1971 LT-1 Alternator Overcharging

[Shane S.]

Good Afternoon,

I am new to this. This is my first forum post. Tim Gilmore told me this is the way to best try and solve a problem that has us all stumped.

I have the original AC Delco / Remy 1100950 42a alternator. When I drive or sit and rev the motor the needle on the battery gauge goes quickly to full peg right at +40. I took the alternator and had it checked and then had it professionally rebuilt. Reinstalled and the same problem. I bought a over the counter alt which is a 61amp and it seems to work fine. I had the original retested and was told it was functioning pro[erly but they replaced the regulator again just for good measure. Reinstalled and same bad result.

I then bought the same model alternator online and installed it. Again, the needle moves way right when revving the motor.
both the original and the online purchase have been rebuilt and are now 65amp and not 42. I am told the parts are no longer available to rebuild a 42a to original amps. ??

I took an original 42amp (Never Rebuilt) alternator off of my 70 and installed it on the 71 and it works perfectly.

My battery is strong.

Sorry so long but. it has been a journey with this Red Devil of a 71 LT-1.

Thank you in advance,
Shane

[Edward J.]

Re: 1971 LT-1 Alternator Overcharging

Shane, why not try the rebuilt alt on your other car and see what happens?

[Shane S.]

Re: 1971 LT-1 Alternator Overcharging

Just tried you suggestion. The rebuilt alternator caused the battery needle to peg right as well. So now we know that it is the built alternators. Maybe someone can tell me why the rebuilt (now) 65amp alternators cause the battery gauge to go hard right when revving the motor.

Thank you Edward for you suggestion

[Edward J.]

Re: 1971 LT-1 Alternator Overcharging

Shane, generally speaking the major components do not always fail,rebuilders replace things like brushes, diode trio, regulator, and sometimes the rectifier bridge, bearings. I know that most parts are interchangeable for that style alternator, but it almost sound like the regulator is finding a ground, there is a (D) cutout on the back of alternator rear housing that when the tab on regulator is grounded will make the alternator charge.I am wondering if something is up with that tab touching the metal housing? Another thing is it possible someone has installed a regulator that by-passes the two wire plug with the exciter and 12 volt ignition wire? I would take the original to another rebuilder and tell him what’s up,if all else fails.

[Bill B.]

Re: 1971 LT-1 Alternator Overcharging

As a retired Electrical Engineer, you might want to perform the following simple troubleshooting suggestion:

Place a digital voltmeter across the battery terminals. Record the voltmeter reading and your ammeter gage indication at idle, 1,500 2,000, and 3,000 rpm. Post your results here or PM/email me.

I assume your battery is good, but, you might want to substitute another battery just to eliminate an internal intermittent battery issue.

Another possibility is an intermittent connection of the two-wire plug to the alternator.

[Tim G.]

Re: 1971 LT-1 Alternator Overcharging

Shane and I also determined that the pully on the alternator is smaller than the original pully for a 1971 LT1. The issue comes in when the engine starts winding up. He is going to try to replace the pully with a correct size pully.

Thank you all for helping out a new member.

[Duke W.]

Re: 1971 LT-1 Alternator Overcharging

Is the OE alternator an internal regulator type or external regulator?

Duke

[Terry M.]

Re: 1971 LT-1 Alternator Overcharging

Is the OE alternator an internal regulator type or external regulator?

Duke

Duke
The last externally regulated Corvette alternator (in stock configuration) was 1968. So the OE alternator for Shane's Corvette is internally regulated.

[Mark E.]

Re: 1971 LT-1 Alternator Overcharging

Shane,

Trying to understand what you've checked... is this accurate?


'71 original 42 amp- Pegs battery gauge on '71

'71 original rebuilt (now 65a?)- Pegs battery gauge on '71

"Over the counter" 61 amp- Okay on '71

'71 original w/new regulator- Pegs battery gauge on '71

"Online" 65 amp- Pegs battery gauge on '71

'70 never rebuilt 42 amp- Okay on '71

'71 original w/new regulator- Pegs battery gauge on '70

[Duke W.]

Re: 1971 LT-1 Alternator Overcharging

Duke
The last externally regulated Corvette alternator (in stock configuration) was 1968. So the OE alternator for Shane's Corvette is internally regulated.

Thanks, Terry. So here's my story, which may or may not be relevant.

For several years I fought an intermittent overvoltage situation with my Cosworth Vega. I finally traced it to a loose connector on the internal regulator (the smaller wire). And after diddling with the harness connector and even replacing it the problem would always come back.

I finally removed and disassembled the alternator and found the regulator spade was actually worn. With the regulator removed I could clearly see it. I replaced the regulator, and all was well, and I figured out why the spade terminal was worn.

As you may know four cylinder engines have a second order vertical shaking force that can be tamed with twin counter rotating balance shafts running at twice engine speed, but these only became common in the last couple of decades, usually on I-4s over two liters.

For over 15 years from the early eighties to the late nineties I ran the Cosworth Vega in track time event at Riverside and Willow Springs accumulating something on the order of 5-7000 miles with the engine running in the 3500-6500 range and sometimes as high as 7000. I calculated the maximum sinusoidal vibration to be +/- 15g at 233 Hz at 7000 revs. Every stamped steel part on that engine broke at least once and the vibration must have caused the harness terminal to wiggle on the regulator spade eventually causing enough wear that the connection became intermittent.

Cruciform crank V-8s have no unbalanced first or second order shaking forces or moments, so I would not expect the above issue to be common on such V-8s, but it's worth checking out. Take the terminals out of the plastic connector and make sure they fit SNUGLY on the regulator spades, and do so with the BATTERY DISCONNECYED because the large gage wire is HOT!

Duke