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Old 03-12-2009, 05:02 PM
tsmith455 tsmith455 is offline
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Default GM Alternator Identification

I have several early GM/Pontiac alt's I have accumulated over the years and would like to know how to identify them. Most are open face, with different amps. I haven't located a good source for identifying them. Also, what's the primary difference between Pontiac, Chev, Buick and Olds alt's. These are mostly internal regulated, however some are external. When did GM switch over to internal regulated alt's and was Pontiac the only one to use the open face?

Example of the numbers on one is:

1100928 55A
1C5 12VNEG

Any help would be appreciated.

TS

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Old 03-12-2009, 05:52 PM
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Post numbers as I'm sure someone can help. Example is a March 5, 1971 assembled alternator for a Pontiac. The '69 Firebird was one of the first Pontiac cars to use the internal regulator, that I know of. And, I believe the Camaro and Corvette used the open face. Someone probably knows answers for sure.

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Old 03-12-2009, 06:11 PM
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How do you know its for a pontiac.....is that the 1 proceeding the C 5 or does the 1100928 provide any significance?

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Old 03-12-2009, 06:35 PM
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The 1 by itself is the year (1971). The 1100928 is the part number

If you search this Firebird parts related PDF you willl find the 1100928 listed. It's the 55 AMP alternator for Pontiacs with AC or rear window defroster or other options, but not all options or they bumped up to the 80 AMP alternator 1101015. If you had no options like those then you got the 37 AMP alternaot 1100927. The 927 and 928 are open face in 1971. The 1101015 is not open face.

http://thefirstgensite.com/library/partscounter/2-i.pdf

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1971 Trans Am White/Blue 4-speed limited options - Norwood plant
http://forums.maxperformanceinc.com/...d.php?t=757496
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Old 03-13-2009, 12:44 AM
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I would be interested in one or two open face (6 spoke) internally regulated alternators...especially if they have Olds part numbers. I can provide the Olds part numbers I am looking for. So--yes, some Oldsmobiles used them also.

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Old 03-13-2009, 08:31 AM
tsmith455 tsmith455 is offline
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Thank you all for the quick responses. TA455HO thank you for the attached link....exactly what I was looking for.

P Glade let me know what Numbers you are looking for and I will look to see what I have.

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Old 03-13-2009, 08:34 AM
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BTW....I believe these are (5 spoke) not 6.

TS

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Old 03-13-2009, 02:59 PM
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Let me do some digging here. I believe the Olds open face alternators were 6 spoke so please check the "spoke count" on yours to make sure. In the meantime I will get a number or to to send over.

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Old 03-13-2009, 05:37 PM
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Please see pic of the open face alt's I have.
Attached Thumbnails
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Name:	IMG_0845.jpg
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Size:	90.5 KB
ID:	161665  

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Old 03-13-2009, 07:03 PM
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That looks just like the 1100927s that I've seen. Do you have any 927 or only 928 number? In the 927 I'm loooking for a three (or four) digit date code of 0Gx or 0Hx. Anything like that? x would be any number from 1 to 31.

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http://www.ford-trucks.com/forums/11...-f250-4x4.html
1971 Trans Am White/Blue 4-speed limited options - Norwood plant
http://forums.maxperformanceinc.com/...d.php?t=757496
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Old 03-13-2009, 07:28 PM
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I'll see your 5 spoke and raise you by one spoke

6 spoke version:
Attached Thumbnails
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Size:	70.9 KB
ID:	161680  

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Old 03-13-2009, 08:12 PM
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This is 5 spoke draw. Your holding one too many and need to discard one.

Then you gotta ask yourself why the hell did Pontiac do it one way and Olds do it a different way? Two different molds for a 10si style open face Delcotron. No wonder GM is going broke...it all starts with the little things like this.

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http://www.ford-trucks.com/forums/11...-f250-4x4.html
1971 Trans Am White/Blue 4-speed limited options - Norwood plant
http://forums.maxperformanceinc.com/...d.php?t=757496
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Old 03-13-2009, 10:55 PM
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My thinking is they started out with 6 spoke open faces and then the beancounters started tinkering with it and they eliminated a spoke. I think some pre-70 Chevy's had OFA's (easier to type!) and I do know 69 442's used a 6 spoke. I have found 5 spoke OFA's on early 70's (70-72 I think) Buick Electras.

You are right....some of this stuff is absolutely crazy from a parts standpoint. SO MANY different parts used across very similar vehicles. Some was experimentation (Olds just used it on big block 442's/HO's for example) to test things like internal regulators (additional cooling needed thus the OFA).

On the other hand at least it keeps these different vehicles more unique.

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Old 03-15-2009, 12:02 PM
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tsmith455,
pm sent.

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Old 03-16-2009, 08:29 PM
tsmith455 tsmith455 is offline
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Spring break.....sorry for the slow response. 5 spoke vs 6 spoke ......certainly interesting. Learn something new about these cars every day. The alts I have are all 5 spoke. Didn't even realize they made a 6 spoke alt.

TS

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Old 03-16-2009, 11:00 PM
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possibly the 6 spoke vs the 5 spoke had to do with the different engines. This is just a guess,but with different mounting systems used on Pontiac vs Olds and the different charicteristics of the engines, possibly the 5 spokes were breaking on the olds so the fix was to add one additional spoke for strength?? I bet it has something to do with this.. Engineers are pretty meticulous and unlike stylist departments, they are more concerned with function over form.SO either strength, or the positioning of the alternators dictated additional spokes.. that is my guess, and it is nothing more than a guess..

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Old 03-19-2009, 10:52 PM
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I'm also looking for a 1100927 37amp open face alternator with a stamp of 1Dx (x=1 to 30) or 1Ex (x=1-15). My car was built the third week of May, 1971.

Alan

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