out that my positive battery cable had worked its way loose due to BUBBA making the bolts to hold the cables on the battery and not using correct ones. After Lars removed the somewhat welded together nut and bolt and put a shorter set on, we put my original (numbers matching) alternator back on.

Fired her up, charging at a respectable 14.8 volts...and no random voltage drop due to pushing the brake pedal. Also, my wild fluctuations on the ammeter were gone.

It turns out, the alternator was in perfect working condition, but would keep stepping up to a higher charging rate when it could "see" the battery, and then turning off when it couldn't. Or vice versa.

Needless to say, Lars worked his magic again, and even though I'm a El Engr major, I still forget the simple rules of keeping the magic smoke in the wires...You gotta have 'em hooked up first! :lol:

As for the drive back, the car worked great! Not a single light flickered or anything. Thanks again, Lars! :cheers: