1966 alternator

[Dwane Mattmuller]

I'm trying to decode an alternator on a 1966 roadster that's CLEARLY stamped 1100750, 55A, 6D18. The "55A" is what doesn't make sense. Non of my books and manuals have it listed for any GM vehicle. I beginning to think it was misstamped???? Does anybody know if this could be an original alternator?

Dwane

[Peter L.]

Re: 1966 alternator

Dwane - Very interesting and just when we think we have seen it all. You're right that it's been mis-stamped because you wouldn't expect it to be stamped 55A if it's a 750. While all things are possible, I can't help being very curious because I have two cars w/ 1100750 alternators and both of those alternators are clearly stamped 61A. My '66 Chevelle alternator is close in date and it is stamped

1100750 61A
6D15 12vNEG

You can check the inside of the front frame for the production date of the casting and see if the production "clock" embossed on the frame shows a casting date before April 1966. The clocks I've seen have the last 2 digits of the year in a circle, i.e. 66 and 12 segments around the year designator circle. The production weeks are designated by a dot represnting the weeks of the month where 1 dot would indicate the first week of the month. The rear frame also has a similar clock.

Pete

[Joe L.]

Re: 1966 alternator

Dwane-----

I've seen this before. One case that immediately comes to mind is a GM #1100882 alternator that I have [not for sale]. The GM #1100882 is "officially" a 61 amp alternator. However, the one I have is stamped "55A". It carries a late 1968 date code, too, so it's very likely an original PRODUCTION alternator that once resided on a Corvette which "officially" had a 61 amp alternator. I've seen the same sort of thing with 37 and 42 amp alternators, too.

Why did this occur? I don't know, for sure. However, I can tell you this: there is absolutely no difference in the component make-up of a 55 amp and 61 amp alternator. Likewise, there is no difference between a 37 amp and a 42 amp. I strongly suspect that there is some "esoteric" rating system thing at work here. The fact that there are, apparently, known examples of the 1100750 alternator that are stamped both "55A" and "61A" and the 1100882 stamped "55A" and "61A" just about corroborates that theory. Certainly, there are no internal differences bewteen 2 alternators of the same GM part number.

I really don't think that this is a "mis-stamp" situation, either. If you had a 1100750 that was stamped "37A" or "42A", then I'd say that would be a mis-stamp, for sure. However, the fact that we're talking about an alternator generally considered (and specified by GM) as a 61 amp but stamped "55A" leads me to believe that it's not a mis-stamp situation for the reasons I described above.