1980 alternator part number?

[Theo]

I'm looking for the correct part number for the alternator used on my 1980 L48. My alternator is either underpowered, or just needs a rebuild. It works "fine" when you don't ask too much of it, but put the lights, rear defog etc on, and it can't keep the voltmeter from dropping.
The one i have is no. 1102901 - 61 Amp. Is this the right one? Was there a higher rated one put on the 80?
If and when i do pull it apart for a rebuild, does anyone know where i can get rebuild parts, diode, rectifier etc from? Would rather rebuild than replace....
Cheers!

[John H.]

Re: 1980 alternator part number?

Theo -

The Spec Guide sez (assuming you have C60) that the original alternator (with C49) was #1101041 (70-amp) for an early car, or #1101075 (also 70-amp) for the 2nd design later cars.

[Theo]

Re: 1980 alternator part number?

John, thanks for the response...
Sorry, can you clarify what you mean by C60 and C49? Are these option codes of some sort? Excuse my ignorance(!)
My vette's build date is 7/80 (from memory, will check that) so I wonder if that classes it as late or early?
The main fact is that whatever the number, it should be 70 amp! This may explain the lack of grunt when i load it much....

[John H.]

Re: 1980 alternator part number?

Theo -

C60 is air conditioning, and C49 is the rear window defogger. A 7/80 build date would definitely make it a "late" car; the last 1980 was built on August 22nd.

[Joe L.]

Re: 1980 alternator part number?

Theo-----

The alternator that you have is a Series 10 SI. The original alternator for your application was, I believe, a Series 12 SI. I think that a remanufactured alternator available under GM #1984272 or Delco #321-140 will provide a SERVICE replacement equivalent to the original. This unit WILL NOT carry the original part number on the case, but it will otherwise be similar to the original in configuration and identical in function.

[Theo]

Re: 1980 alternator part number?

Thanks John-
Yes, i have both of those options. So I'm looking at the second of the two part numbers you provided....
I still need to see if my alternator is actually providing its "advertised" 61A, as who knows, it may still have the potential to provide enough power after a rebuild, even if not completely correct. I'm no expert on this to say the least, but I will test it as soon as my engine is running again.

[Theo]

Re: 1980 alternator part number?

Hi Joe,
I was reading about the 10 SI series alternators earlier today. Unfortunately my car's previous owner saw fit to buy a chilton's manual for '63 to '79 vettes! Obviously from a garage sale or similar. So there were no part numbers listed for 1980, which is a bit frustrating.... The 10 SI was quoted as being the "latest" design in that manual. So did the 10SI discontinue in 79 then?

The corvette action centre website has alternator part numbers for all c3's. Strangely, the number on my alternator is not listed, except for a 79 car with aircon, but that number is one digit different. Possible that their listing has an error, or do you think the part number on mine suggests it's from another car entirely?
Could you suggest where i might find out exactly what car/year my alternator was actually intended for?

Thankyou!

[Joe L.]

Re: 1980 alternator part number?

Theo-----

Your GM #1102901 alternator case originally resided on a 1978 Buick or a 1978-79 Pontiac. There's no telling where the "innerds" originally resided since they may have been swapped out by a commercial rebuilder. This part number was, indeed, a 61 amp unit.

The 10SI was not "superceded" by the 12SI. Most Delcotrons in the 37-63 amp range from 1969+ were 10 SI. These continued to be used in some GM applications through the 80s. The 12SI came into use about 1977 for 70 amp alternators and the 15 SI about the same time for 80 amp alternators.

If you existing 61 amp unit is having a hard time keep up, I don't think that's going to improve a lot after a rebuild. I'd replace it with a properly sized unit. These alternators aren't all that expensive to purchase as rebuilt units UNLESS you want one with the proper "numbers" and "dates".

[Theo Law]

Re: 1980 alternator part number?

That's quite interesting...
I wonder if that casing made it's way over to the UK seperately, or was put on since the car was imported?
At least i now know what it actually is!
So the numbers 10SI, 12SI, etc refer more to the actual power rating of the model, and don't represent a consecutive sequence - ie they existed at the same time.

As for what to do with mine now, I'm in two (or more!) minds.
First things first, I'll test the alternator's max output under load. If i find it's seriously under its claimed 61 amps, then there might be some point in doing a rebuild, even though its not the right part, it would be the cheapest option.
Or there's the new (70A) alternator path, like you say, they're not too expensive. Although if i want to go Delco, things can get a bit pricey with shipping to the UK - it's a pretty heavy lump!
My final option, I guess, is to look out for a genuine "period" 1980 alternator over here, and treat it to a rebuild myself. May well work out cheaper than a "new" Delco.

Thanks very much for the advice and info, Joe and also John - you've both put me firmly in the right direction...
Cheers!

[Joe L.]

Re: 1980 alternator part number?

Theo----

Yes, the 10SI, 12SI and 15SI refer to the basic "model" of the alternator. The 10 SI did come out first, but later "co-existed" with the others as they were introduced. Externally, each of these models has a successively larger and differently configured case than the others. The higher output models were introduced in order to meet the growing electrical demands of cars and trucks.

You don't have to neccessarily go with a Delco rebuilt unit. If there are other suppliers of rebuilt units in your area, just have them cross-reference a unit from the numbers I provided. Just about any rebuild will be from a Delco core, so you'll still get an original configuration unit.

It's hard to say when your unit got "exchanged". It's had about 23 years for it to happen, depending upon when you got the car. You can further confirm the "heritage" of the one you have by the date code. This will be a stamped-in code near the part number. It will be a number, followed by a letter, followed by 1 or 2 more numbers. The first number is the last digit of the year of manufacture, the letter is the consecutive month of the year (e.g. A= January), and the last digit(s) are the day of the month. Please post what you find.

[Theo Law]

Re: 1980 alternator part number?

Ok, I'm going from memory here, but i think the date code is 7A or 5A - I'll have to have a look when i get home. Perhaps it's most likely to be 7A - jan 1977. That might fit with what you have told me so far. I'll check on that though.
We don't have Delco stores in the UK anyway, so it would need to be shipped over if I was to replace it with one of them. That's where the big money starts to accumulate. I bought some parts from Ecklers recently, and the shipping has cost me about 70 dollars. The parts cost about 60 bucks! Quite annoying!
That's why I'll possibly keep an eye out for a used original 12si to restore. I'm not 100 % fanatical about originality on my vette, as perhaps too much has already been changed for me to get it factory fresh. However, I see no reason why i shouldn't try to keep it as original as i found it - i've only had it one year so far. Engine internals i have no problems with modifiying, but "external" appearance - interior and ancillaries - i think should be as stock as poss. (You might call me a hypocrite if i tell you it was resprayed from brown to red about 5 years ago!) I think i can afford to take my time looking for a proper unit, even if it turns out to be a wild goose chase, since the present unit only really complains in the dark and damp (ie lights and defog) weather, and that's (hopefully) a few months away yet!
I'll let you know what date codes i find tonight.